[PATCH v3 00/10] riscv: Userspace pointer masking and tagged address ABI

[PATCH v3 00/10] riscv: Userspace pointer masking and tagged address ABI

[Samuel Holland]

RISC-V defines three extensions for pointer masking[1]:
 - Smmpm: configured in M-mode, affects M-mode
 - Smnpm: configured in M-mode, affects the next lower mode (S or U-mode)
 - Ssnpm: configured in S-mode, affects the next lower mode (VS, VU, or U-mode)

This series adds support for configuring Smnpm or Ssnpm (depending on
which privilege mode the kernel is running in) to allow pointer masking
in userspace (VU or U-mode), extending the PR_SET_TAGGED_ADDR_CTRL API
from arm64. Unlike arm64 TBI, userspace pointer masking is not enabled
by default on RISC-V. Additionally, the tag width (referred to as PMLEN)
is variable, so userspace needs to ask the kernel for a specific tag
width, which is interpreted as a lower bound on the number of tag bits.

This series also adds support for a tagged address ABI similar to arm64
and x86. Since accesses from the kernel to user memory use the kernel's
pointer masking configuration, not the user's, the kernel must untag
user pointers in software before dereferencing them. And since the tag
width is variable, as with LAM on x86, it must be kept the same across
all threads in a process so untagged_addr_remote() can work.

This series depends on my per-thread envcfg series[3].

This series can be tested in QEMU by applying a patch set[2].

KASAN support will be added in a separate patch series.

[1]: https://github.com/riscv/riscv-j-extension/releases/download/pointer-masking-v1.0.0-rc2/pointer-masking-v1.0.0-rc2.pdf
[2]: https://lore.kernel.org/qemu-devel/20240511101053.1875596-1-me@deliversmonkey.space/
[3]: https://lore.kernel.org/linux-riscv/20240814081126.956287-1-samuel.holland@sifive.com/

Changes in v3:
 - Note in the commit message that the ISA extension spec is frozen
 - Rebase on riscv/for-next (ISA extension list conflicts)
 - Remove RISCV_ISA_EXT_SxPM, which was not used anywhere
 - Use shifts instead of large numbers in ENVCFG_PMM* macro definitions
 - Rename CONFIG_RISCV_ISA_POINTER_MASKING to CONFIG_RISCV_ISA_SUPM,
   since it only controls the userspace part of pointer masking
 - Use IS_ENABLED instead of #ifdef when possible
 - Use an enum for the supported PMLEN values
 - Simplify the logic in set_tagged_addr_ctrl()
 - Use IS_ENABLED instead of #ifdef when possible
 - Implement mm_untag_mask()
 - Remove pmlen from struct thread_info (now only in mm_context_t)

Changes in v2:
 - Drop patch 4 ("riscv: Define is_compat_thread()"), as an equivalent
   patch was already applied
 - Move patch 5 ("riscv: Split per-CPU and per-thread envcfg bits") to a
   different series[3]
 - Update pointer masking specification version reference
 - Provide macros for the extension affecting the kernel and userspace
 - Use the correct name for the hstatus.HUPMM field
 - Rebase on riscv/linux.git for-next
 - Add and use the envcfg_update_bits() helper function
 - Inline flush_tagged_addr_state()
 - Implement untagged_addr_remote()
 - Restrict PMLEN changes once a process is multithreaded
 - Rename "tags" directory to "pm" to avoid .gitignore rules
 - Add .gitignore file to ignore the compiled selftest binary
 - Write to a pipe to force dereferencing the user pointer
 - Handle SIGSEGV in the child process to reduce dmesg noise
 - Export Supm via hwprobe
 - Export Smnpm and Ssnpm to KVM guests

Samuel Holland (10):
  dt-bindings: riscv: Add pointer masking ISA extensions
  riscv: Add ISA extension parsing for pointer masking
  riscv: Add CSR definitions for pointer masking
  riscv: Add support for userspace pointer masking
  riscv: Add support for the tagged address ABI
  riscv: Allow ptrace control of the tagged address ABI
  selftests: riscv: Add a pointer masking test
  riscv: hwprobe: Export the Supm ISA extension
  RISC-V: KVM: Allow Smnpm and Ssnpm extensions for guests
  KVM: riscv: selftests: Add Smnpm and Ssnpm to get-reg-list test

 Documentation/arch/riscv/hwprobe.rst          |   3 +
 .../devicetree/bindings/riscv/extensions.yaml |  18 +
 arch/riscv/Kconfig                            |  11 +
 arch/riscv/include/asm/csr.h                  |  16 +
 arch/riscv/include/asm/hwcap.h                |   5 +
 arch/riscv/include/asm/mmu.h                  |   7 +
 arch/riscv/include/asm/mmu_context.h          |  13 +
 arch/riscv/include/asm/processor.h            |   8 +
 arch/riscv/include/asm/switch_to.h            |  11 +
 arch/riscv/include/asm/uaccess.h              |  58 ++-
 arch/riscv/include/uapi/asm/hwprobe.h         |   1 +
 arch/riscv/include/uapi/asm/kvm.h             |   2 +
 arch/riscv/kernel/cpufeature.c                |   3 +
 arch/riscv/kernel/process.c                   | 153 ++++++++
 arch/riscv/kernel/ptrace.c                    |  42 +++
 arch/riscv/kernel/sys_hwprobe.c               |   3 +
 arch/riscv/kvm/vcpu_onereg.c                  |   3 +
 include/uapi/linux/elf.h                      |   1 +
 include/uapi/linux/prctl.h                    |   3 +
 .../selftests/kvm/riscv/get-reg-list.c        |   8 +
 tools/testing/selftests/riscv/Makefile        |   2 +-
 tools/testing/selftests/riscv/pm/.gitignore   |   1 +
 tools/testing/selftests/riscv/pm/Makefile     |  10 +
 .../selftests/riscv/pm/pointer_masking.c      | 330 ++++++++++++++++++
 24 files changed, 706 insertions(+), 6 deletions(-)
 create mode 100644 tools/testing/selftests/riscv/pm/.gitignore
 create mode 100644 tools/testing/selftests/riscv/pm/Makefile
 create mode 100644 tools/testing/selftests/riscv/pm/pointer_masking.c

-- 
2.45.1

[PATCH v3 01/10] dt-bindings: riscv: Add pointer masking ISA extensions

[Samuel Holland]

The RISC-V Pointer Masking specification defines three extensions:
Smmpm, Smnpm, and Ssnpm. Document the behavior of these extensions as
following the current draft of the specification, which is frozen at
version 1.0.0-rc2.

Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
---

Changes in v3:
 - Note in the commit message that the ISA extension spec is frozen

Changes in v2:
 - Update pointer masking specification version reference

 .../devicetree/bindings/riscv/extensions.yaml  | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/Documentation/devicetree/bindings/riscv/extensions.yaml b/Documentation/devicetree/bindings/riscv/extensions.yaml
index a06dbc6b4928..a6d685791221 100644
--- a/Documentation/devicetree/bindings/riscv/extensions.yaml
+++ b/Documentation/devicetree/bindings/riscv/extensions.yaml
@@ -128,6 +128,18 @@ properties:
             changes to interrupts as frozen at commit ccbddab ("Merge pull
             request #42 from riscv/jhauser-2023-RC4") of riscv-aia.
 
+        - const: smmpm
+          description: |
+            The standard Smmpm extension for M-mode pointer masking as defined
+            at commit 654a5c4a7725 ("Update PDF and version number.") of
+            riscv-j-extension.
+
+        - const: smnpm
+          description: |
+            The standard Smnpm extension for next-mode pointer masking as defined
+            at commit 654a5c4a7725 ("Update PDF and version number.") of
+            riscv-j-extension.
+
         - const: smstateen
           description: |
             The standard Smstateen extension for controlling access to CSRs
@@ -147,6 +159,12 @@ properties:
             and mode-based filtering as ratified at commit 01d1df0 ("Add ability
             to manually trigger workflow. (#2)") of riscv-count-overflow.
 
+        - const: ssnpm
+          description: |
+            The standard Ssnpm extension for next-mode pointer masking as defined
+            at commit 654a5c4a7725 ("Update PDF and version number.") of
+            riscv-j-extension.
+
         - const: sstc
           description: |
             The standard Sstc supervisor-level extension for time compare as
-- 
2.45.1

[PATCH v3 02/10] riscv: Add ISA extension parsing for pointer masking

[Samuel Holland]

The RISC-V Pointer Masking specification defines three extensions:
Smmpm, Smnpm, and Ssnpm. Add support for parsing each of them. The
specific extension which provides pointer masking support to userspace
(Supm) depends on the kernel's privilege mode, so provide a macro to
abstract this selection.

Smmpm implies the existence of the mseccfg CSR. As it is the only user
of this CSR so far, there is no need for an Xlinuxmseccfg extension.

Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
---

Changes in v3:
 - Rebase on riscv/for-next (ISA extension list conflicts)
 - Remove RISCV_ISA_EXT_SxPM, which was not used anywhere

Changes in v2:
 - Provide macros for the extension affecting the kernel and userspace

 arch/riscv/include/asm/hwcap.h | 5 +++++
 arch/riscv/kernel/cpufeature.c | 3 +++
 2 files changed, 8 insertions(+)

diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
index 5a0bd27fd11a..aff21c6fc9b6 100644
--- a/arch/riscv/include/asm/hwcap.h
+++ b/arch/riscv/include/asm/hwcap.h
@@ -92,6 +92,9 @@
 #define RISCV_ISA_EXT_ZCF		83
 #define RISCV_ISA_EXT_ZCMOP		84
 #define RISCV_ISA_EXT_ZAWRS		85
+#define RISCV_ISA_EXT_SMMPM		86
+#define RISCV_ISA_EXT_SMNPM		87
+#define RISCV_ISA_EXT_SSNPM		88
 
 #define RISCV_ISA_EXT_XLINUXENVCFG	127
 
@@ -100,8 +103,10 @@
 
 #ifdef CONFIG_RISCV_M_MODE
 #define RISCV_ISA_EXT_SxAIA		RISCV_ISA_EXT_SMAIA
+#define RISCV_ISA_EXT_SUPM		RISCV_ISA_EXT_SMNPM
 #else
 #define RISCV_ISA_EXT_SxAIA		RISCV_ISA_EXT_SSAIA
+#define RISCV_ISA_EXT_SUPM		RISCV_ISA_EXT_SSNPM
 #endif
 
 #endif /* _ASM_RISCV_HWCAP_H */
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index b3b9735cb19a..ba3dc16e14dc 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -377,9 +377,12 @@ const struct riscv_isa_ext_data riscv_isa_ext[] = {
 	__RISCV_ISA_EXT_BUNDLE(zvksg, riscv_zvksg_bundled_exts),
 	__RISCV_ISA_EXT_DATA(zvkt, RISCV_ISA_EXT_ZVKT),
 	__RISCV_ISA_EXT_DATA(smaia, RISCV_ISA_EXT_SMAIA),
+	__RISCV_ISA_EXT_DATA(smmpm, RISCV_ISA_EXT_SMMPM),
+	__RISCV_ISA_EXT_SUPERSET(smnpm, RISCV_ISA_EXT_SMNPM, riscv_xlinuxenvcfg_exts),
 	__RISCV_ISA_EXT_DATA(smstateen, RISCV_ISA_EXT_SMSTATEEN),
 	__RISCV_ISA_EXT_DATA(ssaia, RISCV_ISA_EXT_SSAIA),
 	__RISCV_ISA_EXT_DATA(sscofpmf, RISCV_ISA_EXT_SSCOFPMF),
+	__RISCV_ISA_EXT_SUPERSET(ssnpm, RISCV_ISA_EXT_SSNPM, riscv_xlinuxenvcfg_exts),
 	__RISCV_ISA_EXT_DATA(sstc, RISCV_ISA_EXT_SSTC),
 	__RISCV_ISA_EXT_DATA(svinval, RISCV_ISA_EXT_SVINVAL),
 	__RISCV_ISA_EXT_DATA(svnapot, RISCV_ISA_EXT_SVNAPOT),
-- 
2.45.1

[PATCH v3 03/10] riscv: Add CSR definitions for pointer masking

[Samuel Holland]

Pointer masking is controlled via a two-bit PMM field, which appears in
various CSRs depending on which extensions are implemented. Smmpm adds
the field to mseccfg; Smnpm adds the field to menvcfg; Ssnpm adds the
field to senvcfg. If the H extension is implemented, Ssnpm also defines
henvcfg.PMM and hstatus.HUPMM.

Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
---

Changes in v3:
 - Use shifts instead of large numbers in ENVCFG_PMM* macro definitions

Changes in v2:
 - Use the correct name for the hstatus.HUPMM field

 arch/riscv/include/asm/csr.h | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/arch/riscv/include/asm/csr.h b/arch/riscv/include/asm/csr.h
index 25966995da04..fe5d4eb9adea 100644
--- a/arch/riscv/include/asm/csr.h
+++ b/arch/riscv/include/asm/csr.h
@@ -119,6 +119,10 @@
 
 /* HSTATUS flags */
 #ifdef CONFIG_64BIT
+#define HSTATUS_HUPMM		_AC(0x3000000000000, UL)
+#define HSTATUS_HUPMM_PMLEN_0	_AC(0x0000000000000, UL)
+#define HSTATUS_HUPMM_PMLEN_7	_AC(0x2000000000000, UL)
+#define HSTATUS_HUPMM_PMLEN_16	_AC(0x3000000000000, UL)
 #define HSTATUS_VSXL		_AC(0x300000000, UL)
 #define HSTATUS_VSXL_SHIFT	32
 #endif
@@ -195,6 +199,10 @@
 /* xENVCFG flags */
 #define ENVCFG_STCE			(_AC(1, ULL) << 63)
 #define ENVCFG_PBMTE			(_AC(1, ULL) << 62)
+#define ENVCFG_PMM			(_AC(0x3, ULL) << 32)
+#define ENVCFG_PMM_PMLEN_0		(_AC(0x0, ULL) << 32)
+#define ENVCFG_PMM_PMLEN_7		(_AC(0x2, ULL) << 32)
+#define ENVCFG_PMM_PMLEN_16		(_AC(0x3, ULL) << 32)
 #define ENVCFG_CBZE			(_AC(1, UL) << 7)
 #define ENVCFG_CBCFE			(_AC(1, UL) << 6)
 #define ENVCFG_CBIE_SHIFT		4
@@ -216,6 +224,12 @@
 #define SMSTATEEN0_SSTATEEN0_SHIFT	63
 #define SMSTATEEN0_SSTATEEN0		(_ULL(1) << SMSTATEEN0_SSTATEEN0_SHIFT)
 
+/* mseccfg bits */
+#define MSECCFG_PMM			ENVCFG_PMM
+#define MSECCFG_PMM_PMLEN_0		ENVCFG_PMM_PMLEN_0
+#define MSECCFG_PMM_PMLEN_7		ENVCFG_PMM_PMLEN_7
+#define MSECCFG_PMM_PMLEN_16		ENVCFG_PMM_PMLEN_16
+
 /* symbolic CSR names: */
 #define CSR_CYCLE		0xc00
 #define CSR_TIME		0xc01
@@ -382,6 +396,8 @@
 #define CSR_MIP			0x344
 #define CSR_PMPCFG0		0x3a0
 #define CSR_PMPADDR0		0x3b0
+#define CSR_MSECCFG		0x747
+#define CSR_MSECCFGH		0x757
 #define CSR_MVENDORID		0xf11
 #define CSR_MARCHID		0xf12
 #define CSR_MIMPID		0xf13
-- 
2.45.1

[PATCH v3 04/10] riscv: Add support for userspace pointer masking

[Samuel Holland]

RISC-V supports pointer masking with a variable number of tag bits
(which is called "PMLEN" in the specification) and which is configured
at the next higher privilege level.

Wire up the PR_SET_TAGGED_ADDR_CTRL and PR_GET_TAGGED_ADDR_CTRL prctls
so userspace can request a lower bound on the number of tag bits and
determine the actual number of tag bits. As with arm64's
PR_TAGGED_ADDR_ENABLE, the pointer masking configuration is
thread-scoped, inherited on clone() and fork() and cleared on execve().

Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
---

Changes in v3:
 - Rename CONFIG_RISCV_ISA_POINTER_MASKING to CONFIG_RISCV_ISA_SUPM,
   since it only controls the userspace part of pointer masking
 - Use IS_ENABLED instead of #ifdef when possible
 - Use an enum for the supported PMLEN values
 - Simplify the logic in set_tagged_addr_ctrl()

Changes in v2:
 - Rebase on riscv/linux.git for-next
 - Add and use the envcfg_update_bits() helper function
 - Inline flush_tagged_addr_state()

 arch/riscv/Kconfig                 | 11 ++++
 arch/riscv/include/asm/processor.h |  8 +++
 arch/riscv/include/asm/switch_to.h | 11 ++++
 arch/riscv/kernel/process.c        | 90 ++++++++++++++++++++++++++++++
 include/uapi/linux/prctl.h         |  3 +
 5 files changed, 123 insertions(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 0f3cd7c3a436..817437157138 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -512,6 +512,17 @@ config RISCV_ISA_C
 
 	  If you don't know what to do here, say Y.
 
+config RISCV_ISA_SUPM
+	bool "Supm extension for userspace pointer masking"
+	depends on 64BIT
+	default y
+	help
+	  Add support for pointer masking in userspace (Supm) when the
+	  underlying hardware extension (Smnpm or Ssnpm) is detected at boot.
+
+	  If this option is disabled, userspace will be unable to use
+	  the prctl(PR_{SET,GET}_TAGGED_ADDR_CTRL) API.
+
 config RISCV_ISA_SVNAPOT
 	bool "Svnapot extension support for supervisor mode NAPOT pages"
 	depends on 64BIT && MMU
diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
index 586e4ab701c4..5c4d4fb97314 100644
--- a/arch/riscv/include/asm/processor.h
+++ b/arch/riscv/include/asm/processor.h
@@ -200,6 +200,14 @@ extern int set_unalign_ctl(struct task_struct *tsk, unsigned int val);
 #define RISCV_SET_ICACHE_FLUSH_CTX(arg1, arg2)	riscv_set_icache_flush_ctx(arg1, arg2)
 extern int riscv_set_icache_flush_ctx(unsigned long ctx, unsigned long per_thread);
 
+#ifdef CONFIG_RISCV_ISA_SUPM
+/* PR_{SET,GET}_TAGGED_ADDR_CTRL prctl */
+long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg);
+long get_tagged_addr_ctrl(struct task_struct *task);
+#define SET_TAGGED_ADDR_CTRL(arg)	set_tagged_addr_ctrl(current, arg)
+#define GET_TAGGED_ADDR_CTRL()		get_tagged_addr_ctrl(current)
+#endif
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* _ASM_RISCV_PROCESSOR_H */
diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/switch_to.h
index 9685cd85e57c..94e33216b2d9 100644
--- a/arch/riscv/include/asm/switch_to.h
+++ b/arch/riscv/include/asm/switch_to.h
@@ -70,6 +70,17 @@ static __always_inline bool has_fpu(void) { return false; }
 #define __switch_to_fpu(__prev, __next) do { } while (0)
 #endif
 
+static inline void envcfg_update_bits(struct task_struct *task,
+				      unsigned long mask, unsigned long val)
+{
+	unsigned long envcfg;
+
+	envcfg = (task->thread.envcfg & ~mask) | val;
+	task->thread.envcfg = envcfg;
+	if (task == current)
+		csr_write(CSR_ENVCFG, envcfg);
+}
+
 static inline void __switch_to_envcfg(struct task_struct *next)
 {
 	asm volatile (ALTERNATIVE("nop", "csrw " __stringify(CSR_ENVCFG) ", %0",
diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
index e4bc61c4e58a..1280a7c4a412 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -7,6 +7,7 @@
  * Copyright (C) 2017 SiFive
  */
 
+#include <linux/bitfield.h>
 #include <linux/cpu.h>
 #include <linux/kernel.h>
 #include <linux/sched.h>
@@ -171,6 +172,9 @@ void flush_thread(void)
 	memset(&current->thread.vstate, 0, sizeof(struct __riscv_v_ext_state));
 	clear_tsk_thread_flag(current, TIF_RISCV_V_DEFER_RESTORE);
 #endif
+	if (IS_ENABLED(CONFIG_RISCV_ISA_SUPM) &&
+	    riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM))
+		envcfg_update_bits(current, ENVCFG_PMM, ENVCFG_PMM_PMLEN_0);
 }
 
 void arch_release_task_struct(struct task_struct *tsk)
@@ -233,3 +237,89 @@ void __init arch_task_cache_init(void)
 {
 	riscv_v_setup_ctx_cache();
 }
+
+#ifdef CONFIG_RISCV_ISA_SUPM
+enum {
+	PMLEN_0 = 0,
+	PMLEN_7 = 7,
+	PMLEN_16 = 16,
+};
+
+static bool have_user_pmlen_7;
+static bool have_user_pmlen_16;
+
+long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg)
+{
+	unsigned long valid_mask = PR_PMLEN_MASK;
+	struct thread_info *ti = task_thread_info(task);
+	unsigned long pmm;
+	u8 pmlen;
+
+	if (is_compat_thread(ti))
+		return -EINVAL;
+
+	if (arg & ~valid_mask)
+		return -EINVAL;
+
+	/*
+	 * Prefer the smallest PMLEN that satisfies the user's request,
+	 * in case choosing a larger PMLEN has a performance impact.
+	 */
+	pmlen = FIELD_GET(PR_PMLEN_MASK, arg);
+	if (pmlen == PMLEN_0)
+		pmm = ENVCFG_PMM_PMLEN_0;
+	else if (pmlen <= PMLEN_7 && have_user_pmlen_7)
+		pmm = ENVCFG_PMM_PMLEN_7;
+	else if (pmlen <= PMLEN_16 && have_user_pmlen_16)
+		pmm = ENVCFG_PMM_PMLEN_16;
+	else
+		return -EINVAL;
+
+	envcfg_update_bits(task, ENVCFG_PMM, pmm);
+
+	return 0;
+}
+
+long get_tagged_addr_ctrl(struct task_struct *task)
+{
+	struct thread_info *ti = task_thread_info(task);
+	long ret = 0;
+
+	if (is_compat_thread(ti))
+		return -EINVAL;
+
+	switch (task->thread.envcfg & ENVCFG_PMM) {
+	case ENVCFG_PMM_PMLEN_7:
+		ret = FIELD_PREP(PR_PMLEN_MASK, PMLEN_7);
+		break;
+	case ENVCFG_PMM_PMLEN_16:
+		ret = FIELD_PREP(PR_PMLEN_MASK, PMLEN_16);
+		break;
+	}
+
+	return ret;
+}
+
+static bool try_to_set_pmm(unsigned long value)
+{
+	csr_set(CSR_ENVCFG, value);
+	return (csr_read_clear(CSR_ENVCFG, ENVCFG_PMM) & ENVCFG_PMM) == value;
+}
+
+static int __init tagged_addr_init(void)
+{
+	if (!riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM))
+		return 0;
+
+	/*
+	 * envcfg.PMM is a WARL field. Detect which values are supported.
+	 * Assume the supported PMLEN values are the same on all harts.
+	 */
+	csr_clear(CSR_ENVCFG, ENVCFG_PMM);
+	have_user_pmlen_7 = try_to_set_pmm(ENVCFG_PMM_PMLEN_7);
+	have_user_pmlen_16 = try_to_set_pmm(ENVCFG_PMM_PMLEN_16);
+
+	return 0;
+}
+core_initcall(tagged_addr_init);
+#endif	/* CONFIG_RISCV_ISA_SUPM */
diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index 35791791a879..6e84c827869b 100644
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -244,6 +244,9 @@ struct prctl_mm_map {
 # define PR_MTE_TAG_MASK		(0xffffUL << PR_MTE_TAG_SHIFT)
 /* Unused; kept only for source compatibility */
 # define PR_MTE_TCF_SHIFT		1
+/* RISC-V pointer masking tag length */
+# define PR_PMLEN_SHIFT			24
+# define PR_PMLEN_MASK			(0x7fUL << PR_PMLEN_SHIFT)
 
 /* Control reclaim behavior when allocating memory */
 #define PR_SET_IO_FLUSHER		57
-- 
2.45.1

[PATCH v3 05/10] riscv: Add support for the tagged address ABI

[Samuel Holland]

When pointer masking is enabled for userspace, the kernel can accept
tagged pointers as arguments to some system calls. Allow this by
untagging the pointers in access_ok() and the uaccess routines. The
uaccess routines must peform untagging in software because U-mode and
S-mode have entirely separate pointer masking configurations. In fact,
hardware may not even implement pointer masking for S-mode.

Since the number of tag bits is variable, untagged_addr_remote() needs
to know what PMLEN to use for the remote mm. Therefore, the pointer
masking mode must be the same for all threads sharing an mm. Enforce
this with a lock flag in the mm context, as x86 does for LAM. The flag
gets reset in init_new_context() during fork(), as the new mm is no
longer multithreaded.

Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
---

Changes in v3:
 - Use IS_ENABLED instead of #ifdef when possible
 - Implement mm_untag_mask()
 - Remove pmlen from struct thread_info (now only in mm_context_t)

Changes in v2:
 - Implement untagged_addr_remote()
 - Restrict PMLEN changes once a process is multithreaded

 arch/riscv/include/asm/mmu.h         |  7 +++
 arch/riscv/include/asm/mmu_context.h | 13 +++++
 arch/riscv/include/asm/uaccess.h     | 58 ++++++++++++++++++++--
 arch/riscv/kernel/process.c          | 73 ++++++++++++++++++++++++++--
 4 files changed, 141 insertions(+), 10 deletions(-)

diff --git a/arch/riscv/include/asm/mmu.h b/arch/riscv/include/asm/mmu.h
index c9e03e9da3dc..1cc90465d75b 100644
--- a/arch/riscv/include/asm/mmu.h
+++ b/arch/riscv/include/asm/mmu.h
@@ -25,9 +25,16 @@ typedef struct {
 #ifdef CONFIG_BINFMT_ELF_FDPIC
 	unsigned long exec_fdpic_loadmap;
 	unsigned long interp_fdpic_loadmap;
+#endif
+	unsigned long flags;
+#ifdef CONFIG_RISCV_ISA_SUPM
+	u8 pmlen;
 #endif
 } mm_context_t;
 
+/* Lock the pointer masking mode because this mm is multithreaded */
+#define MM_CONTEXT_LOCK_PMLEN	0
+
 #define cntx2asid(cntx)		((cntx) & SATP_ASID_MASK)
 #define cntx2version(cntx)	((cntx) & ~SATP_ASID_MASK)
 
diff --git a/arch/riscv/include/asm/mmu_context.h b/arch/riscv/include/asm/mmu_context.h
index 7030837adc1a..8c4bc49a3a0f 100644
--- a/arch/riscv/include/asm/mmu_context.h
+++ b/arch/riscv/include/asm/mmu_context.h
@@ -20,6 +20,9 @@ void switch_mm(struct mm_struct *prev, struct mm_struct *next,
 static inline void activate_mm(struct mm_struct *prev,
 			       struct mm_struct *next)
 {
+#ifdef CONFIG_RISCV_ISA_SUPM
+	next->context.pmlen = 0;
+#endif
 	switch_mm(prev, next, NULL);
 }
 
@@ -30,11 +33,21 @@ static inline int init_new_context(struct task_struct *tsk,
 #ifdef CONFIG_MMU
 	atomic_long_set(&mm->context.id, 0);
 #endif
+	if (IS_ENABLED(CONFIG_RISCV_ISA_SUPM))
+		clear_bit(MM_CONTEXT_LOCK_PMLEN, &mm->context.flags);
 	return 0;
 }
 
 DECLARE_STATIC_KEY_FALSE(use_asid_allocator);
 
+#ifdef CONFIG_RISCV_ISA_SUPM
+#define mm_untag_mask mm_untag_mask
+static inline unsigned long mm_untag_mask(struct mm_struct *mm)
+{
+	return -1UL >> mm->context.pmlen;
+}
+#endif
+
 #include <asm-generic/mmu_context.h>
 
 #endif /* _ASM_RISCV_MMU_CONTEXT_H */
diff --git a/arch/riscv/include/asm/uaccess.h b/arch/riscv/include/asm/uaccess.h
index 72ec1d9bd3f3..6416559232a2 100644
--- a/arch/riscv/include/asm/uaccess.h
+++ b/arch/riscv/include/asm/uaccess.h
@@ -9,8 +9,56 @@
 #define _ASM_RISCV_UACCESS_H
 
 #include <asm/asm-extable.h>
+#include <asm/cpufeature.h>
 #include <asm/pgtable.h>		/* for TASK_SIZE */
 
+#ifdef CONFIG_RISCV_ISA_SUPM
+static inline unsigned long __untagged_addr(unsigned long addr)
+{
+	if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM)) {
+		u8 pmlen = current->mm->context.pmlen;
+
+		/* Virtual addresses are sign-extended; physical addresses are zero-extended. */
+		if (IS_ENABLED(CONFIG_MMU))
+			return (long)(addr << pmlen) >> pmlen;
+		else
+			return (addr << pmlen) >> pmlen;
+	}
+
+	return addr;
+}
+
+#define untagged_addr(addr) ({						\
+	unsigned long __addr = (__force unsigned long)(addr);		\
+	(__force __typeof__(addr))__untagged_addr(__addr);		\
+})
+
+static inline unsigned long __untagged_addr_remote(struct mm_struct *mm, unsigned long addr)
+{
+	if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM)) {
+		u8 pmlen = mm->context.pmlen;
+
+		/* Virtual addresses are sign-extended; physical addresses are zero-extended. */
+		if (IS_ENABLED(CONFIG_MMU))
+			return (long)(addr << pmlen) >> pmlen;
+		else
+			return (addr << pmlen) >> pmlen;
+	}
+
+	return addr;
+}
+
+#define untagged_addr_remote(mm, addr) ({				\
+	unsigned long __addr = (__force unsigned long)(addr);		\
+	mmap_assert_locked(mm);						\
+	(__force __typeof__(addr))__untagged_addr_remote(mm, __addr);	\
+})
+
+#define access_ok(addr, size) likely(__access_ok(untagged_addr(addr), size))
+#else
+#define untagged_addr(addr) (addr)
+#endif
+
 /*
  * User space memory access functions
  */
@@ -130,7 +178,7 @@ do {								\
  */
 #define __get_user(x, ptr)					\
 ({								\
-	const __typeof__(*(ptr)) __user *__gu_ptr = (ptr);	\
+	const __typeof__(*(ptr)) __user *__gu_ptr = untagged_addr(ptr); \
 	long __gu_err = 0;					\
 								\
 	__chk_user_ptr(__gu_ptr);				\
@@ -246,7 +294,7 @@ do {								\
  */
 #define __put_user(x, ptr)					\
 ({								\
-	__typeof__(*(ptr)) __user *__gu_ptr = (ptr);		\
+	__typeof__(*(ptr)) __user *__gu_ptr = untagged_addr(ptr); \
 	__typeof__(*__gu_ptr) __val = (x);			\
 	long __pu_err = 0;					\
 								\
@@ -293,13 +341,13 @@ unsigned long __must_check __asm_copy_from_user(void *to,
 static inline unsigned long
 raw_copy_from_user(void *to, const void __user *from, unsigned long n)
 {
-	return __asm_copy_from_user(to, from, n);
+	return __asm_copy_from_user(to, untagged_addr(from), n);
 }
 
 static inline unsigned long
 raw_copy_to_user(void __user *to, const void *from, unsigned long n)
 {
-	return __asm_copy_to_user(to, from, n);
+	return __asm_copy_to_user(untagged_addr(to), from, n);
 }
 
 extern long strncpy_from_user(char *dest, const char __user *src, long count);
@@ -314,7 +362,7 @@ unsigned long __must_check clear_user(void __user *to, unsigned long n)
 {
 	might_fault();
 	return access_ok(to, n) ?
-		__clear_user(to, n) : n;
+		__clear_user(untagged_addr(to), n) : n;
 }
 
 #define __get_kernel_nofault(dst, src, type, err_label)			\
diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
index 1280a7c4a412..f4d8e5c3bb84 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -203,6 +203,10 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 	unsigned long tls = args->tls;
 	struct pt_regs *childregs = task_pt_regs(p);
 
+	/* Ensure all threads in this mm have the same pointer masking mode. */
+	if (IS_ENABLED(CONFIG_RISCV_ISA_SUPM) && p->mm && (clone_flags & CLONE_VM))
+		set_bit(MM_CONTEXT_LOCK_PMLEN, &p->mm->context.flags);
+
 	memset(&p->thread.s, 0, sizeof(p->thread.s));
 
 	/* p->thread holds context to be restored by __switch_to() */
@@ -248,10 +252,16 @@ enum {
 static bool have_user_pmlen_7;
 static bool have_user_pmlen_16;
 
+/*
+ * Control the relaxed ABI allowing tagged user addresses into the kernel.
+ */
+static unsigned int tagged_addr_disabled;
+
 long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg)
 {
-	unsigned long valid_mask = PR_PMLEN_MASK;
+	unsigned long valid_mask = PR_PMLEN_MASK | PR_TAGGED_ADDR_ENABLE;
 	struct thread_info *ti = task_thread_info(task);
+	struct mm_struct *mm = task->mm;
 	unsigned long pmm;
 	u8 pmlen;
 
@@ -266,16 +276,41 @@ long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg)
 	 * in case choosing a larger PMLEN has a performance impact.
 	 */
 	pmlen = FIELD_GET(PR_PMLEN_MASK, arg);
-	if (pmlen == PMLEN_0)
+	if (pmlen == PMLEN_0) {
 		pmm = ENVCFG_PMM_PMLEN_0;
-	else if (pmlen <= PMLEN_7 && have_user_pmlen_7)
+	} else if (pmlen <= PMLEN_7 && have_user_pmlen_7) {
+		pmlen = PMLEN_7;
 		pmm = ENVCFG_PMM_PMLEN_7;
-	else if (pmlen <= PMLEN_16 && have_user_pmlen_16)
+	} else if (pmlen <= PMLEN_16 && have_user_pmlen_16) {
+		pmlen = PMLEN_16;
 		pmm = ENVCFG_PMM_PMLEN_16;
-	else
+	} else {
 		return -EINVAL;
+	}
+
+	/*
+	 * Do not allow the enabling of the tagged address ABI if globally
+	 * disabled via sysctl abi.tagged_addr_disabled, if pointer masking
+	 * is disabled for userspace.
+	 */
+	if (arg & PR_TAGGED_ADDR_ENABLE && (tagged_addr_disabled || !pmlen))
+		return -EINVAL;
+
+	if (!(arg & PR_TAGGED_ADDR_ENABLE))
+		pmlen = PMLEN_0;
+
+	if (mmap_write_lock_killable(mm))
+		return -EINTR;
+
+	if (test_bit(MM_CONTEXT_LOCK_PMLEN, &mm->context.flags) && mm->context.pmlen != pmlen) {
+		mmap_write_unlock(mm);
+		return -EBUSY;
+	}
 
 	envcfg_update_bits(task, ENVCFG_PMM, pmm);
+	mm->context.pmlen = pmlen;
+
+	mmap_write_unlock(mm);
 
 	return 0;
 }
@@ -288,6 +323,10 @@ long get_tagged_addr_ctrl(struct task_struct *task)
 	if (is_compat_thread(ti))
 		return -EINVAL;
 
+	/*
+	 * The mm context's pmlen is set only when the tagged address ABI is
+	 * enabled, so the effective PMLEN must be extracted from envcfg.PMM.
+	 */
 	switch (task->thread.envcfg & ENVCFG_PMM) {
 	case ENVCFG_PMM_PMLEN_7:
 		ret = FIELD_PREP(PR_PMLEN_MASK, PMLEN_7);
@@ -297,6 +336,9 @@ long get_tagged_addr_ctrl(struct task_struct *task)
 		break;
 	}
 
+	if (task->mm->context.pmlen)
+		ret |= PR_TAGGED_ADDR_ENABLE;
+
 	return ret;
 }
 
@@ -306,6 +348,24 @@ static bool try_to_set_pmm(unsigned long value)
 	return (csr_read_clear(CSR_ENVCFG, ENVCFG_PMM) & ENVCFG_PMM) == value;
 }
 
+/*
+ * Global sysctl to disable the tagged user addresses support. This control
+ * only prevents the tagged address ABI enabling via prctl() and does not
+ * disable it for tasks that already opted in to the relaxed ABI.
+ */
+
+static struct ctl_table tagged_addr_sysctl_table[] = {
+	{
+		.procname	= "tagged_addr_disabled",
+		.mode		= 0644,
+		.data		= &tagged_addr_disabled,
+		.maxlen		= sizeof(int),
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= SYSCTL_ONE,
+	},
+};
+
 static int __init tagged_addr_init(void)
 {
 	if (!riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM))
@@ -319,6 +379,9 @@ static int __init tagged_addr_init(void)
 	have_user_pmlen_7 = try_to_set_pmm(ENVCFG_PMM_PMLEN_7);
 	have_user_pmlen_16 = try_to_set_pmm(ENVCFG_PMM_PMLEN_16);
 
+	if (!register_sysctl("abi", tagged_addr_sysctl_table))
+		return -EINVAL;
+
 	return 0;
 }
 core_initcall(tagged_addr_init);
-- 
2.45.1

[PATCH v3 06/10] riscv: Allow ptrace control of the tagged address ABI

[Samuel Holland]

This allows a tracer to control the ABI of the tracee, as on arm64.

Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
---

(no changes since v1)

 arch/riscv/kernel/ptrace.c | 42 ++++++++++++++++++++++++++++++++++++++
 include/uapi/linux/elf.h   |  1 +
 2 files changed, 43 insertions(+)

diff --git a/arch/riscv/kernel/ptrace.c b/arch/riscv/kernel/ptrace.c
index 92731ff8c79a..ea67e9fb7a58 100644
--- a/arch/riscv/kernel/ptrace.c
+++ b/arch/riscv/kernel/ptrace.c
@@ -28,6 +28,9 @@ enum riscv_regset {
 #ifdef CONFIG_RISCV_ISA_V
 	REGSET_V,
 #endif
+#ifdef CONFIG_RISCV_ISA_SUPM
+	REGSET_TAGGED_ADDR_CTRL,
+#endif
 };
 
 static int riscv_gpr_get(struct task_struct *target,
@@ -152,6 +155,35 @@ static int riscv_vr_set(struct task_struct *target,
 }
 #endif
 
+#ifdef CONFIG_RISCV_ISA_SUPM
+static int tagged_addr_ctrl_get(struct task_struct *target,
+				const struct user_regset *regset,
+				struct membuf to)
+{
+	long ctrl = get_tagged_addr_ctrl(target);
+
+	if (IS_ERR_VALUE(ctrl))
+		return ctrl;
+
+	return membuf_write(&to, &ctrl, sizeof(ctrl));
+}
+
+static int tagged_addr_ctrl_set(struct task_struct *target,
+				const struct user_regset *regset,
+				unsigned int pos, unsigned int count,
+				const void *kbuf, const void __user *ubuf)
+{
+	int ret;
+	long ctrl;
+
+	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &ctrl, 0, -1);
+	if (ret)
+		return ret;
+
+	return set_tagged_addr_ctrl(target, ctrl);
+}
+#endif
+
 static const struct user_regset riscv_user_regset[] = {
 	[REGSET_X] = {
 		.core_note_type = NT_PRSTATUS,
@@ -182,6 +214,16 @@ static const struct user_regset riscv_user_regset[] = {
 		.set = riscv_vr_set,
 	},
 #endif
+#ifdef CONFIG_RISCV_ISA_SUPM
+	[REGSET_TAGGED_ADDR_CTRL] = {
+		.core_note_type = NT_RISCV_TAGGED_ADDR_CTRL,
+		.n = 1,
+		.size = sizeof(long),
+		.align = sizeof(long),
+		.regset_get = tagged_addr_ctrl_get,
+		.set = tagged_addr_ctrl_set,
+	},
+#endif
 };
 
 static const struct user_regset_view riscv_user_native_view = {
diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
index b54b313bcf07..9a32532d7264 100644
--- a/include/uapi/linux/elf.h
+++ b/include/uapi/linux/elf.h
@@ -448,6 +448,7 @@ typedef struct elf64_shdr {
 #define NT_MIPS_MSA	0x802		/* MIPS SIMD registers */
 #define NT_RISCV_CSR	0x900		/* RISC-V Control and Status Registers */
 #define NT_RISCV_VECTOR	0x901		/* RISC-V vector registers */
+#define NT_RISCV_TAGGED_ADDR_CTRL 0x902	/* RISC-V tagged address control (prctl()) */
 #define NT_LOONGARCH_CPUCFG	0xa00	/* LoongArch CPU config registers */
 #define NT_LOONGARCH_CSR	0xa01	/* LoongArch control and status registers */
 #define NT_LOONGARCH_LSX	0xa02	/* LoongArch Loongson SIMD Extension registers */
-- 
2.45.1

[PATCH v3 07/10] selftests: riscv: Add a pointer masking test

[Samuel Holland]

This test covers the behavior of the PR_SET_TAGGED_ADDR_CTRL and
PR_GET_TAGGED_ADDR_CTRL prctl() operations, their effects on the
userspace ABI, and their effects on the system call ABI.

Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
---

(no changes since v2)

Changes in v2:
 - Rename "tags" directory to "pm" to avoid .gitignore rules
 - Add .gitignore file to ignore the compiled selftest binary
 - Write to a pipe to force dereferencing the user pointer
 - Handle SIGSEGV in the child process to reduce dmesg noise

 tools/testing/selftests/riscv/Makefile        |   2 +-
 tools/testing/selftests/riscv/pm/.gitignore   |   1 +
 tools/testing/selftests/riscv/pm/Makefile     |  10 +
 .../selftests/riscv/pm/pointer_masking.c      | 330 ++++++++++++++++++
 4 files changed, 342 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/riscv/pm/.gitignore
 create mode 100644 tools/testing/selftests/riscv/pm/Makefile
 create mode 100644 tools/testing/selftests/riscv/pm/pointer_masking.c

diff --git a/tools/testing/selftests/riscv/Makefile b/tools/testing/selftests/riscv/Makefile
index 7ce03d832b64..2ee1d1548c5f 100644
--- a/tools/testing/selftests/riscv/Makefile
+++ b/tools/testing/selftests/riscv/Makefile
@@ -5,7 +5,7 @@
 ARCH ?= $(shell uname -m 2>/dev/null || echo not)
 
 ifneq (,$(filter $(ARCH),riscv))
-RISCV_SUBTARGETS ?= hwprobe vector mm sigreturn
+RISCV_SUBTARGETS ?= hwprobe mm pm sigreturn vector
 else
 RISCV_SUBTARGETS :=
 endif
diff --git a/tools/testing/selftests/riscv/pm/.gitignore b/tools/testing/selftests/riscv/pm/.gitignore
new file mode 100644
index 000000000000..b38358f91c4d
--- /dev/null
+++ b/tools/testing/selftests/riscv/pm/.gitignore
@@ -0,0 +1 @@
+pointer_masking
diff --git a/tools/testing/selftests/riscv/pm/Makefile b/tools/testing/selftests/riscv/pm/Makefile
new file mode 100644
index 000000000000..ed82ff9c664e
--- /dev/null
+++ b/tools/testing/selftests/riscv/pm/Makefile
@@ -0,0 +1,10 @@
+# SPDX-License-Identifier: GPL-2.0
+
+CFLAGS += -I$(top_srcdir)/tools/include
+
+TEST_GEN_PROGS := pointer_masking
+
+include ../../lib.mk
+
+$(OUTPUT)/pointer_masking: pointer_masking.c
+	$(CC) -static -o$@ $(CFLAGS) $(LDFLAGS) $^
diff --git a/tools/testing/selftests/riscv/pm/pointer_masking.c b/tools/testing/selftests/riscv/pm/pointer_masking.c
new file mode 100644
index 000000000000..0fe80f963ace
--- /dev/null
+++ b/tools/testing/selftests/riscv/pm/pointer_masking.c
@@ -0,0 +1,330 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <errno.h>
+#include <fcntl.h>
+#include <setjmp.h>
+#include <signal.h>
+#include <stdbool.h>
+#include <sys/prctl.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include "../../kselftest.h"
+
+#ifndef PR_PMLEN_SHIFT
+#define PR_PMLEN_SHIFT			24
+#endif
+#ifndef PR_PMLEN_MASK
+#define PR_PMLEN_MASK			(0x7fUL << PR_PMLEN_SHIFT)
+#endif
+
+static int dev_zero;
+
+static int pipefd[2];
+
+static sigjmp_buf jmpbuf;
+
+static void sigsegv_handler(int sig)
+{
+	siglongjmp(jmpbuf, 1);
+}
+
+static int min_pmlen;
+static int max_pmlen;
+
+static inline bool valid_pmlen(int pmlen)
+{
+	return pmlen == 0 || pmlen == 7 || pmlen == 16;
+}
+
+static void test_pmlen(void)
+{
+	ksft_print_msg("Testing available PMLEN values\n");
+
+	for (int request = 0; request <= 16; request++) {
+		int pmlen, ret;
+
+		ret = prctl(PR_SET_TAGGED_ADDR_CTRL, request << PR_PMLEN_SHIFT, 0, 0, 0);
+		if (ret)
+			goto pr_set_error;
+
+		ret = prctl(PR_GET_TAGGED_ADDR_CTRL, 0, 0, 0, 0);
+		ksft_test_result(ret >= 0, "PMLEN=%d PR_GET_TAGGED_ADDR_CTRL\n", request);
+		if (ret < 0)
+			goto pr_get_error;
+
+		pmlen = (ret & PR_PMLEN_MASK) >> PR_PMLEN_SHIFT;
+		ksft_test_result(pmlen >= request, "PMLEN=%d constraint\n", request);
+		ksft_test_result(valid_pmlen(pmlen), "PMLEN=%d validity\n", request);
+
+		if (min_pmlen == 0)
+			min_pmlen = pmlen;
+		if (max_pmlen < pmlen)
+			max_pmlen = pmlen;
+
+		continue;
+
+pr_set_error:
+		ksft_test_result_skip("PMLEN=%d PR_GET_TAGGED_ADDR_CTRL\n", request);
+pr_get_error:
+		ksft_test_result_skip("PMLEN=%d constraint\n", request);
+		ksft_test_result_skip("PMLEN=%d validity\n", request);
+	}
+
+	if (max_pmlen == 0)
+		ksft_exit_fail_msg("Failed to enable pointer masking\n");
+}
+
+static int set_tagged_addr_ctrl(int pmlen, bool tagged_addr_abi)
+{
+	int arg, ret;
+
+	arg = pmlen << PR_PMLEN_SHIFT | tagged_addr_abi;
+	ret = prctl(PR_SET_TAGGED_ADDR_CTRL, arg, 0, 0, 0);
+	if (!ret) {
+		ret = prctl(PR_GET_TAGGED_ADDR_CTRL, 0, 0, 0, 0);
+		if (ret == arg)
+			return 0;
+	}
+
+	return ret < 0 ? -errno : -ENODATA;
+}
+
+static void test_dereference_pmlen(int pmlen)
+{
+	static volatile int i;
+	volatile int *p;
+	int ret;
+
+	ret = set_tagged_addr_ctrl(pmlen, false);
+	if (ret)
+		return ksft_test_result_error("PMLEN=%d setup (%d)\n", pmlen, ret);
+
+	i = pmlen;
+
+	if (pmlen) {
+		p = (volatile int *)((uintptr_t)&i | 1UL << __riscv_xlen - pmlen);
+
+		/* These dereferences should succeed. */
+		if (sigsetjmp(jmpbuf, 1))
+			return ksft_test_result_fail("PMLEN=%d valid tag\n", pmlen);
+		if (*p != pmlen)
+			return ksft_test_result_fail("PMLEN=%d bad value\n", pmlen);
+		*p++;
+	}
+
+	p = (volatile int *)((uintptr_t)&i | 1UL << __riscv_xlen - pmlen - 1);
+
+	/* These dereferences should raise SIGSEGV. */
+	if (sigsetjmp(jmpbuf, 1))
+		return ksft_test_result_pass("PMLEN=%d dereference\n", pmlen);
+	*p++;
+	ksft_test_result_fail("PMLEN=%d invalid tag\n", pmlen);
+}
+
+static void test_dereference(void)
+{
+	ksft_print_msg("Testing userspace pointer dereference\n");
+
+	signal(SIGSEGV, sigsegv_handler);
+
+	test_dereference_pmlen(0);
+	test_dereference_pmlen(min_pmlen);
+	test_dereference_pmlen(max_pmlen);
+
+	signal(SIGSEGV, SIG_DFL);
+}
+
+static void execve_child_sigsegv_handler(int sig)
+{
+	exit(42);
+}
+
+static int execve_child(void)
+{
+	static volatile int i;
+	volatile int *p = (volatile int *)((uintptr_t)&i | 1UL << __riscv_xlen - 7);
+
+	signal(SIGSEGV, execve_child_sigsegv_handler);
+
+	/* This dereference should raise SIGSEGV. */
+	return *p;
+}
+
+static void test_fork_exec(void)
+{
+	int ret, status;
+
+	ksft_print_msg("Testing fork/exec behavior\n");
+
+	ret = set_tagged_addr_ctrl(min_pmlen, false);
+	if (ret)
+		return ksft_test_result_error("setup (%d)\n", ret);
+
+	if (fork()) {
+		wait(&status);
+		ksft_test_result(WIFEXITED(status) && WEXITSTATUS(status) == 42,
+				 "dereference after fork\n");
+	} else {
+		static volatile int i = 42;
+		volatile int *p = (volatile int *)((uintptr_t)&i | 1UL << __riscv_xlen - min_pmlen);
+
+		/* This dereference should succeed. */
+		exit(*p);
+	}
+
+	if (fork()) {
+		wait(&status);
+		ksft_test_result(WIFEXITED(status) && WEXITSTATUS(status) == 42,
+				 "dereference after fork+exec\n");
+	} else {
+		/* Will call execve_child(). */
+		execve("/proc/self/exe", (char *const []) { "", NULL }, NULL);
+	}
+}
+
+static void test_tagged_addr_abi_sysctl(void)
+{
+	char value;
+	int fd;
+
+	ksft_print_msg("Testing tagged address ABI sysctl\n");
+
+	fd = open("/proc/sys/abi/tagged_addr_disabled", O_WRONLY);
+	if (fd < 0) {
+		ksft_test_result_skip("failed to open sysctl file\n");
+		ksft_test_result_skip("failed to open sysctl file\n");
+		return;
+	}
+
+	value = '1';
+	pwrite(fd, &value, 1, 0);
+	ksft_test_result(set_tagged_addr_ctrl(min_pmlen, true) == -EINVAL,
+			 "sysctl disabled\n");
+
+	value = '0';
+	pwrite(fd, &value, 1, 0);
+	ksft_test_result(set_tagged_addr_ctrl(min_pmlen, true) == 0,
+			 "sysctl enabled\n");
+
+	set_tagged_addr_ctrl(0, false);
+
+	close(fd);
+}
+
+static void test_tagged_addr_abi_pmlen(int pmlen)
+{
+	int i, *p, ret;
+
+	i = ~pmlen;
+
+	if (pmlen) {
+		p = (int *)((uintptr_t)&i | 1UL << __riscv_xlen - pmlen);
+
+		ret = set_tagged_addr_ctrl(pmlen, false);
+		if (ret)
+			return ksft_test_result_error("PMLEN=%d ABI disabled setup (%d)\n",
+						      pmlen, ret);
+
+		ret = write(pipefd[1], p, sizeof(*p));
+		if (ret >= 0 || errno != EFAULT)
+			return ksft_test_result_fail("PMLEN=%d ABI disabled write\n", pmlen);
+
+		ret = read(dev_zero, p, sizeof(*p));
+		if (ret >= 0 || errno != EFAULT)
+			return ksft_test_result_fail("PMLEN=%d ABI disabled read\n", pmlen);
+
+		if (i != ~pmlen)
+			return ksft_test_result_fail("PMLEN=%d ABI disabled value\n", pmlen);
+
+		ret = set_tagged_addr_ctrl(pmlen, true);
+		if (ret)
+			return ksft_test_result_error("PMLEN=%d ABI enabled setup (%d)\n",
+						      pmlen, ret);
+
+		ret = write(pipefd[1], p, sizeof(*p));
+		if (ret != sizeof(*p))
+			return ksft_test_result_fail("PMLEN=%d ABI enabled write\n", pmlen);
+
+		ret = read(dev_zero, p, sizeof(*p));
+		if (ret != sizeof(*p))
+			return ksft_test_result_fail("PMLEN=%d ABI enabled read\n", pmlen);
+
+		if (i)
+			return ksft_test_result_fail("PMLEN=%d ABI enabled value\n", pmlen);
+
+		i = ~pmlen;
+	} else {
+		/* The tagged address ABI cannot be enabled when PMLEN == 0. */
+		ret = set_tagged_addr_ctrl(pmlen, true);
+		if (ret != -EINVAL)
+			return ksft_test_result_error("PMLEN=%d ABI setup (%d)\n",
+						      pmlen, ret);
+	}
+
+	p = (int *)((uintptr_t)&i | 1UL << __riscv_xlen - pmlen - 1);
+
+	ret = write(pipefd[1], p, sizeof(*p));
+	if (ret >= 0 || errno != EFAULT)
+		return ksft_test_result_fail("PMLEN=%d invalid tag write (%d)\n", pmlen, errno);
+
+	ret = read(dev_zero, p, sizeof(*p));
+	if (ret >= 0 || errno != EFAULT)
+		return ksft_test_result_fail("PMLEN=%d invalid tag read\n", pmlen);
+
+	if (i != ~pmlen)
+		return ksft_test_result_fail("PMLEN=%d invalid tag value\n", pmlen);
+
+	ksft_test_result_pass("PMLEN=%d tagged address ABI\n", pmlen);
+}
+
+static void test_tagged_addr_abi(void)
+{
+	ksft_print_msg("Testing tagged address ABI\n");
+
+	test_tagged_addr_abi_pmlen(0);
+	test_tagged_addr_abi_pmlen(min_pmlen);
+	test_tagged_addr_abi_pmlen(max_pmlen);
+}
+
+static struct test_info {
+	unsigned int nr_tests;
+	void (*test_fn)(void);
+} tests[] = {
+	{ .nr_tests = 17 * 3, test_pmlen },
+	{ .nr_tests = 3, test_dereference },
+	{ .nr_tests = 2, test_fork_exec },
+	{ .nr_tests = 2, test_tagged_addr_abi_sysctl },
+	{ .nr_tests = 3, test_tagged_addr_abi },
+};
+
+int main(int argc, char **argv)
+{
+	unsigned int plan = 0;
+	int ret;
+
+	/* Check if this is the child process after execve(). */
+	if (!argv[0][0])
+		return execve_child();
+
+	dev_zero = open("/dev/zero", O_RDWR);
+	if (dev_zero < 0)
+		return 1;
+
+	/* Write to a pipe so the kernel must dereference the buffer pointer. */
+	ret = pipe(pipefd);
+	if (ret)
+		return 1;
+
+	ksft_print_header();
+
+	for (int i = 0; i < ARRAY_SIZE(tests); ++i)
+		plan += tests[i].nr_tests;
+
+	ksft_set_plan(plan);
+
+	for (int i = 0; i < ARRAY_SIZE(tests); ++i)
+		tests[i].test_fn();
+
+	ksft_finished();
+}
-- 
2.45.1

[PATCH v3 08/10] riscv: hwprobe: Export the Supm ISA extension

[Samuel Holland]

Supm is a virtual ISA extension defined in the RISC-V Pointer Masking
specification, which indicates that pointer masking is available in
U-mode. It can be provided by either Smnpm or Ssnpm, depending on which
mode the kernel runs in. Userspace should not care about this
distinction, so export Supm instead of either underlying extension.

Hide the extension if the kernel was compiled without support for the
pointer masking prctl() interface.

Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
---

(no changes since v2)

Changes in v2:
 - New patch for v2

 Documentation/arch/riscv/hwprobe.rst  | 3 +++
 arch/riscv/include/uapi/asm/hwprobe.h | 1 +
 arch/riscv/kernel/sys_hwprobe.c       | 3 +++
 3 files changed, 7 insertions(+)

diff --git a/Documentation/arch/riscv/hwprobe.rst b/Documentation/arch/riscv/hwprobe.rst
index 3db60a0911df..a6d725b9d138 100644
--- a/Documentation/arch/riscv/hwprobe.rst
+++ b/Documentation/arch/riscv/hwprobe.rst
@@ -239,6 +239,9 @@ The following keys are defined:
        ratified in commit 98918c844281 ("Merge pull request #1217 from
        riscv/zawrs") of riscv-isa-manual.
 
+  * :c:macro:`RISCV_HWPROBE_EXT_SUPM`: The Supm extension is supported as
+       defined in version 1.0.0-rc2 of the RISC-V Pointer Masking manual.
+
 * :c:macro:`RISCV_HWPROBE_KEY_CPUPERF_0`: A bitmask that contains performance
   information about the selected set of processors.
 
diff --git a/arch/riscv/include/uapi/asm/hwprobe.h b/arch/riscv/include/uapi/asm/hwprobe.h
index b706c8e47b02..6fdaefa62e14 100644
--- a/arch/riscv/include/uapi/asm/hwprobe.h
+++ b/arch/riscv/include/uapi/asm/hwprobe.h
@@ -72,6 +72,7 @@ struct riscv_hwprobe {
 #define		RISCV_HWPROBE_EXT_ZCF		(1ULL << 46)
 #define		RISCV_HWPROBE_EXT_ZCMOP		(1ULL << 47)
 #define		RISCV_HWPROBE_EXT_ZAWRS		(1ULL << 48)
+#define		RISCV_HWPROBE_EXT_SUPM		(1ULL << 49)
 #define RISCV_HWPROBE_KEY_CPUPERF_0	5
 #define		RISCV_HWPROBE_MISALIGNED_UNKNOWN	(0 << 0)
 #define		RISCV_HWPROBE_MISALIGNED_EMULATED	(1 << 0)
diff --git a/arch/riscv/kernel/sys_hwprobe.c b/arch/riscv/kernel/sys_hwprobe.c
index 8d1b5c35d2a7..b6497dc0e7f1 100644
--- a/arch/riscv/kernel/sys_hwprobe.c
+++ b/arch/riscv/kernel/sys_hwprobe.c
@@ -150,6 +150,9 @@ static void hwprobe_isa_ext0(struct riscv_hwprobe *pair,
 			EXT_KEY(ZFH);
 			EXT_KEY(ZFHMIN);
 		}
+
+		if (IS_ENABLED(CONFIG_RISCV_ISA_SUPM))
+			EXT_KEY(SUPM);
 #undef EXT_KEY
 	}
 
-- 
2.45.1

[PATCH v3 09/10] RISC-V: KVM: Allow Smnpm and Ssnpm extensions for guests

[Samuel Holland]

The interface for controlling pointer masking in VS-mode is henvcfg.PMM,
which is part of the Ssnpm extension, even though pointer masking in
HS-mode is provided by the Smnpm extension. As a result, emulating Smnpm
in the guest requires (only) Ssnpm on the host.

Since the guest configures Smnpm through the SBI Firmware Features
interface, the extension can be disabled by failing the SBI call. Ssnpm
cannot be disabled without intercepting writes to the senvcfg CSR.

Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
---

(no changes since v2)

Changes in v2:
 - New patch for v2

 arch/riscv/include/uapi/asm/kvm.h | 2 ++
 arch/riscv/kvm/vcpu_onereg.c      | 3 +++
 2 files changed, 5 insertions(+)

diff --git a/arch/riscv/include/uapi/asm/kvm.h b/arch/riscv/include/uapi/asm/kvm.h
index e97db3296456..4f24201376b1 100644
--- a/arch/riscv/include/uapi/asm/kvm.h
+++ b/arch/riscv/include/uapi/asm/kvm.h
@@ -175,6 +175,8 @@ enum KVM_RISCV_ISA_EXT_ID {
 	KVM_RISCV_ISA_EXT_ZCF,
 	KVM_RISCV_ISA_EXT_ZCMOP,
 	KVM_RISCV_ISA_EXT_ZAWRS,
+	KVM_RISCV_ISA_EXT_SMNPM,
+	KVM_RISCV_ISA_EXT_SSNPM,
 	KVM_RISCV_ISA_EXT_MAX,
 };
 
diff --git a/arch/riscv/kvm/vcpu_onereg.c b/arch/riscv/kvm/vcpu_onereg.c
index b319c4c13c54..6f833ec2344a 100644
--- a/arch/riscv/kvm/vcpu_onereg.c
+++ b/arch/riscv/kvm/vcpu_onereg.c
@@ -34,9 +34,11 @@ static const unsigned long kvm_isa_ext_arr[] = {
 	[KVM_RISCV_ISA_EXT_M] = RISCV_ISA_EXT_m,
 	[KVM_RISCV_ISA_EXT_V] = RISCV_ISA_EXT_v,
 	/* Multi letter extensions (alphabetically sorted) */
+	[KVM_RISCV_ISA_EXT_SMNPM] = RISCV_ISA_EXT_SSNPM,
 	KVM_ISA_EXT_ARR(SMSTATEEN),
 	KVM_ISA_EXT_ARR(SSAIA),
 	KVM_ISA_EXT_ARR(SSCOFPMF),
+	KVM_ISA_EXT_ARR(SSNPM),
 	KVM_ISA_EXT_ARR(SSTC),
 	KVM_ISA_EXT_ARR(SVINVAL),
 	KVM_ISA_EXT_ARR(SVNAPOT),
@@ -129,6 +131,7 @@ static bool kvm_riscv_vcpu_isa_disable_allowed(unsigned long ext)
 	case KVM_RISCV_ISA_EXT_M:
 	/* There is not architectural config bit to disable sscofpmf completely */
 	case KVM_RISCV_ISA_EXT_SSCOFPMF:
+	case KVM_RISCV_ISA_EXT_SSNPM:
 	case KVM_RISCV_ISA_EXT_SSTC:
 	case KVM_RISCV_ISA_EXT_SVINVAL:
 	case KVM_RISCV_ISA_EXT_SVNAPOT:
-- 
2.45.1

[PATCH v3 10/10] KVM: riscv: selftests: Add Smnpm and Ssnpm to get-reg-list test

[Samuel Holland]

Add testing for the pointer masking extensions exposed to KVM guests.

Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
---

(no changes since v2)

Changes in v2:
 - New patch for v2

 tools/testing/selftests/kvm/riscv/get-reg-list.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/tools/testing/selftests/kvm/riscv/get-reg-list.c b/tools/testing/selftests/kvm/riscv/get-reg-list.c
index 8e34f7fa44e9..54ab484d0000 100644
--- a/tools/testing/selftests/kvm/riscv/get-reg-list.c
+++ b/tools/testing/selftests/kvm/riscv/get-reg-list.c
@@ -41,9 +41,11 @@ bool filter_reg(__u64 reg)
 	case KVM_REG_RISCV_ISA_EXT | KVM_REG_RISCV_ISA_SINGLE | KVM_RISCV_ISA_EXT_I:
 	case KVM_REG_RISCV_ISA_EXT | KVM_REG_RISCV_ISA_SINGLE | KVM_RISCV_ISA_EXT_M:
 	case KVM_REG_RISCV_ISA_EXT | KVM_REG_RISCV_ISA_SINGLE | KVM_RISCV_ISA_EXT_V:
+	case KVM_REG_RISCV_ISA_EXT | KVM_REG_RISCV_ISA_SINGLE | KVM_RISCV_ISA_EXT_SMNPM:
 	case KVM_REG_RISCV_ISA_EXT | KVM_REG_RISCV_ISA_SINGLE | KVM_RISCV_ISA_EXT_SMSTATEEN:
 	case KVM_REG_RISCV_ISA_EXT | KVM_REG_RISCV_ISA_SINGLE | KVM_RISCV_ISA_EXT_SSAIA:
 	case KVM_REG_RISCV_ISA_EXT | KVM_REG_RISCV_ISA_SINGLE | KVM_RISCV_ISA_EXT_SSCOFPMF:
+	case KVM_REG_RISCV_ISA_EXT | KVM_REG_RISCV_ISA_SINGLE | KVM_RISCV_ISA_EXT_SSNPM:
 	case KVM_REG_RISCV_ISA_EXT | KVM_REG_RISCV_ISA_SINGLE | KVM_RISCV_ISA_EXT_SSTC:
 	case KVM_REG_RISCV_ISA_EXT | KVM_REG_RISCV_ISA_SINGLE | KVM_RISCV_ISA_EXT_SVINVAL:
 	case KVM_REG_RISCV_ISA_EXT | KVM_REG_RISCV_ISA_SINGLE | KVM_RISCV_ISA_EXT_SVNAPOT:
@@ -414,9 +416,11 @@ static const char *isa_ext_single_id_to_str(__u64 reg_off)
 		KVM_ISA_EXT_ARR(I),
 		KVM_ISA_EXT_ARR(M),
 		KVM_ISA_EXT_ARR(V),
+		KVM_ISA_EXT_ARR(SMNPM),
 		KVM_ISA_EXT_ARR(SMSTATEEN),
 		KVM_ISA_EXT_ARR(SSAIA),
 		KVM_ISA_EXT_ARR(SSCOFPMF),
+		KVM_ISA_EXT_ARR(SSNPM),
 		KVM_ISA_EXT_ARR(SSTC),
 		KVM_ISA_EXT_ARR(SVINVAL),
 		KVM_ISA_EXT_ARR(SVNAPOT),
@@ -946,8 +950,10 @@ KVM_ISA_EXT_SUBLIST_CONFIG(aia, AIA);
 KVM_ISA_EXT_SUBLIST_CONFIG(fp_f, FP_F);
 KVM_ISA_EXT_SUBLIST_CONFIG(fp_d, FP_D);
 KVM_ISA_EXT_SIMPLE_CONFIG(h, H);
+KVM_ISA_EXT_SIMPLE_CONFIG(smnpm, SMNPM);
 KVM_ISA_EXT_SUBLIST_CONFIG(smstateen, SMSTATEEN);
 KVM_ISA_EXT_SIMPLE_CONFIG(sscofpmf, SSCOFPMF);
+KVM_ISA_EXT_SIMPLE_CONFIG(ssnpm, SSNPM);
 KVM_ISA_EXT_SIMPLE_CONFIG(sstc, SSTC);
 KVM_ISA_EXT_SIMPLE_CONFIG(svinval, SVINVAL);
 KVM_ISA_EXT_SIMPLE_CONFIG(svnapot, SVNAPOT);
@@ -1009,8 +1015,10 @@ struct vcpu_reg_list *vcpu_configs[] = {
 	&config_fp_f,
 	&config_fp_d,
 	&config_h,
+	&config_smnpm,
 	&config_smstateen,
 	&config_sscofpmf,
+	&config_ssnpm,
 	&config_sstc,
 	&config_svinval,
 	&config_svnapot,
-- 
2.45.1

Re: [PATCH v3 05/10] riscv: Add support for the tagged address ABI

[Alexandre Ghiti]

On 14/08/2024 10:13, Samuel Holland wrote:
> When pointer masking is enabled for userspace, the kernel can accept
> tagged pointers as arguments to some system calls. Allow this by
> untagging the pointers in access_ok() and the uaccess routines. The
> uaccess routines must peform untagging in software because U-mode and
> S-mode have entirely separate pointer masking configurations. In fact,
> hardware may not even implement pointer masking for S-mode.
>
> Since the number of tag bits is variable, untagged_addr_remote() needs
> to know what PMLEN to use for the remote mm. Therefore, the pointer
> masking mode must be the same for all threads sharing an mm. Enforce
> this with a lock flag in the mm context, as x86 does for LAM. The flag
> gets reset in init_new_context() during fork(), as the new mm is no
> longer multithreaded.
>
> Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
> ---
>
> Changes in v3:
>   - Use IS_ENABLED instead of #ifdef when possible
>   - Implement mm_untag_mask()
>   - Remove pmlen from struct thread_info (now only in mm_context_t)
>
> Changes in v2:
>   - Implement untagged_addr_remote()
>   - Restrict PMLEN changes once a process is multithreaded
>
>   arch/riscv/include/asm/mmu.h         |  7 +++
>   arch/riscv/include/asm/mmu_context.h | 13 +++++
>   arch/riscv/include/asm/uaccess.h     | 58 ++++++++++++++++++++--
>   arch/riscv/kernel/process.c          | 73 ++++++++++++++++++++++++++--
>   4 files changed, 141 insertions(+), 10 deletions(-)
>
> diff --git a/arch/riscv/include/asm/mmu.h b/arch/riscv/include/asm/mmu.h
> index c9e03e9da3dc..1cc90465d75b 100644
> --- a/arch/riscv/include/asm/mmu.h
> +++ b/arch/riscv/include/asm/mmu.h
> @@ -25,9 +25,16 @@ typedef struct {
>   #ifdef CONFIG_BINFMT_ELF_FDPIC
>   	unsigned long exec_fdpic_loadmap;
>   	unsigned long interp_fdpic_loadmap;
> +#endif
> +	unsigned long flags;
> +#ifdef CONFIG_RISCV_ISA_SUPM
> +	u8 pmlen;
>   #endif
>   } mm_context_t;
>   
> +/* Lock the pointer masking mode because this mm is multithreaded */
> +#define MM_CONTEXT_LOCK_PMLEN	0
> +
>   #define cntx2asid(cntx)		((cntx) & SATP_ASID_MASK)
>   #define cntx2version(cntx)	((cntx) & ~SATP_ASID_MASK)
>   
> diff --git a/arch/riscv/include/asm/mmu_context.h b/arch/riscv/include/asm/mmu_context.h
> index 7030837adc1a..8c4bc49a3a0f 100644
> --- a/arch/riscv/include/asm/mmu_context.h
> +++ b/arch/riscv/include/asm/mmu_context.h
> @@ -20,6 +20,9 @@ void switch_mm(struct mm_struct *prev, struct mm_struct *next,
>   static inline void activate_mm(struct mm_struct *prev,
>   			       struct mm_struct *next)
>   {
> +#ifdef CONFIG_RISCV_ISA_SUPM
> +	next->context.pmlen = 0;
> +#endif
>   	switch_mm(prev, next, NULL);
>   }
>   
> @@ -30,11 +33,21 @@ static inline int init_new_context(struct task_struct *tsk,
>   #ifdef CONFIG_MMU
>   	atomic_long_set(&mm->context.id, 0);
>   #endif
> +	if (IS_ENABLED(CONFIG_RISCV_ISA_SUPM))
> +		clear_bit(MM_CONTEXT_LOCK_PMLEN, &mm->context.flags);
>   	return 0;
>   }
>   
>   DECLARE_STATIC_KEY_FALSE(use_asid_allocator);
>   
> +#ifdef CONFIG_RISCV_ISA_SUPM
> +#define mm_untag_mask mm_untag_mask
> +static inline unsigned long mm_untag_mask(struct mm_struct *mm)
> +{
> +	return -1UL >> mm->context.pmlen;
> +}
> +#endif
> +
>   #include <asm-generic/mmu_context.h>
>   
>   #endif /* _ASM_RISCV_MMU_CONTEXT_H */
> diff --git a/arch/riscv/include/asm/uaccess.h b/arch/riscv/include/asm/uaccess.h
> index 72ec1d9bd3f3..6416559232a2 100644
> --- a/arch/riscv/include/asm/uaccess.h
> +++ b/arch/riscv/include/asm/uaccess.h
> @@ -9,8 +9,56 @@
>   #define _ASM_RISCV_UACCESS_H
>   
>   #include <asm/asm-extable.h>
> +#include <asm/cpufeature.h>
>   #include <asm/pgtable.h>		/* for TASK_SIZE */
>   
> +#ifdef CONFIG_RISCV_ISA_SUPM
> +static inline unsigned long __untagged_addr(unsigned long addr)
> +{
> +	if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM)) {
> +		u8 pmlen = current->mm->context.pmlen;
> +
> +		/* Virtual addresses are sign-extended; physical addresses are zero-extended. */
> +		if (IS_ENABLED(CONFIG_MMU))
> +			return (long)(addr << pmlen) >> pmlen;
> +		else
> +			return (addr << pmlen) >> pmlen;
> +	}
> +
> +	return addr;
> +}
> +
> +#define untagged_addr(addr) ({						\
> +	unsigned long __addr = (__force unsigned long)(addr);		\
> +	(__force __typeof__(addr))__untagged_addr(__addr);		\
> +})
> +
> +static inline unsigned long __untagged_addr_remote(struct mm_struct *mm, unsigned long addr)
> +{
> +	if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM)) {
> +		u8 pmlen = mm->context.pmlen;
> +
> +		/* Virtual addresses are sign-extended; physical addresses are zero-extended. */
> +		if (IS_ENABLED(CONFIG_MMU))
> +			return (long)(addr << pmlen) >> pmlen;
> +		else
> +			return (addr << pmlen) >> pmlen;
> +	}
> +
> +	return addr;
> +}


I should have mentioned that in v2: now that you removed the thread_info 
pmlen field, __untagged_addr_remote() and __untagged_addr() are almost 
the same, can you merge them?

Thanks!

Alex


> +
> +#define untagged_addr_remote(mm, addr) ({				\
> +	unsigned long __addr = (__force unsigned long)(addr);		\
> +	mmap_assert_locked(mm);						\
> +	(__force __typeof__(addr))__untagged_addr_remote(mm, __addr);	\
> +})
> +
> +#define access_ok(addr, size) likely(__access_ok(untagged_addr(addr), size))
> +#else
> +#define untagged_addr(addr) (addr)
> +#endif
> +
>   /*
>    * User space memory access functions
>    */
> @@ -130,7 +178,7 @@ do {								\
>    */
>   #define __get_user(x, ptr)					\
>   ({								\
> -	const __typeof__(*(ptr)) __user *__gu_ptr = (ptr);	\
> +	const __typeof__(*(ptr)) __user *__gu_ptr = untagged_addr(ptr); \
>   	long __gu_err = 0;					\
>   								\
>   	__chk_user_ptr(__gu_ptr);				\
> @@ -246,7 +294,7 @@ do {								\
>    */
>   #define __put_user(x, ptr)					\
>   ({								\
> -	__typeof__(*(ptr)) __user *__gu_ptr = (ptr);		\
> +	__typeof__(*(ptr)) __user *__gu_ptr = untagged_addr(ptr); \
>   	__typeof__(*__gu_ptr) __val = (x);			\
>   	long __pu_err = 0;					\
>   								\
> @@ -293,13 +341,13 @@ unsigned long __must_check __asm_copy_from_user(void *to,
>   static inline unsigned long
>   raw_copy_from_user(void *to, const void __user *from, unsigned long n)
>   {
> -	return __asm_copy_from_user(to, from, n);
> +	return __asm_copy_from_user(to, untagged_addr(from), n);
>   }
>   
>   static inline unsigned long
>   raw_copy_to_user(void __user *to, const void *from, unsigned long n)
>   {
> -	return __asm_copy_to_user(to, from, n);
> +	return __asm_copy_to_user(untagged_addr(to), from, n);
>   }
>   
>   extern long strncpy_from_user(char *dest, const char __user *src, long count);
> @@ -314,7 +362,7 @@ unsigned long __must_check clear_user(void __user *to, unsigned long n)
>   {
>   	might_fault();
>   	return access_ok(to, n) ?
> -		__clear_user(to, n) : n;
> +		__clear_user(untagged_addr(to), n) : n;
>   }
>   
>   #define __get_kernel_nofault(dst, src, type, err_label)			\
> diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
> index 1280a7c4a412..f4d8e5c3bb84 100644
> --- a/arch/riscv/kernel/process.c
> +++ b/arch/riscv/kernel/process.c
> @@ -203,6 +203,10 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
>   	unsigned long tls = args->tls;
>   	struct pt_regs *childregs = task_pt_regs(p);
>   
> +	/* Ensure all threads in this mm have the same pointer masking mode. */
> +	if (IS_ENABLED(CONFIG_RISCV_ISA_SUPM) && p->mm && (clone_flags & CLONE_VM))
> +		set_bit(MM_CONTEXT_LOCK_PMLEN, &p->mm->context.flags);
> +
>   	memset(&p->thread.s, 0, sizeof(p->thread.s));
>   
>   	/* p->thread holds context to be restored by __switch_to() */
> @@ -248,10 +252,16 @@ enum {
>   static bool have_user_pmlen_7;
>   static bool have_user_pmlen_16;
>   
> +/*
> + * Control the relaxed ABI allowing tagged user addresses into the kernel.
> + */
> +static unsigned int tagged_addr_disabled;
> +
>   long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg)
>   {
> -	unsigned long valid_mask = PR_PMLEN_MASK;
> +	unsigned long valid_mask = PR_PMLEN_MASK | PR_TAGGED_ADDR_ENABLE;
>   	struct thread_info *ti = task_thread_info(task);
> +	struct mm_struct *mm = task->mm;
>   	unsigned long pmm;
>   	u8 pmlen;
>   
> @@ -266,16 +276,41 @@ long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg)
>   	 * in case choosing a larger PMLEN has a performance impact.
>   	 */
>   	pmlen = FIELD_GET(PR_PMLEN_MASK, arg);
> -	if (pmlen == PMLEN_0)
> +	if (pmlen == PMLEN_0) {
>   		pmm = ENVCFG_PMM_PMLEN_0;
> -	else if (pmlen <= PMLEN_7 && have_user_pmlen_7)
> +	} else if (pmlen <= PMLEN_7 && have_user_pmlen_7) {
> +		pmlen = PMLEN_7;
>   		pmm = ENVCFG_PMM_PMLEN_7;
> -	else if (pmlen <= PMLEN_16 && have_user_pmlen_16)
> +	} else if (pmlen <= PMLEN_16 && have_user_pmlen_16) {
> +		pmlen = PMLEN_16;
>   		pmm = ENVCFG_PMM_PMLEN_16;
> -	else
> +	} else {
>   		return -EINVAL;
> +	}
> +
> +	/*
> +	 * Do not allow the enabling of the tagged address ABI if globally
> +	 * disabled via sysctl abi.tagged_addr_disabled, if pointer masking
> +	 * is disabled for userspace.
> +	 */
> +	if (arg & PR_TAGGED_ADDR_ENABLE && (tagged_addr_disabled || !pmlen))
> +		return -EINVAL;
> +
> +	if (!(arg & PR_TAGGED_ADDR_ENABLE))
> +		pmlen = PMLEN_0;
> +
> +	if (mmap_write_lock_killable(mm))
> +		return -EINTR;
> +
> +	if (test_bit(MM_CONTEXT_LOCK_PMLEN, &mm->context.flags) && mm->context.pmlen != pmlen) {
> +		mmap_write_unlock(mm);
> +		return -EBUSY;
> +	}
>   
>   	envcfg_update_bits(task, ENVCFG_PMM, pmm);
> +	mm->context.pmlen = pmlen;
> +
> +	mmap_write_unlock(mm);
>   
>   	return 0;
>   }
> @@ -288,6 +323,10 @@ long get_tagged_addr_ctrl(struct task_struct *task)
>   	if (is_compat_thread(ti))
>   		return -EINVAL;
>   
> +	/*
> +	 * The mm context's pmlen is set only when the tagged address ABI is
> +	 * enabled, so the effective PMLEN must be extracted from envcfg.PMM.
> +	 */
>   	switch (task->thread.envcfg & ENVCFG_PMM) {
>   	case ENVCFG_PMM_PMLEN_7:
>   		ret = FIELD_PREP(PR_PMLEN_MASK, PMLEN_7);
> @@ -297,6 +336,9 @@ long get_tagged_addr_ctrl(struct task_struct *task)
>   		break;
>   	}
>   
> +	if (task->mm->context.pmlen)
> +		ret |= PR_TAGGED_ADDR_ENABLE;
> +
>   	return ret;
>   }
>   
> @@ -306,6 +348,24 @@ static bool try_to_set_pmm(unsigned long value)
>   	return (csr_read_clear(CSR_ENVCFG, ENVCFG_PMM) & ENVCFG_PMM) == value;
>   }
>   
> +/*
> + * Global sysctl to disable the tagged user addresses support. This control
> + * only prevents the tagged address ABI enabling via prctl() and does not
> + * disable it for tasks that already opted in to the relaxed ABI.
> + */
> +
> +static struct ctl_table tagged_addr_sysctl_table[] = {
> +	{
> +		.procname	= "tagged_addr_disabled",
> +		.mode		= 0644,
> +		.data		= &tagged_addr_disabled,
> +		.maxlen		= sizeof(int),
> +		.proc_handler	= proc_dointvec_minmax,
> +		.extra1		= SYSCTL_ZERO,
> +		.extra2		= SYSCTL_ONE,
> +	},
> +};
> +
>   static int __init tagged_addr_init(void)
>   {
>   	if (!riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM))
> @@ -319,6 +379,9 @@ static int __init tagged_addr_init(void)
>   	have_user_pmlen_7 = try_to_set_pmm(ENVCFG_PMM_PMLEN_7);
>   	have_user_pmlen_16 = try_to_set_pmm(ENVCFG_PMM_PMLEN_16);
>   
> +	if (!register_sysctl("abi", tagged_addr_sysctl_table))
> +		return -EINVAL;
> +
>   	return 0;
>   }
>   core_initcall(tagged_addr_init);

Re: [PATCH v3 05/10] riscv: Add support for the tagged address ABI

[Samuel Holland]

Hi Alex,

On 2024-08-14 10:10 AM, Alexandre Ghiti wrote:
> On 14/08/2024 10:13, Samuel Holland wrote:
>> When pointer masking is enabled for userspace, the kernel can accept
>> tagged pointers as arguments to some system calls. Allow this by
>> untagging the pointers in access_ok() and the uaccess routines. The
>> uaccess routines must peform untagging in software because U-mode and
>> S-mode have entirely separate pointer masking configurations. In fact,
>> hardware may not even implement pointer masking for S-mode.
>>
>> Since the number of tag bits is variable, untagged_addr_remote() needs
>> to know what PMLEN to use for the remote mm. Therefore, the pointer
>> masking mode must be the same for all threads sharing an mm. Enforce
>> this with a lock flag in the mm context, as x86 does for LAM. The flag
>> gets reset in init_new_context() during fork(), as the new mm is no
>> longer multithreaded.
>>
>> Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
>> ---
>>
>> Changes in v3:
>>   - Use IS_ENABLED instead of #ifdef when possible
>>   - Implement mm_untag_mask()
>>   - Remove pmlen from struct thread_info (now only in mm_context_t)
>>
>> Changes in v2:
>>   - Implement untagged_addr_remote()
>>   - Restrict PMLEN changes once a process is multithreaded
>>
>>   arch/riscv/include/asm/mmu.h         |  7 +++
>>   arch/riscv/include/asm/mmu_context.h | 13 +++++
>>   arch/riscv/include/asm/uaccess.h     | 58 ++++++++++++++++++++--
>>   arch/riscv/kernel/process.c          | 73 ++++++++++++++++++++++++++--
>>   4 files changed, 141 insertions(+), 10 deletions(-)
>>
>> diff --git a/arch/riscv/include/asm/mmu.h b/arch/riscv/include/asm/mmu.h
>> index c9e03e9da3dc..1cc90465d75b 100644
>> --- a/arch/riscv/include/asm/mmu.h
>> +++ b/arch/riscv/include/asm/mmu.h
>> @@ -25,9 +25,16 @@ typedef struct {
>>   #ifdef CONFIG_BINFMT_ELF_FDPIC
>>       unsigned long exec_fdpic_loadmap;
>>       unsigned long interp_fdpic_loadmap;
>> +#endif
>> +    unsigned long flags;
>> +#ifdef CONFIG_RISCV_ISA_SUPM
>> +    u8 pmlen;
>>   #endif
>>   } mm_context_t;
>>   +/* Lock the pointer masking mode because this mm is multithreaded */
>> +#define MM_CONTEXT_LOCK_PMLEN    0
>> +
>>   #define cntx2asid(cntx)        ((cntx) & SATP_ASID_MASK)
>>   #define cntx2version(cntx)    ((cntx) & ~SATP_ASID_MASK)
>>   diff --git a/arch/riscv/include/asm/mmu_context.h
>> b/arch/riscv/include/asm/mmu_context.h
>> index 7030837adc1a..8c4bc49a3a0f 100644
>> --- a/arch/riscv/include/asm/mmu_context.h
>> +++ b/arch/riscv/include/asm/mmu_context.h
>> @@ -20,6 +20,9 @@ void switch_mm(struct mm_struct *prev, struct mm_struct *next,
>>   static inline void activate_mm(struct mm_struct *prev,
>>                      struct mm_struct *next)
>>   {
>> +#ifdef CONFIG_RISCV_ISA_SUPM
>> +    next->context.pmlen = 0;
>> +#endif
>>       switch_mm(prev, next, NULL);
>>   }
>>   @@ -30,11 +33,21 @@ static inline int init_new_context(struct task_struct *tsk,
>>   #ifdef CONFIG_MMU
>>       atomic_long_set(&mm->context.id, 0);
>>   #endif
>> +    if (IS_ENABLED(CONFIG_RISCV_ISA_SUPM))
>> +        clear_bit(MM_CONTEXT_LOCK_PMLEN, &mm->context.flags);
>>       return 0;
>>   }
>>     DECLARE_STATIC_KEY_FALSE(use_asid_allocator);
>>   +#ifdef CONFIG_RISCV_ISA_SUPM
>> +#define mm_untag_mask mm_untag_mask
>> +static inline unsigned long mm_untag_mask(struct mm_struct *mm)
>> +{
>> +    return -1UL >> mm->context.pmlen;
>> +}
>> +#endif
>> +
>>   #include <asm-generic/mmu_context.h>
>>     #endif /* _ASM_RISCV_MMU_CONTEXT_H */
>> diff --git a/arch/riscv/include/asm/uaccess.h b/arch/riscv/include/asm/uaccess.h
>> index 72ec1d9bd3f3..6416559232a2 100644
>> --- a/arch/riscv/include/asm/uaccess.h
>> +++ b/arch/riscv/include/asm/uaccess.h
>> @@ -9,8 +9,56 @@
>>   #define _ASM_RISCV_UACCESS_H
>>     #include <asm/asm-extable.h>
>> +#include <asm/cpufeature.h>
>>   #include <asm/pgtable.h>        /* for TASK_SIZE */
>>   +#ifdef CONFIG_RISCV_ISA_SUPM
>> +static inline unsigned long __untagged_addr(unsigned long addr)
>> +{
>> +    if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM)) {
>> +        u8 pmlen = current->mm->context.pmlen;
>> +
>> +        /* Virtual addresses are sign-extended; physical addresses are
>> zero-extended. */
>> +        if (IS_ENABLED(CONFIG_MMU))
>> +            return (long)(addr << pmlen) >> pmlen;
>> +        else
>> +            return (addr << pmlen) >> pmlen;
>> +    }
>> +
>> +    return addr;
>> +}
>> +
>> +#define untagged_addr(addr) ({                        \
>> +    unsigned long __addr = (__force unsigned long)(addr);        \
>> +    (__force __typeof__(addr))__untagged_addr(__addr);        \
>> +})
>> +
>> +static inline unsigned long __untagged_addr_remote(struct mm_struct *mm,
>> unsigned long addr)
>> +{
>> +    if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM)) {
>> +        u8 pmlen = mm->context.pmlen;
>> +
>> +        /* Virtual addresses are sign-extended; physical addresses are
>> zero-extended. */
>> +        if (IS_ENABLED(CONFIG_MMU))
>> +            return (long)(addr << pmlen) >> pmlen;
>> +        else
>> +            return (addr << pmlen) >> pmlen;
>> +    }
>> +
>> +    return addr;
>> +}
> 
> 
> I should have mentioned that in v2: now that you removed the thread_info pmlen
> field, __untagged_addr_remote() and __untagged_addr() are almost the same, can
> you merge them?

I can merge them, but this places the load of current->mm outside the static
branch. If you think that is okay, then I'll merge them for v4.

Regards,
Samuel

>> +
>> +#define untagged_addr_remote(mm, addr) ({                \
>> +    unsigned long __addr = (__force unsigned long)(addr);        \
>> +    mmap_assert_locked(mm);                        \
>> +    (__force __typeof__(addr))__untagged_addr_remote(mm, __addr);    \
>> +})
>> +
>> +#define access_ok(addr, size) likely(__access_ok(untagged_addr(addr), size))
>> +#else
>> +#define untagged_addr(addr) (addr)
>> +#endif
>> +
>>   /*
>>    * User space memory access functions
>>    */
>> @@ -130,7 +178,7 @@ do {                                \
>>    */
>>   #define __get_user(x, ptr)                    \
>>   ({                                \
>> -    const __typeof__(*(ptr)) __user *__gu_ptr = (ptr);    \
>> +    const __typeof__(*(ptr)) __user *__gu_ptr = untagged_addr(ptr); \
>>       long __gu_err = 0;                    \
>>                                   \
>>       __chk_user_ptr(__gu_ptr);                \
>> @@ -246,7 +294,7 @@ do {                                \
>>    */
>>   #define __put_user(x, ptr)                    \
>>   ({                                \
>> -    __typeof__(*(ptr)) __user *__gu_ptr = (ptr);        \
>> +    __typeof__(*(ptr)) __user *__gu_ptr = untagged_addr(ptr); \
>>       __typeof__(*__gu_ptr) __val = (x);            \
>>       long __pu_err = 0;                    \
>>                                   \
>> @@ -293,13 +341,13 @@ unsigned long __must_check __asm_copy_from_user(void *to,
>>   static inline unsigned long
>>   raw_copy_from_user(void *to, const void __user *from, unsigned long n)
>>   {
>> -    return __asm_copy_from_user(to, from, n);
>> +    return __asm_copy_from_user(to, untagged_addr(from), n);
>>   }
>>     static inline unsigned long
>>   raw_copy_to_user(void __user *to, const void *from, unsigned long n)
>>   {
>> -    return __asm_copy_to_user(to, from, n);
>> +    return __asm_copy_to_user(untagged_addr(to), from, n);
>>   }
>>     extern long strncpy_from_user(char *dest, const char __user *src, long
>> count);
>> @@ -314,7 +362,7 @@ unsigned long __must_check clear_user(void __user *to,
>> unsigned long n)
>>   {
>>       might_fault();
>>       return access_ok(to, n) ?
>> -        __clear_user(to, n) : n;
>> +        __clear_user(untagged_addr(to), n) : n;
>>   }
>>     #define __get_kernel_nofault(dst, src, type, err_label)            \
>> diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
>> index 1280a7c4a412..f4d8e5c3bb84 100644
>> --- a/arch/riscv/kernel/process.c
>> +++ b/arch/riscv/kernel/process.c
>> @@ -203,6 +203,10 @@ int copy_thread(struct task_struct *p, const struct
>> kernel_clone_args *args)
>>       unsigned long tls = args->tls;
>>       struct pt_regs *childregs = task_pt_regs(p);
>>   +    /* Ensure all threads in this mm have the same pointer masking mode. */
>> +    if (IS_ENABLED(CONFIG_RISCV_ISA_SUPM) && p->mm && (clone_flags & CLONE_VM))
>> +        set_bit(MM_CONTEXT_LOCK_PMLEN, &p->mm->context.flags);
>> +
>>       memset(&p->thread.s, 0, sizeof(p->thread.s));
>>         /* p->thread holds context to be restored by __switch_to() */
>> @@ -248,10 +252,16 @@ enum {
>>   static bool have_user_pmlen_7;
>>   static bool have_user_pmlen_16;
>>   +/*
>> + * Control the relaxed ABI allowing tagged user addresses into the kernel.
>> + */
>> +static unsigned int tagged_addr_disabled;
>> +
>>   long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg)
>>   {
>> -    unsigned long valid_mask = PR_PMLEN_MASK;
>> +    unsigned long valid_mask = PR_PMLEN_MASK | PR_TAGGED_ADDR_ENABLE;
>>       struct thread_info *ti = task_thread_info(task);
>> +    struct mm_struct *mm = task->mm;
>>       unsigned long pmm;
>>       u8 pmlen;
>>   @@ -266,16 +276,41 @@ long set_tagged_addr_ctrl(struct task_struct *task,
>> unsigned long arg)
>>        * in case choosing a larger PMLEN has a performance impact.
>>        */
>>       pmlen = FIELD_GET(PR_PMLEN_MASK, arg);
>> -    if (pmlen == PMLEN_0)
>> +    if (pmlen == PMLEN_0) {
>>           pmm = ENVCFG_PMM_PMLEN_0;
>> -    else if (pmlen <= PMLEN_7 && have_user_pmlen_7)
>> +    } else if (pmlen <= PMLEN_7 && have_user_pmlen_7) {
>> +        pmlen = PMLEN_7;
>>           pmm = ENVCFG_PMM_PMLEN_7;
>> -    else if (pmlen <= PMLEN_16 && have_user_pmlen_16)
>> +    } else if (pmlen <= PMLEN_16 && have_user_pmlen_16) {
>> +        pmlen = PMLEN_16;
>>           pmm = ENVCFG_PMM_PMLEN_16;
>> -    else
>> +    } else {
>>           return -EINVAL;
>> +    }
>> +
>> +    /*
>> +     * Do not allow the enabling of the tagged address ABI if globally
>> +     * disabled via sysctl abi.tagged_addr_disabled, if pointer masking
>> +     * is disabled for userspace.
>> +     */
>> +    if (arg & PR_TAGGED_ADDR_ENABLE && (tagged_addr_disabled || !pmlen))
>> +        return -EINVAL;
>> +
>> +    if (!(arg & PR_TAGGED_ADDR_ENABLE))
>> +        pmlen = PMLEN_0;
>> +
>> +    if (mmap_write_lock_killable(mm))
>> +        return -EINTR;
>> +
>> +    if (test_bit(MM_CONTEXT_LOCK_PMLEN, &mm->context.flags) &&
>> mm->context.pmlen != pmlen) {
>> +        mmap_write_unlock(mm);
>> +        return -EBUSY;
>> +    }
>>         envcfg_update_bits(task, ENVCFG_PMM, pmm);
>> +    mm->context.pmlen = pmlen;
>> +
>> +    mmap_write_unlock(mm);
>>         return 0;
>>   }
>> @@ -288,6 +323,10 @@ long get_tagged_addr_ctrl(struct task_struct *task)
>>       if (is_compat_thread(ti))
>>           return -EINVAL;
>>   +    /*
>> +     * The mm context's pmlen is set only when the tagged address ABI is
>> +     * enabled, so the effective PMLEN must be extracted from envcfg.PMM.
>> +     */
>>       switch (task->thread.envcfg & ENVCFG_PMM) {
>>       case ENVCFG_PMM_PMLEN_7:
>>           ret = FIELD_PREP(PR_PMLEN_MASK, PMLEN_7);
>> @@ -297,6 +336,9 @@ long get_tagged_addr_ctrl(struct task_struct *task)
>>           break;
>>       }
>>   +    if (task->mm->context.pmlen)
>> +        ret |= PR_TAGGED_ADDR_ENABLE;
>> +
>>       return ret;
>>   }
>>   @@ -306,6 +348,24 @@ static bool try_to_set_pmm(unsigned long value)
>>       return (csr_read_clear(CSR_ENVCFG, ENVCFG_PMM) & ENVCFG_PMM) == value;
>>   }
>>   +/*
>> + * Global sysctl to disable the tagged user addresses support. This control
>> + * only prevents the tagged address ABI enabling via prctl() and does not
>> + * disable it for tasks that already opted in to the relaxed ABI.
>> + */
>> +
>> +static struct ctl_table tagged_addr_sysctl_table[] = {
>> +    {
>> +        .procname    = "tagged_addr_disabled",
>> +        .mode        = 0644,
>> +        .data        = &tagged_addr_disabled,
>> +        .maxlen        = sizeof(int),
>> +        .proc_handler    = proc_dointvec_minmax,
>> +        .extra1        = SYSCTL_ZERO,
>> +        .extra2        = SYSCTL_ONE,
>> +    },
>> +};
>> +
>>   static int __init tagged_addr_init(void)
>>   {
>>       if (!riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM))
>> @@ -319,6 +379,9 @@ static int __init tagged_addr_init(void)
>>       have_user_pmlen_7 = try_to_set_pmm(ENVCFG_PMM_PMLEN_7);
>>       have_user_pmlen_16 = try_to_set_pmm(ENVCFG_PMM_PMLEN_16);
>>   +    if (!register_sysctl("abi", tagged_addr_sysctl_table))
>> +        return -EINVAL;
>> +
>>       return 0;
>>   }
>>   core_initcall(tagged_addr_init);

Re: [PATCH v3 05/10] riscv: Add support for the tagged address ABI

[Alexandre Ghiti]

On 14/08/2024 18:14, Samuel Holland wrote:
> Hi Alex,
>
> On 2024-08-14 10:10 AM, Alexandre Ghiti wrote:
>> On 14/08/2024 10:13, Samuel Holland wrote:
>>> When pointer masking is enabled for userspace, the kernel can accept
>>> tagged pointers as arguments to some system calls. Allow this by
>>> untagging the pointers in access_ok() and the uaccess routines. The
>>> uaccess routines must peform untagging in software because U-mode and
>>> S-mode have entirely separate pointer masking configurations. In fact,
>>> hardware may not even implement pointer masking for S-mode.
>>>
>>> Since the number of tag bits is variable, untagged_addr_remote() needs
>>> to know what PMLEN to use for the remote mm. Therefore, the pointer
>>> masking mode must be the same for all threads sharing an mm. Enforce
>>> this with a lock flag in the mm context, as x86 does for LAM. The flag
>>> gets reset in init_new_context() during fork(), as the new mm is no
>>> longer multithreaded.
>>>
>>> Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
>>> ---
>>>
>>> Changes in v3:
>>>    - Use IS_ENABLED instead of #ifdef when possible
>>>    - Implement mm_untag_mask()
>>>    - Remove pmlen from struct thread_info (now only in mm_context_t)
>>>
>>> Changes in v2:
>>>    - Implement untagged_addr_remote()
>>>    - Restrict PMLEN changes once a process is multithreaded
>>>
>>>    arch/riscv/include/asm/mmu.h         |  7 +++
>>>    arch/riscv/include/asm/mmu_context.h | 13 +++++
>>>    arch/riscv/include/asm/uaccess.h     | 58 ++++++++++++++++++++--
>>>    arch/riscv/kernel/process.c          | 73 ++++++++++++++++++++++++++--
>>>    4 files changed, 141 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/arch/riscv/include/asm/mmu.h b/arch/riscv/include/asm/mmu.h
>>> index c9e03e9da3dc..1cc90465d75b 100644
>>> --- a/arch/riscv/include/asm/mmu.h
>>> +++ b/arch/riscv/include/asm/mmu.h
>>> @@ -25,9 +25,16 @@ typedef struct {
>>>    #ifdef CONFIG_BINFMT_ELF_FDPIC
>>>        unsigned long exec_fdpic_loadmap;
>>>        unsigned long interp_fdpic_loadmap;
>>> +#endif
>>> +    unsigned long flags;
>>> +#ifdef CONFIG_RISCV_ISA_SUPM
>>> +    u8 pmlen;
>>>    #endif
>>>    } mm_context_t;
>>>    +/* Lock the pointer masking mode because this mm is multithreaded */
>>> +#define MM_CONTEXT_LOCK_PMLEN    0
>>> +
>>>    #define cntx2asid(cntx)        ((cntx) & SATP_ASID_MASK)
>>>    #define cntx2version(cntx)    ((cntx) & ~SATP_ASID_MASK)
>>>    diff --git a/arch/riscv/include/asm/mmu_context.h
>>> b/arch/riscv/include/asm/mmu_context.h
>>> index 7030837adc1a..8c4bc49a3a0f 100644
>>> --- a/arch/riscv/include/asm/mmu_context.h
>>> +++ b/arch/riscv/include/asm/mmu_context.h
>>> @@ -20,6 +20,9 @@ void switch_mm(struct mm_struct *prev, struct mm_struct *next,
>>>    static inline void activate_mm(struct mm_struct *prev,
>>>                       struct mm_struct *next)
>>>    {
>>> +#ifdef CONFIG_RISCV_ISA_SUPM
>>> +    next->context.pmlen = 0;
>>> +#endif
>>>        switch_mm(prev, next, NULL);
>>>    }
>>>    @@ -30,11 +33,21 @@ static inline int init_new_context(struct task_struct *tsk,
>>>    #ifdef CONFIG_MMU
>>>        atomic_long_set(&mm->context.id, 0);
>>>    #endif
>>> +    if (IS_ENABLED(CONFIG_RISCV_ISA_SUPM))
>>> +        clear_bit(MM_CONTEXT_LOCK_PMLEN, &mm->context.flags);
>>>        return 0;
>>>    }
>>>      DECLARE_STATIC_KEY_FALSE(use_asid_allocator);
>>>    +#ifdef CONFIG_RISCV_ISA_SUPM
>>> +#define mm_untag_mask mm_untag_mask
>>> +static inline unsigned long mm_untag_mask(struct mm_struct *mm)
>>> +{
>>> +    return -1UL >> mm->context.pmlen;
>>> +}
>>> +#endif
>>> +
>>>    #include <asm-generic/mmu_context.h>
>>>      #endif /* _ASM_RISCV_MMU_CONTEXT_H */
>>> diff --git a/arch/riscv/include/asm/uaccess.h b/arch/riscv/include/asm/uaccess.h
>>> index 72ec1d9bd3f3..6416559232a2 100644
>>> --- a/arch/riscv/include/asm/uaccess.h
>>> +++ b/arch/riscv/include/asm/uaccess.h
>>> @@ -9,8 +9,56 @@
>>>    #define _ASM_RISCV_UACCESS_H
>>>      #include <asm/asm-extable.h>
>>> +#include <asm/cpufeature.h>
>>>    #include <asm/pgtable.h>        /* for TASK_SIZE */
>>>    +#ifdef CONFIG_RISCV_ISA_SUPM
>>> +static inline unsigned long __untagged_addr(unsigned long addr)
>>> +{
>>> +    if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM)) {
>>> +        u8 pmlen = current->mm->context.pmlen;
>>> +
>>> +        /* Virtual addresses are sign-extended; physical addresses are
>>> zero-extended. */
>>> +        if (IS_ENABLED(CONFIG_MMU))
>>> +            return (long)(addr << pmlen) >> pmlen;
>>> +        else
>>> +            return (addr << pmlen) >> pmlen;
>>> +    }
>>> +
>>> +    return addr;
>>> +}
>>> +
>>> +#define untagged_addr(addr) ({                        \
>>> +    unsigned long __addr = (__force unsigned long)(addr);        \
>>> +    (__force __typeof__(addr))__untagged_addr(__addr);        \
>>> +})
>>> +
>>> +static inline unsigned long __untagged_addr_remote(struct mm_struct *mm,
>>> unsigned long addr)
>>> +{
>>> +    if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM)) {
>>> +        u8 pmlen = mm->context.pmlen;
>>> +
>>> +        /* Virtual addresses are sign-extended; physical addresses are
>>> zero-extended. */
>>> +        if (IS_ENABLED(CONFIG_MMU))
>>> +            return (long)(addr << pmlen) >> pmlen;
>>> +        else
>>> +            return (addr << pmlen) >> pmlen;
>>> +    }
>>> +
>>> +    return addr;
>>> +}
>>
>> I should have mentioned that in v2: now that you removed the thread_info pmlen
>> field, __untagged_addr_remote() and __untagged_addr() are almost the same, can
>> you merge them?
> I can merge them, but this places the load of current->mm outside the static
> branch. If you think that is okay, then I'll merge them for v4.


I think it's ok, it's not a big overhead :)

Thanks,

Alex


> Regards,
> Samuel
>
>>> +
>>> +#define untagged_addr_remote(mm, addr) ({                \
>>> +    unsigned long __addr = (__force unsigned long)(addr);        \
>>> +    mmap_assert_locked(mm);                        \
>>> +    (__force __typeof__(addr))__untagged_addr_remote(mm, __addr);    \
>>> +})
>>> +
>>> +#define access_ok(addr, size) likely(__access_ok(untagged_addr(addr), size))
>>> +#else
>>> +#define untagged_addr(addr) (addr)
>>> +#endif
>>> +
>>>    /*
>>>     * User space memory access functions
>>>     */
>>> @@ -130,7 +178,7 @@ do {                                \
>>>     */
>>>    #define __get_user(x, ptr)                    \
>>>    ({                                \
>>> -    const __typeof__(*(ptr)) __user *__gu_ptr = (ptr);    \
>>> +    const __typeof__(*(ptr)) __user *__gu_ptr = untagged_addr(ptr); \
>>>        long __gu_err = 0;                    \
>>>                                    \
>>>        __chk_user_ptr(__gu_ptr);                \
>>> @@ -246,7 +294,7 @@ do {                                \
>>>     */
>>>    #define __put_user(x, ptr)                    \
>>>    ({                                \
>>> -    __typeof__(*(ptr)) __user *__gu_ptr = (ptr);        \
>>> +    __typeof__(*(ptr)) __user *__gu_ptr = untagged_addr(ptr); \
>>>        __typeof__(*__gu_ptr) __val = (x);            \
>>>        long __pu_err = 0;                    \
>>>                                    \
>>> @@ -293,13 +341,13 @@ unsigned long __must_check __asm_copy_from_user(void *to,
>>>    static inline unsigned long
>>>    raw_copy_from_user(void *to, const void __user *from, unsigned long n)
>>>    {
>>> -    return __asm_copy_from_user(to, from, n);
>>> +    return __asm_copy_from_user(to, untagged_addr(from), n);
>>>    }
>>>      static inline unsigned long
>>>    raw_copy_to_user(void __user *to, const void *from, unsigned long n)
>>>    {
>>> -    return __asm_copy_to_user(to, from, n);
>>> +    return __asm_copy_to_user(untagged_addr(to), from, n);
>>>    }
>>>      extern long strncpy_from_user(char *dest, const char __user *src, long
>>> count);
>>> @@ -314,7 +362,7 @@ unsigned long __must_check clear_user(void __user *to,
>>> unsigned long n)
>>>    {
>>>        might_fault();
>>>        return access_ok(to, n) ?
>>> -        __clear_user(to, n) : n;
>>> +        __clear_user(untagged_addr(to), n) : n;
>>>    }
>>>      #define __get_kernel_nofault(dst, src, type, err_label)            \
>>> diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
>>> index 1280a7c4a412..f4d8e5c3bb84 100644
>>> --- a/arch/riscv/kernel/process.c
>>> +++ b/arch/riscv/kernel/process.c
>>> @@ -203,6 +203,10 @@ int copy_thread(struct task_struct *p, const struct
>>> kernel_clone_args *args)
>>>        unsigned long tls = args->tls;
>>>        struct pt_regs *childregs = task_pt_regs(p);
>>>    +    /* Ensure all threads in this mm have the same pointer masking mode. */
>>> +    if (IS_ENABLED(CONFIG_RISCV_ISA_SUPM) && p->mm && (clone_flags & CLONE_VM))
>>> +        set_bit(MM_CONTEXT_LOCK_PMLEN, &p->mm->context.flags);
>>> +
>>>        memset(&p->thread.s, 0, sizeof(p->thread.s));
>>>          /* p->thread holds context to be restored by __switch_to() */
>>> @@ -248,10 +252,16 @@ enum {
>>>    static bool have_user_pmlen_7;
>>>    static bool have_user_pmlen_16;
>>>    +/*
>>> + * Control the relaxed ABI allowing tagged user addresses into the kernel.
>>> + */
>>> +static unsigned int tagged_addr_disabled;
>>> +
>>>    long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg)
>>>    {
>>> -    unsigned long valid_mask = PR_PMLEN_MASK;
>>> +    unsigned long valid_mask = PR_PMLEN_MASK | PR_TAGGED_ADDR_ENABLE;
>>>        struct thread_info *ti = task_thread_info(task);
>>> +    struct mm_struct *mm = task->mm;
>>>        unsigned long pmm;
>>>        u8 pmlen;
>>>    @@ -266,16 +276,41 @@ long set_tagged_addr_ctrl(struct task_struct *task,
>>> unsigned long arg)
>>>         * in case choosing a larger PMLEN has a performance impact.
>>>         */
>>>        pmlen = FIELD_GET(PR_PMLEN_MASK, arg);
>>> -    if (pmlen == PMLEN_0)
>>> +    if (pmlen == PMLEN_0) {
>>>            pmm = ENVCFG_PMM_PMLEN_0;
>>> -    else if (pmlen <= PMLEN_7 && have_user_pmlen_7)
>>> +    } else if (pmlen <= PMLEN_7 && have_user_pmlen_7) {
>>> +        pmlen = PMLEN_7;
>>>            pmm = ENVCFG_PMM_PMLEN_7;
>>> -    else if (pmlen <= PMLEN_16 && have_user_pmlen_16)
>>> +    } else if (pmlen <= PMLEN_16 && have_user_pmlen_16) {
>>> +        pmlen = PMLEN_16;
>>>            pmm = ENVCFG_PMM_PMLEN_16;
>>> -    else
>>> +    } else {
>>>            return -EINVAL;
>>> +    }
>>> +
>>> +    /*
>>> +     * Do not allow the enabling of the tagged address ABI if globally
>>> +     * disabled via sysctl abi.tagged_addr_disabled, if pointer masking
>>> +     * is disabled for userspace.
>>> +     */
>>> +    if (arg & PR_TAGGED_ADDR_ENABLE && (tagged_addr_disabled || !pmlen))
>>> +        return -EINVAL;
>>> +
>>> +    if (!(arg & PR_TAGGED_ADDR_ENABLE))
>>> +        pmlen = PMLEN_0;
>>> +
>>> +    if (mmap_write_lock_killable(mm))
>>> +        return -EINTR;
>>> +
>>> +    if (test_bit(MM_CONTEXT_LOCK_PMLEN, &mm->context.flags) &&
>>> mm->context.pmlen != pmlen) {
>>> +        mmap_write_unlock(mm);
>>> +        return -EBUSY;
>>> +    }
>>>          envcfg_update_bits(task, ENVCFG_PMM, pmm);
>>> +    mm->context.pmlen = pmlen;
>>> +
>>> +    mmap_write_unlock(mm);
>>>          return 0;
>>>    }
>>> @@ -288,6 +323,10 @@ long get_tagged_addr_ctrl(struct task_struct *task)
>>>        if (is_compat_thread(ti))
>>>            return -EINVAL;
>>>    +    /*
>>> +     * The mm context's pmlen is set only when the tagged address ABI is
>>> +     * enabled, so the effective PMLEN must be extracted from envcfg.PMM.
>>> +     */
>>>        switch (task->thread.envcfg & ENVCFG_PMM) {
>>>        case ENVCFG_PMM_PMLEN_7:
>>>            ret = FIELD_PREP(PR_PMLEN_MASK, PMLEN_7);
>>> @@ -297,6 +336,9 @@ long get_tagged_addr_ctrl(struct task_struct *task)
>>>            break;
>>>        }
>>>    +    if (task->mm->context.pmlen)
>>> +        ret |= PR_TAGGED_ADDR_ENABLE;
>>> +
>>>        return ret;
>>>    }
>>>    @@ -306,6 +348,24 @@ static bool try_to_set_pmm(unsigned long value)
>>>        return (csr_read_clear(CSR_ENVCFG, ENVCFG_PMM) & ENVCFG_PMM) == value;
>>>    }
>>>    +/*
>>> + * Global sysctl to disable the tagged user addresses support. This control
>>> + * only prevents the tagged address ABI enabling via prctl() and does not
>>> + * disable it for tasks that already opted in to the relaxed ABI.
>>> + */
>>> +
>>> +static struct ctl_table tagged_addr_sysctl_table[] = {
>>> +    {
>>> +        .procname    = "tagged_addr_disabled",
>>> +        .mode        = 0644,
>>> +        .data        = &tagged_addr_disabled,
>>> +        .maxlen        = sizeof(int),
>>> +        .proc_handler    = proc_dointvec_minmax,
>>> +        .extra1        = SYSCTL_ZERO,
>>> +        .extra2        = SYSCTL_ONE,
>>> +    },
>>> +};
>>> +
>>>    static int __init tagged_addr_init(void)
>>>    {
>>>        if (!riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM))
>>> @@ -319,6 +379,9 @@ static int __init tagged_addr_init(void)
>>>        have_user_pmlen_7 = try_to_set_pmm(ENVCFG_PMM_PMLEN_7);
>>>        have_user_pmlen_16 = try_to_set_pmm(ENVCFG_PMM_PMLEN_16);
>>>    +    if (!register_sysctl("abi", tagged_addr_sysctl_table))
>>> +        return -EINVAL;
>>> +
>>>        return 0;
>>>    }
>>>    core_initcall(tagged_addr_init);
>
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

Re: [PATCH v3 04/10] riscv: Add support for userspace pointer masking

[Anup Patel]

On Wed, Aug 14, 2024 at 1:45 PM Samuel Holland
<samuel.holland@sifive.com> wrote:
>
> RISC-V supports pointer masking with a variable number of tag bits
> (which is called "PMLEN" in the specification) and which is configured
> at the next higher privilege level.
>
> Wire up the PR_SET_TAGGED_ADDR_CTRL and PR_GET_TAGGED_ADDR_CTRL prctls
> so userspace can request a lower bound on the number of tag bits and
> determine the actual number of tag bits. As with arm64's
> PR_TAGGED_ADDR_ENABLE, the pointer masking configuration is
> thread-scoped, inherited on clone() and fork() and cleared on execve().
>
> Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
> ---
>
> Changes in v3:
>  - Rename CONFIG_RISCV_ISA_POINTER_MASKING to CONFIG_RISCV_ISA_SUPM,
>    since it only controls the userspace part of pointer masking
>  - Use IS_ENABLED instead of #ifdef when possible
>  - Use an enum for the supported PMLEN values
>  - Simplify the logic in set_tagged_addr_ctrl()
>
> Changes in v2:
>  - Rebase on riscv/linux.git for-next
>  - Add and use the envcfg_update_bits() helper function
>  - Inline flush_tagged_addr_state()
>
>  arch/riscv/Kconfig                 | 11 ++++
>  arch/riscv/include/asm/processor.h |  8 +++
>  arch/riscv/include/asm/switch_to.h | 11 ++++
>  arch/riscv/kernel/process.c        | 90 ++++++++++++++++++++++++++++++
>  include/uapi/linux/prctl.h         |  3 +
>  5 files changed, 123 insertions(+)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 0f3cd7c3a436..817437157138 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -512,6 +512,17 @@ config RISCV_ISA_C
>
>           If you don't know what to do here, say Y.
>
> +config RISCV_ISA_SUPM
> +       bool "Supm extension for userspace pointer masking"
> +       depends on 64BIT
> +       default y
> +       help
> +         Add support for pointer masking in userspace (Supm) when the
> +         underlying hardware extension (Smnpm or Ssnpm) is detected at boot.
> +
> +         If this option is disabled, userspace will be unable to use
> +         the prctl(PR_{SET,GET}_TAGGED_ADDR_CTRL) API.
> +
>  config RISCV_ISA_SVNAPOT
>         bool "Svnapot extension support for supervisor mode NAPOT pages"
>         depends on 64BIT && MMU
> diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
> index 586e4ab701c4..5c4d4fb97314 100644
> --- a/arch/riscv/include/asm/processor.h
> +++ b/arch/riscv/include/asm/processor.h
> @@ -200,6 +200,14 @@ extern int set_unalign_ctl(struct task_struct *tsk, unsigned int val);
>  #define RISCV_SET_ICACHE_FLUSH_CTX(arg1, arg2) riscv_set_icache_flush_ctx(arg1, arg2)
>  extern int riscv_set_icache_flush_ctx(unsigned long ctx, unsigned long per_thread);
>
> +#ifdef CONFIG_RISCV_ISA_SUPM
> +/* PR_{SET,GET}_TAGGED_ADDR_CTRL prctl */
> +long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg);
> +long get_tagged_addr_ctrl(struct task_struct *task);
> +#define SET_TAGGED_ADDR_CTRL(arg)      set_tagged_addr_ctrl(current, arg)
> +#define GET_TAGGED_ADDR_CTRL()         get_tagged_addr_ctrl(current)
> +#endif
> +
>  #endif /* __ASSEMBLY__ */
>
>  #endif /* _ASM_RISCV_PROCESSOR_H */
> diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/switch_to.h
> index 9685cd85e57c..94e33216b2d9 100644
> --- a/arch/riscv/include/asm/switch_to.h
> +++ b/arch/riscv/include/asm/switch_to.h
> @@ -70,6 +70,17 @@ static __always_inline bool has_fpu(void) { return false; }
>  #define __switch_to_fpu(__prev, __next) do { } while (0)
>  #endif
>
> +static inline void envcfg_update_bits(struct task_struct *task,
> +                                     unsigned long mask, unsigned long val)
> +{
> +       unsigned long envcfg;
> +
> +       envcfg = (task->thread.envcfg & ~mask) | val;
> +       task->thread.envcfg = envcfg;
> +       if (task == current)
> +               csr_write(CSR_ENVCFG, envcfg);
> +}
> +
>  static inline void __switch_to_envcfg(struct task_struct *next)
>  {
>         asm volatile (ALTERNATIVE("nop", "csrw " __stringify(CSR_ENVCFG) ", %0",
> diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
> index e4bc61c4e58a..1280a7c4a412 100644
> --- a/arch/riscv/kernel/process.c
> +++ b/arch/riscv/kernel/process.c
> @@ -7,6 +7,7 @@
>   * Copyright (C) 2017 SiFive
>   */
>
> +#include <linux/bitfield.h>
>  #include <linux/cpu.h>
>  #include <linux/kernel.h>
>  #include <linux/sched.h>
> @@ -171,6 +172,9 @@ void flush_thread(void)
>         memset(&current->thread.vstate, 0, sizeof(struct __riscv_v_ext_state));
>         clear_tsk_thread_flag(current, TIF_RISCV_V_DEFER_RESTORE);
>  #endif
> +       if (IS_ENABLED(CONFIG_RISCV_ISA_SUPM) &&
> +           riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM))
> +               envcfg_update_bits(current, ENVCFG_PMM, ENVCFG_PMM_PMLEN_0);

Seeing a compile warning with this patch on RV32.

linux/arch/riscv/kernel/process.c: In function 'flush_thread':
linux/arch/riscv/include/asm/csr.h:202:41: warning: conversion from
'long long unsigned int' to 'long unsigned int' changes value from
'12884901888' to '0' [-Woverflow]
  202 | #define ENVCFG_PMM                      (_AC(0x3, ULL) << 32)
      |                                         ^~~~~~~~~~~~~~~~~~~~~
linux/arch/riscv/kernel/process.c:179:45: note: in expansion of macro
'ENVCFG_PMM'
  179 |                 envcfg_update_bits(current, ENVCFG_PMM,
ENVCFG_PMM_PMLEN_0);
      |                                             ^~~~~~~~~~

Regards,
Anup

>  }
>
>  void arch_release_task_struct(struct task_struct *tsk)
> @@ -233,3 +237,89 @@ void __init arch_task_cache_init(void)
>  {
>         riscv_v_setup_ctx_cache();
>  }
> +
> +#ifdef CONFIG_RISCV_ISA_SUPM
> +enum {
> +       PMLEN_0 = 0,
> +       PMLEN_7 = 7,
> +       PMLEN_16 = 16,
> +};
> +
> +static bool have_user_pmlen_7;
> +static bool have_user_pmlen_16;
> +
> +long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg)
> +{
> +       unsigned long valid_mask = PR_PMLEN_MASK;
> +       struct thread_info *ti = task_thread_info(task);
> +       unsigned long pmm;
> +       u8 pmlen;
> +
> +       if (is_compat_thread(ti))
> +               return -EINVAL;
> +
> +       if (arg & ~valid_mask)
> +               return -EINVAL;
> +
> +       /*
> +        * Prefer the smallest PMLEN that satisfies the user's request,
> +        * in case choosing a larger PMLEN has a performance impact.
> +        */
> +       pmlen = FIELD_GET(PR_PMLEN_MASK, arg);
> +       if (pmlen == PMLEN_0)
> +               pmm = ENVCFG_PMM_PMLEN_0;
> +       else if (pmlen <= PMLEN_7 && have_user_pmlen_7)
> +               pmm = ENVCFG_PMM_PMLEN_7;
> +       else if (pmlen <= PMLEN_16 && have_user_pmlen_16)
> +               pmm = ENVCFG_PMM_PMLEN_16;
> +       else
> +               return -EINVAL;
> +
> +       envcfg_update_bits(task, ENVCFG_PMM, pmm);
> +
> +       return 0;
> +}
> +
> +long get_tagged_addr_ctrl(struct task_struct *task)
> +{
> +       struct thread_info *ti = task_thread_info(task);
> +       long ret = 0;
> +
> +       if (is_compat_thread(ti))
> +               return -EINVAL;
> +
> +       switch (task->thread.envcfg & ENVCFG_PMM) {
> +       case ENVCFG_PMM_PMLEN_7:
> +               ret = FIELD_PREP(PR_PMLEN_MASK, PMLEN_7);
> +               break;
> +       case ENVCFG_PMM_PMLEN_16:
> +               ret = FIELD_PREP(PR_PMLEN_MASK, PMLEN_16);
> +               break;
> +       }
> +
> +       return ret;
> +}
> +
> +static bool try_to_set_pmm(unsigned long value)
> +{
> +       csr_set(CSR_ENVCFG, value);
> +       return (csr_read_clear(CSR_ENVCFG, ENVCFG_PMM) & ENVCFG_PMM) == value;
> +}
> +
> +static int __init tagged_addr_init(void)
> +{
> +       if (!riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM))
> +               return 0;
> +
> +       /*
> +        * envcfg.PMM is a WARL field. Detect which values are supported.
> +        * Assume the supported PMLEN values are the same on all harts.
> +        */
> +       csr_clear(CSR_ENVCFG, ENVCFG_PMM);
> +       have_user_pmlen_7 = try_to_set_pmm(ENVCFG_PMM_PMLEN_7);
> +       have_user_pmlen_16 = try_to_set_pmm(ENVCFG_PMM_PMLEN_16);
> +
> +       return 0;
> +}
> +core_initcall(tagged_addr_init);
> +#endif /* CONFIG_RISCV_ISA_SUPM */
> diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
> index 35791791a879..6e84c827869b 100644
> --- a/include/uapi/linux/prctl.h
> +++ b/include/uapi/linux/prctl.h
> @@ -244,6 +244,9 @@ struct prctl_mm_map {
>  # define PR_MTE_TAG_MASK               (0xffffUL << PR_MTE_TAG_SHIFT)
>  /* Unused; kept only for source compatibility */
>  # define PR_MTE_TCF_SHIFT              1
> +/* RISC-V pointer masking tag length */
> +# define PR_PMLEN_SHIFT                        24
> +# define PR_PMLEN_MASK                 (0x7fUL << PR_PMLEN_SHIFT)
>
>  /* Control reclaim behavior when allocating memory */
>  #define PR_SET_IO_FLUSHER              57
> --
> 2.45.1
>
>
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

Re: [PATCH v3 04/10] riscv: Add support for userspace pointer masking

[Samuel Holland]

Hi Anup,

On 2024-08-16 8:21 AM, Anup Patel wrote:
> On Wed, Aug 14, 2024 at 1:45 PM Samuel Holland
> <samuel.holland@sifive.com> wrote:
>>
>> RISC-V supports pointer masking with a variable number of tag bits
>> (which is called "PMLEN" in the specification) and which is configured
>> at the next higher privilege level.
>>
>> Wire up the PR_SET_TAGGED_ADDR_CTRL and PR_GET_TAGGED_ADDR_CTRL prctls
>> so userspace can request a lower bound on the number of tag bits and
>> determine the actual number of tag bits. As with arm64's
>> PR_TAGGED_ADDR_ENABLE, the pointer masking configuration is
>> thread-scoped, inherited on clone() and fork() and cleared on execve().
>>
>> Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
>> ---
>>
>> Changes in v3:
>>  - Rename CONFIG_RISCV_ISA_POINTER_MASKING to CONFIG_RISCV_ISA_SUPM,
>>    since it only controls the userspace part of pointer masking
>>  - Use IS_ENABLED instead of #ifdef when possible
>>  - Use an enum for the supported PMLEN values
>>  - Simplify the logic in set_tagged_addr_ctrl()
>>
>> Changes in v2:
>>  - Rebase on riscv/linux.git for-next
>>  - Add and use the envcfg_update_bits() helper function
>>  - Inline flush_tagged_addr_state()
>>
>>  arch/riscv/Kconfig                 | 11 ++++
>>  arch/riscv/include/asm/processor.h |  8 +++
>>  arch/riscv/include/asm/switch_to.h | 11 ++++
>>  arch/riscv/kernel/process.c        | 90 ++++++++++++++++++++++++++++++
>>  include/uapi/linux/prctl.h         |  3 +
>>  5 files changed, 123 insertions(+)
>>
>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>> index 0f3cd7c3a436..817437157138 100644
>> --- a/arch/riscv/Kconfig
>> +++ b/arch/riscv/Kconfig
>> @@ -512,6 +512,17 @@ config RISCV_ISA_C
>>
>>           If you don't know what to do here, say Y.
>>
>> +config RISCV_ISA_SUPM
>> +       bool "Supm extension for userspace pointer masking"
>> +       depends on 64BIT
>> +       default y
>> +       help
>> +         Add support for pointer masking in userspace (Supm) when the
>> +         underlying hardware extension (Smnpm or Ssnpm) is detected at boot.
>> +
>> +         If this option is disabled, userspace will be unable to use
>> +         the prctl(PR_{SET,GET}_TAGGED_ADDR_CTRL) API.
>> +
>>  config RISCV_ISA_SVNAPOT
>>         bool "Svnapot extension support for supervisor mode NAPOT pages"
>>         depends on 64BIT && MMU
>> diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
>> index 586e4ab701c4..5c4d4fb97314 100644
>> --- a/arch/riscv/include/asm/processor.h
>> +++ b/arch/riscv/include/asm/processor.h
>> @@ -200,6 +200,14 @@ extern int set_unalign_ctl(struct task_struct *tsk, unsigned int val);
>>  #define RISCV_SET_ICACHE_FLUSH_CTX(arg1, arg2) riscv_set_icache_flush_ctx(arg1, arg2)
>>  extern int riscv_set_icache_flush_ctx(unsigned long ctx, unsigned long per_thread);
>>
>> +#ifdef CONFIG_RISCV_ISA_SUPM
>> +/* PR_{SET,GET}_TAGGED_ADDR_CTRL prctl */
>> +long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg);
>> +long get_tagged_addr_ctrl(struct task_struct *task);
>> +#define SET_TAGGED_ADDR_CTRL(arg)      set_tagged_addr_ctrl(current, arg)
>> +#define GET_TAGGED_ADDR_CTRL()         get_tagged_addr_ctrl(current)
>> +#endif
>> +
>>  #endif /* __ASSEMBLY__ */
>>
>>  #endif /* _ASM_RISCV_PROCESSOR_H */
>> diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/switch_to.h
>> index 9685cd85e57c..94e33216b2d9 100644
>> --- a/arch/riscv/include/asm/switch_to.h
>> +++ b/arch/riscv/include/asm/switch_to.h
>> @@ -70,6 +70,17 @@ static __always_inline bool has_fpu(void) { return false; }
>>  #define __switch_to_fpu(__prev, __next) do { } while (0)
>>  #endif
>>
>> +static inline void envcfg_update_bits(struct task_struct *task,
>> +                                     unsigned long mask, unsigned long val)
>> +{
>> +       unsigned long envcfg;
>> +
>> +       envcfg = (task->thread.envcfg & ~mask) | val;
>> +       task->thread.envcfg = envcfg;
>> +       if (task == current)
>> +               csr_write(CSR_ENVCFG, envcfg);
>> +}
>> +
>>  static inline void __switch_to_envcfg(struct task_struct *next)
>>  {
>>         asm volatile (ALTERNATIVE("nop", "csrw " __stringify(CSR_ENVCFG) ", %0",
>> diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
>> index e4bc61c4e58a..1280a7c4a412 100644
>> --- a/arch/riscv/kernel/process.c
>> +++ b/arch/riscv/kernel/process.c
>> @@ -7,6 +7,7 @@
>>   * Copyright (C) 2017 SiFive
>>   */
>>
>> +#include <linux/bitfield.h>
>>  #include <linux/cpu.h>
>>  #include <linux/kernel.h>
>>  #include <linux/sched.h>
>> @@ -171,6 +172,9 @@ void flush_thread(void)
>>         memset(&current->thread.vstate, 0, sizeof(struct __riscv_v_ext_state));
>>         clear_tsk_thread_flag(current, TIF_RISCV_V_DEFER_RESTORE);
>>  #endif
>> +       if (IS_ENABLED(CONFIG_RISCV_ISA_SUPM) &&
>> +           riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM))
>> +               envcfg_update_bits(current, ENVCFG_PMM, ENVCFG_PMM_PMLEN_0);
> 
> Seeing a compile warning with this patch on RV32.
> 
> linux/arch/riscv/kernel/process.c: In function 'flush_thread':
> linux/arch/riscv/include/asm/csr.h:202:41: warning: conversion from
> 'long long unsigned int' to 'long unsigned int' changes value from
> '12884901888' to '0' [-Woverflow]
>   202 | #define ENVCFG_PMM                      (_AC(0x3, ULL) << 32)
>       |                                         ^~~~~~~~~~~~~~~~~~~~~
> linux/arch/riscv/kernel/process.c:179:45: note: in expansion of macro
> 'ENVCFG_PMM'
>   179 |                 envcfg_update_bits(current, ENVCFG_PMM,
> ENVCFG_PMM_PMLEN_0);
>       |                                             ^~~~~~~~~~

Right, thanks, that's why I needed to use #ifdef here before. I'll switch this
instance back for v4.

Regards,
Samuel