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* [PATCH v3 0/4] openrisc: Add support for KProbes and Kretprobes
       [not found] <20260930202744.50489-1-sahilcdq0@gmail.com>
@ 2026-10-26 20:12 ` Sahil Siddiq
  2026-10-26 20:12 ` [PATCH v3 1/4] openrisc: Add utilities and clean up simulation of instructions Sahil Siddiq
                   ` (3 subsequent siblings)
  4 siblings, 0 replies; 6+ messages in thread
From: Sahil Siddiq @ 2026-10-26 20:12 UTC (permalink / raw)
  To: jonas, stefan.kristiansson, shorne, naveen, davem, mhiramat
  Cc: pjw, wangruikang, namcao, kees, linux-openrisc,
	linux-trace-kernel, linux-kernel, Sahil Siddiq

Hi,

This is v3 of the patch series to add KProbe and Kretprobe support for
OpenRISC. KProbes was introduced in v1 [1] while Kretprobes was introduced
in v2 [2].

In order to build the kernel with Kprobes and Kretprobes enabled, the
following config options are required:
1. CONFIG_HAVE_KPROBES=y
2. CONFIG_KPROBES=y
3. CONFIG_RETHOOK=y
4. CONFIG_KRETPROBES=y

I tested the generic functionality of Kprobes and Kretprobes using the
tests located at "lib/tests" [3], samples located at "samples/kprobes" [4],
as well as a few test modules that I have published here [5]. The following
options are required to build the samples and tests:
1. CONFIG_SAMPLES=y
2. CONFIG_SAMPLE_KPROBES=m
3. CONFIG_SAMPLE_KRETPROBES=m
4. CONFIG_KPROBES_SANITY_TEST=m

I have also added unit tests at "arch/openrisc/kernel/tests" to verify
that Kprobes work properly when inserted at branch instructions, and
that delay slots are handled correctly. The tests are based on the Kprobe
testsuite added for RISC-V. The following options need to be enabled to
build the tests:
1. CONFIG_KUNIT=y
2. CONFIG_RUNTIME_KERNEL_TESTING_MENU=y
3. CONFIG_OR_KPROBES_KUNIT=m

Below are the results of the tests and sample modules when run in my
environment.

- kretprobe_example:

/home # insmod kretprobe_example.ko 
Planted return probe at kernel_clone: (ptrval)
/home # ls >/dev/null
kernel_clone returned 35 and took 1302450 ns to execute
/home # rmmod kretprobe_example.ko 
kernel_clone returned 36 and took 1121200 ns to execute
kretprobe at (ptrval) unregistered
Missed probing 0 instances of kernel_clone

- test_kprobes:

/home # insmod test_kprobes.ko 
KTAP version 1
1..1
    KTAP version 1
    # Subtest: kprobes_test
    # module: test_kprobes
    1..5
    ok 1 test_kprobe
    ok 2 test_kprobes
    ok 3 test_kprobe_missed
    ok 4 test_kretprobe
    ok 5 test_kretprobes
# kprobes_test: pass:5 fail:0 skip:0 total:5
# Totals: pass:5 fail:0 skip:0 total:5
ok 1 kprobes_test

- openrisc_test_kprobes:

/home # insmod openrisc_test_kprobes.ko 
KTAP version 1
1..1
    KTAP version 1
    # Subtest: kprobes_openrisc
    # module: openrisc_test_kprobes
    1..1
    ok 1 test_kprobe_openrisc
ok 1 kprobes_openrisc

v3 adds a few fixes to the patch series based on Sachiko's review comments [6]. I
have listed out the differences introduced in each iteration in the following emails.

Thanks,
Sahil

[1] https://lkml.org/lkml/2026/4/8/21
[2] https://lkml.org/lkml/2026/10/1/28
[3] https://github.com/torvalds/linux/tree/master/lib/tests
[4] https://github.com/torvalds/linux/tree/master/samples/kprobes
[5] https://github.com/valdaarhun/or-dev
[6] https://sashiko.dev/#/patchset/20260930203129.51048-1-sahilcdq0%40gmail.com

Sahil Siddiq (4):
  openrisc: Add utilities and clean up simulation of instructions
  openrisc: Add KProbes
  openrisc: Add unit tests for KProbes on branch instructions
  openrisc: Add Kretprobes

 arch/openrisc/Kconfig                         |   3 +
 arch/openrisc/Kconfig.debug                   |  30 +-
 arch/openrisc/configs/or1ksim_defconfig       |   2 +
 arch/openrisc/configs/virt_defconfig          |   2 +
 arch/openrisc/include/asm/asm.h               |  22 +
 arch/openrisc/include/asm/break.h             |  19 +
 arch/openrisc/include/asm/cpuinfo.h           |   3 +
 arch/openrisc/include/asm/insn-def.h          |  64 ++-
 arch/openrisc/include/asm/kprobes.h           |  77 ++++
 arch/openrisc/include/asm/spr_defs.h          |   1 +
 arch/openrisc/kernel/Makefile                 |   5 +-
 arch/openrisc/kernel/entry.S                  |  16 +
 arch/openrisc/kernel/insn.c                   |  88 ++++
 arch/openrisc/kernel/kprobes.c                | 426 ++++++++++++++++++
 arch/openrisc/kernel/rethook.c                |  32 ++
 arch/openrisc/kernel/rethook.h                |   8 +
 arch/openrisc/kernel/rethook_trampoline.S     | 111 +++++
 arch/openrisc/kernel/setup.c                  |   4 +
 arch/openrisc/kernel/tests/Makefile           |   3 +
 arch/openrisc/kernel/tests/test_kprobes.c     |  59 +++
 arch/openrisc/kernel/tests/test_kprobes.h     |  24 +
 arch/openrisc/kernel/tests/test_kprobes_asm.S | 157 +++++++
 arch/openrisc/kernel/traps.c                  |  82 ++--
 arch/openrisc/lib/memcpy.c                    |   2 +
 arch/openrisc/lib/memset.S                    |   4 +
 arch/openrisc/mm/fault.c                      |   5 +
 samples/kprobes/kprobe_example.c              |   8 +
 27 files changed, 1206 insertions(+), 51 deletions(-)
 create mode 100644 arch/openrisc/include/asm/asm.h
 create mode 100644 arch/openrisc/include/asm/break.h
 create mode 100644 arch/openrisc/include/asm/kprobes.h
 create mode 100644 arch/openrisc/kernel/insn.c
 create mode 100644 arch/openrisc/kernel/kprobes.c
 create mode 100644 arch/openrisc/kernel/rethook.c
 create mode 100644 arch/openrisc/kernel/rethook.h
 create mode 100644 arch/openrisc/kernel/rethook_trampoline.S
 create mode 100644 arch/openrisc/kernel/tests/Makefile
 create mode 100644 arch/openrisc/kernel/tests/test_kprobes.c
 create mode 100644 arch/openrisc/kernel/tests/test_kprobes.h
 create mode 100644 arch/openrisc/kernel/tests/test_kprobes_asm.S

-- 
2.55.0


^ permalink raw reply	[flat|nested] 6+ messages in thread
* [PATCH v3 1/4] openrisc: Add utilities and clean up simulation of instructions
       [not found] <20260930202744.50489-1-sahilcdq0@gmail.com>
  2026-10-26 20:12 ` [PATCH v3 0/4] openrisc: Add support for KProbes and Kretprobes Sahil Siddiq
@ 2026-10-26 20:12 ` Sahil Siddiq
  2026-10-26 20:12 ` [PATCH v3 2/4] openrisc: Add KProbes Sahil Siddiq
                   ` (2 subsequent siblings)
  4 siblings, 0 replies; 6+ messages in thread
From: Sahil Siddiq @ 2026-10-26 20:12 UTC (permalink / raw)
  To: jonas, stefan.kristiansson, shorne, naveen, davem, mhiramat
  Cc: pjw, wangruikang, namcao, kees, linux-openrisc,
	linux-trace-kernel, linux-kernel, Sahil Siddiq

Introduce new instruction-related utilities and macros for OpenRISC.
This is in preparation for patches that add tracing support such as
KProbes and Kretprobes.

Currently, PC is first updated and then saved in the link register
(r9) when simulating l.jal and l.jalr. This can result in a corrupted
page table (bad page map in process). Fix this by saving PC in r9
before updating it.

Move branch simulation to its own function, simulate_branch(), so it
can be reused. It's already being used by do_illegal_instruction().
It'll also be used by KProbes in the following commit.

Introduce simulate_pc() to simulate l.adrp. KProbes will require this
instruction to be simulated as well. simulate_branch() and simulate_pc()
need to be handled differently since branch instructions change the
value of PC while l.adrp depends on PC but doesn't change its value.

Use a static key to check if delay slots are disabled. Delay slots are
a part of the CPU's configuration and won't change at runtime. Since
they are often enabled in an OpenRISC CPU, using a static key will
reduce the overhead of checking this flag in the default case while
processing KProbes inserted at branch instructions and simulating them.

Link: https://raw.githubusercontent.com/openrisc/doc/master/openrisc-arch-1.4-rev0.pdf
Signed-off-by: Sahil Siddiq <sahilcdq0@gmail.com>
---
Changes v2 -> v3:
- arch/openrisc/kernel/insn.c:
  - (simulate_pc):
    Handle case when rd=0
    Add function to KProbe blacklist
  - (simulate_branch): Likewise
- arch/openrisc/kernel/setup.c:
  - (setup_arch): Set static key before calling paging_init()
- arch/openrisc/kernel/traps.c:
  - (do_trap): Move handling of Kprobes in commit #2

Changes v1 -> v2:
- arch/openrisc/include/asm/cpuinfo.h: Introduce "delay_slot" static key
- arch/openrisc/include/asm/insn-def.h:
   - Use macros instead of union
   - Use better names for macros
   - Use genmask() for masks
- arch/openrisc/kernel/insn.c:
   - Use macros instead of magic values
   - (simulate_pc): Update PC
   - (simulate_branch): Handle rb=r9 in l.jalr simulation
- arch/openrisc/kernel/setup.c: Use "delay slot" static key
- arch/openrisc/kernel/traps.c: Use macros instead of magic values

 arch/openrisc/include/asm/cpuinfo.h  |  3 +
 arch/openrisc/include/asm/insn-def.h | 58 ++++++++++++++++--
 arch/openrisc/include/asm/spr_defs.h |  1 +
 arch/openrisc/kernel/Makefile        |  2 +-
 arch/openrisc/kernel/insn.c          | 88 ++++++++++++++++++++++++++++
 arch/openrisc/kernel/setup.c         |  4 ++
 arch/openrisc/kernel/traps.c         | 53 +++--------------
 7 files changed, 159 insertions(+), 50 deletions(-)
 create mode 100644 arch/openrisc/kernel/insn.c

diff --git a/arch/openrisc/include/asm/cpuinfo.h b/arch/openrisc/include/asm/cpuinfo.h
index 3cfc4cf0b019..d6bb8744eba0 100644
--- a/arch/openrisc/include/asm/cpuinfo.h
+++ b/arch/openrisc/include/asm/cpuinfo.h
@@ -15,6 +15,7 @@
 #ifndef __ASM_OPENRISC_CPUINFO_H
 #define __ASM_OPENRISC_CPUINFO_H
 
+#include <linux/jump_label.h>
 #include <asm/spr.h>
 #include <asm/spr_defs.h>
 
@@ -34,6 +35,8 @@ struct cpuinfo_or1k {
 	u16 coreid;
 };
 
+DECLARE_STATIC_KEY_TRUE(delay_slot);
+
 extern struct cpuinfo_or1k cpuinfo_or1k[NR_CPUS];
 extern void setup_cpuinfo(void);
 
diff --git a/arch/openrisc/include/asm/insn-def.h b/arch/openrisc/include/asm/insn-def.h
index 1e0c028a5b95..ccbda049171f 100644
--- a/arch/openrisc/include/asm/insn-def.h
+++ b/arch/openrisc/include/asm/insn-def.h
@@ -3,13 +3,63 @@
  * Copyright (C) 2025 Chen Miao
  */
 
+#include <asm/spr.h>
+#include <asm/spr_defs.h>
+#include <linux/bits.h>
+
 #ifndef __ASM_OPENRISC_INSN_DEF_H
 #define __ASM_OPENRISC_INSN_DEF_H
 
-/* or1k instructions are always 32 bits. */
-#define	OPENRISC_INSN_SIZE		4
-
 /* or1k nop instruction code */
-#define OPENRISC_INSN_NOP     0x15000000U
+#define OPENRISC_INSN_CSYNC	0x23000000U
+#define OPENRISC_INSN_MACRC	0x18010000U
+#define OPENRISC_MASK_MACRC	0xfc01ffffU
+#define OPENRISC_INSN_MSYNC	0x22000000U
+#define OPENRISC_INSN_NOP	0x15000000U
+#define OPENRISC_INSN_PSYNC	0x22800000U
+#define OPENRISC_INSN_SYS	0x20000000U
+#define OPENRISC_INSN_TRAP	0x21000000U
+
+#define OPENRISC_OPCODE_ADRP	0x02
+#define OPENRISC_OPCODE_BF		0x04
+#define OPENRISC_OPCODE_BNF		0x03
+#define OPENRISC_OPCODE_J		0x00
+#define OPENRISC_OPCODE_JAL		0x01
+#define OPENRISC_OPCODE_JALR	0x12
+#define OPENRISC_OPCODE_JR		0x11
+#define OPENRISC_OPCODE_LWA		0x1b
+#define OPENRISC_OPCODE_MFSPR	0x2d
+#define OPENRISC_OPCODE_MTSPR	0x30
+#define OPENRISC_OPCODE_RFE		0x09
+#define OPENRISC_OPCODE_SWA		0x33
+
+#define OPENRISC_ADRP_IMM_MASK		GENMASK(18, 0)
+#define OPENRISC_ADRP_OFFSET_MASK	GENMASK(31, 13)
+#define OPENRISC_ADRP_IMM_SHIFT		13
+#define OPENRISC_ADRP_REG_MASK		GENMASK(25, 0)
+#define OPENRISC_ADRP_REG_SHIFT		21
+#define OPENRISC_JUMP_IMM_MASK		GENMASK(25, 0)
+#define OPENRISC_JUMP_IMM_SHIFT		2
+#define OPENRISC_JUMP_REG_MASK		GENMASK(15, 11)
+#define OPENRISC_JUMP_REG_SHIFT		11
+
+#define OPENRISC_MASK_SYS	GENMASK(31, 16)
+#define OPENRISC_MASK_TRAP	GENMASK(31, 16)
+#define OPENRISC_MASK_BCODE	GENMASK(15, 0)
+
+#define OPENRISC_OPCODE_MASK	0x3f
+#define OPENRISC_OPCODE_SHIFT	0x1a
+
+struct pt_regs;
+
+#define OPENRISC_INSN_SIZE	4
+
+static __always_inline unsigned char get_6_bit_opcode(unsigned long insn)
+{
+	return (insn >> OPENRISC_OPCODE_SHIFT) & OPENRISC_OPCODE_MASK;
+}
+
+void simulate_pc(struct pt_regs *regs, unsigned long jmp);
+void simulate_branch(struct pt_regs *regs, unsigned long jmp);
 
 #endif /* __ASM_OPENRISC_INSN_DEF_H */
diff --git a/arch/openrisc/include/asm/spr_defs.h b/arch/openrisc/include/asm/spr_defs.h
index f0b6b492e9f4..5d13a9b96263 100644
--- a/arch/openrisc/include/asm/spr_defs.h
+++ b/arch/openrisc/include/asm/spr_defs.h
@@ -179,6 +179,7 @@
 #define SPR_CPUCFGR_OF32S  0x00000080  /* ORFPX32 supported */
 #define SPR_CPUCFGR_OF64S  0x00000100  /* ORFPX64 supported */
 #define SPR_CPUCFGR_OV64S  0x00000200  /* ORVDX64 supported */
+#define SPR_CPUCFGR_ND     0x00000400  /* No delay slot */
 #define SPR_CPUCFGR_RES	   0xfffffc00  /* Reserved */
 
 /*
diff --git a/arch/openrisc/kernel/Makefile b/arch/openrisc/kernel/Makefile
index 19e0eb94f2eb..150779fbf010 100644
--- a/arch/openrisc/kernel/Makefile
+++ b/arch/openrisc/kernel/Makefile
@@ -5,7 +5,7 @@
 
 always-$(KBUILD_BUILTIN)	:= vmlinux.lds
 
-obj-y	:= head.o setup.o or32_ksyms.o process.o dma.o \
+obj-y	:= head.o insn.o setup.o or32_ksyms.o process.o dma.o \
 	   traps.o time.o irq.o entry.o ptrace.o signal.o \
 	   sys_call_table.o unwinder.o cacheinfo.o
 
diff --git a/arch/openrisc/kernel/insn.c b/arch/openrisc/kernel/insn.c
new file mode 100644
index 000000000000..619d8080d822
--- /dev/null
+++ b/arch/openrisc/kernel/insn.c
@@ -0,0 +1,88 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * OpenRISC instruction utils
+ *
+ * Linux architectural port borrowing liberally from similar works of
+ * others.  All original copyrights apply as per the original source
+ * declaration.
+ *
+ * OpenRISC implementation:
+ * Copyright (C) 2026 Sahil Siddiq <sahilcdq0@gmail.com>
+ */
+
+#include <linux/kprobes.h>
+#include <linux/ptrace.h>
+#include <asm/insn-def.h>
+#include <asm/cpuinfo.h>
+
+DEFINE_STATIC_KEY_TRUE(delay_slot);
+
+void simulate_pc(struct pt_regs *regs, unsigned long pc_insn)
+{
+	int page_offset;
+	unsigned int rd, op;
+
+	page_offset = sign_extend32(
+		(pc_insn & OPENRISC_ADRP_IMM_MASK) << OPENRISC_ADRP_IMM_SHIFT, 31);
+	rd = (pc_insn & OPENRISC_ADRP_REG_MASK) >> OPENRISC_ADRP_REG_SHIFT;
+	op = get_6_bit_opcode(pc_insn);
+
+	switch (op) {
+	case OPENRISC_OPCODE_ADRP:
+		if (rd != 0)
+			regs->gpr[rd] = page_offset + (regs->pc & OPENRISC_ADRP_OFFSET_MASK);
+		regs->pc += OPENRISC_INSN_SIZE;
+		return;
+	default:
+		break;
+	}
+}
+NOKPROBE_SYMBOL(simulate_pc)
+
+void simulate_branch(struct pt_regs *regs, unsigned long jmp_insn)
+{
+	int displacement;
+	unsigned int rb, op, link_offset, temp;
+
+	displacement = sign_extend32(
+		((jmp_insn) & OPENRISC_JUMP_IMM_MASK) << OPENRISC_JUMP_IMM_SHIFT, 27);
+	rb = (jmp_insn & OPENRISC_JUMP_REG_MASK) >> OPENRISC_JUMP_REG_SHIFT;
+	op = get_6_bit_opcode(jmp_insn);
+	link_offset = OPENRISC_INSN_SIZE;
+
+	if (static_branch_likely(&delay_slot))
+		link_offset <<= 1;
+
+	switch (op) {
+	case OPENRISC_OPCODE_J: /* l.j */
+		regs->pc += displacement;
+		return;
+	case OPENRISC_OPCODE_JAL: /* l.jal */
+		regs->gpr[9] = regs->pc + link_offset;
+		regs->pc += displacement;
+		return;
+	case OPENRISC_OPCODE_BNF: /* l.bnf */
+		if (regs->sr & SPR_SR_F)
+			regs->pc += link_offset;
+		else
+			regs->pc += displacement;
+		return;
+	case OPENRISC_OPCODE_BF: /* l.bf */
+		if (regs->sr & SPR_SR_F)
+			regs->pc += displacement;
+		else
+			regs->pc += link_offset;
+		return;
+	case OPENRISC_OPCODE_JR: /* l.jr */
+		regs->pc = rb == 0 ? 0 : regs->gpr[rb];
+		return;
+	case OPENRISC_OPCODE_JALR: /* l.jalr */
+		temp = regs->pc + link_offset;
+		regs->pc = rb == 0 ? 0 : regs->gpr[rb];
+		regs->gpr[9] = temp;
+		return;
+	default:
+		break;
+	}
+}
+NOKPROBE_SYMBOL(simulate_branch)
diff --git a/arch/openrisc/kernel/setup.c b/arch/openrisc/kernel/setup.c
index 000a9cc10e6f..9c231b320d45 100644
--- a/arch/openrisc/kernel/setup.c
+++ b/arch/openrisc/kernel/setup.c
@@ -252,6 +252,10 @@ void __init setup_arch(char **cmdline_p)
 	/* perform jump_table sorting before paging_init locks down read only memory */
 	jump_label_init();
 
+	/* determine if the processor supports delay slots */
+	if (mfspr(SPR_CPUCFGR) & SPR_CPUCFGR_ND)
+		static_branch_disable(&delay_slot);
+
 	/* paging_init() sets up the MMU and marks all pages as reserved */
 	paging_init();
 
diff --git a/arch/openrisc/kernel/traps.c b/arch/openrisc/kernel/traps.c
index c195be9cc9fc..a59abbca3555 100644
--- a/arch/openrisc/kernel/traps.c
+++ b/arch/openrisc/kernel/traps.c
@@ -32,6 +32,7 @@
 
 #include <asm/bug.h>
 #include <asm/fpu.h>
+#include <asm/insn-def.h>
 #include <asm/io.h>
 #include <asm/processor.h>
 #include <asm/unwinder.h>
@@ -252,12 +253,12 @@ static inline int in_delay_slot(struct pt_regs *regs)
 	insn = *((unsigned int *)regs->pc);
 	op = insn >> 26;
 	switch (op) {
-	case 0x00: /* l.j */
-	case 0x01: /* l.jal */
-	case 0x03: /* l.bnf */
-	case 0x04: /* l.bf */
-	case 0x11: /* l.jr */
-	case 0x12: /* l.jalr */
+	case OPENRISC_OPCODE_J: /* l.j */
+	case OPENRISC_OPCODE_JAL: /* l.jal */
+	case OPENRISC_OPCODE_BNF: /* l.bnf */
+	case OPENRISC_OPCODE_BF: /* l.bf */
+	case OPENRISC_OPCODE_JR: /* l.jr */
+	case OPENRISC_OPCODE_JALR: /* l.jalr */
 		return 1;
 	default:
 		return 0;
@@ -269,47 +270,9 @@ static inline int in_delay_slot(struct pt_regs *regs)
 
 static inline void adjust_pc(struct pt_regs *regs, unsigned long address)
 {
-	int displacement;
-	unsigned int rb, op, jmp;
-
 	if (unlikely(in_delay_slot(regs))) {
 		/* In delay slot, instruction at pc is a branch, simulate it */
-		jmp = *((unsigned int *)regs->pc);
-
-		displacement = sign_extend32(((jmp) & 0x3ffffff) << 2, 27);
-		rb = (jmp & 0x0000ffff) >> 11;
-		op = jmp >> 26;
-
-		switch (op) {
-		case 0x00: /* l.j */
-			regs->pc += displacement;
-			return;
-		case 0x01: /* l.jal */
-			regs->pc += displacement;
-			regs->gpr[9] = regs->pc + 8;
-			return;
-		case 0x03: /* l.bnf */
-			if (regs->sr & SPR_SR_F)
-				regs->pc += 8;
-			else
-				regs->pc += displacement;
-			return;
-		case 0x04: /* l.bf */
-			if (regs->sr & SPR_SR_F)
-				regs->pc += displacement;
-			else
-				regs->pc += 8;
-			return;
-		case 0x11: /* l.jr */
-			regs->pc = regs->gpr[rb];
-			return;
-		case 0x12: /* l.jalr */
-			regs->pc = regs->gpr[rb];
-			regs->gpr[9] = regs->pc + 8;
-			return;
-		default:
-			break;
-		}
+		simulate_branch(regs, *((unsigned int *)regs->pc));
 	} else {
 		regs->pc += 4;
 	}
-- 
2.55.0


^ permalink raw reply	[flat|nested] 6+ messages in thread
* [PATCH v3 2/4] openrisc: Add KProbes
       [not found] <20260930202744.50489-1-sahilcdq0@gmail.com>
  2026-10-26 20:12 ` [PATCH v3 0/4] openrisc: Add support for KProbes and Kretprobes Sahil Siddiq
  2026-10-26 20:12 ` [PATCH v3 1/4] openrisc: Add utilities and clean up simulation of instructions Sahil Siddiq
@ 2026-10-26 20:12 ` Sahil Siddiq
  2026-10-26 20:26   ` Sahil
  2026-10-26 20:12 ` [PATCH v3 3/4] openrisc: Add unit tests for KProbes on branch instructions Sahil Siddiq
  2026-10-26 20:12 ` [PATCH v3 4/4] openrisc: Add Kretprobes Sahil Siddiq
  4 siblings, 1 reply; 6+ messages in thread
From: Sahil Siddiq @ 2026-10-26 20:12 UTC (permalink / raw)
  To: jonas, stefan.kristiansson, shorne, naveen, davem, mhiramat
  Cc: pjw, wangruikang, namcao, kees, linux-openrisc,
	linux-trace-kernel, linux-kernel, Sahil Siddiq

Add KProbes support for OpenRISC. This work is primarily based
on similar work done for LoongArch, MIPS and RISC-V.

KProbes make it possible to trap at almost any address in the
kernel to collect performance/debugging info.

Signed-off-by: Sahil Siddiq <sahilcdq0@gmail.com>
---
Changes v2 -> v3:
- arch/openrisc/kernel/kprobes.c:
  - (kprobe_local_irq_save): New function
  - (kprobe_local_irq_restore): Likewise
  - (arch_prepare_kprobe): Use copy_from_kernel_nofault()
  - (post_kprobe_handler): Enable preemption before returning early for reentered KProbe
  - (setup_singlestep): Disable IRQs by toggling bits in SR register
  - (kprobe_breakpoint_handler): Use result from get_kernel_nofault()
  - (kprobe_fault_handler):
    Enable preemption after handling reentered KProbe
    Restore IRQs by toggling bits in SR register

Changes v1 -> v2:
- arch/openrisc/include/asm/kprobes.h:
   - (struct prev_kprobe): Add restore_pc
   - (struct kprobe_ctlblk): Move restore_pc from global "struct arch_specific_insn"
- arch/openrisc/kernel/kprobes.c:
   - Use macros instead of magic values
   - Use "get_kernel_nofault" instead of directly dereferencing address
   - (insns_need_simulation): Use "daley slot" static key
   - (arch_prepare_kprobe): Prevent KProbe insertion if instruction in delay slot also requires simulation
   - (save_previous_kprobe): Use "restore_pc"
   - (restore_previous_kprobe): Likewise
   - (post_kprobe_handler): Don't re-enable preemption if KProbe is nested
   - (setup_singlestep): Use "restore_pc"
   - (reenter_kprobe): Return false in case of unrecoverable KProbe
   - (kprobe_singlestep_handler): Enable interrupt in pt_regs->sr
   - (kprobe_fault_handler): Likewise

 arch/openrisc/Kconfig                   |   1 +
 arch/openrisc/configs/or1ksim_defconfig |   2 +
 arch/openrisc/configs/virt_defconfig    |   2 +
 arch/openrisc/include/asm/asm.h         |  22 ++
 arch/openrisc/include/asm/break.h       |  19 ++
 arch/openrisc/include/asm/insn-def.h    |   6 +
 arch/openrisc/include/asm/kprobes.h     |  77 +++++
 arch/openrisc/kernel/Makefile           |   1 +
 arch/openrisc/kernel/entry.S            |  16 +
 arch/openrisc/kernel/kprobes.c          | 426 ++++++++++++++++++++++++
 arch/openrisc/kernel/traps.c            |  29 ++
 arch/openrisc/lib/memcpy.c              |   2 +
 arch/openrisc/lib/memset.S              |   4 +
 arch/openrisc/mm/fault.c                |   5 +
 samples/kprobes/kprobe_example.c        |   8 +
 15 files changed, 620 insertions(+)
 create mode 100644 arch/openrisc/include/asm/asm.h
 create mode 100644 arch/openrisc/include/asm/break.h
 create mode 100644 arch/openrisc/include/asm/kprobes.h
 create mode 100644 arch/openrisc/kernel/kprobes.c

diff --git a/arch/openrisc/Kconfig b/arch/openrisc/Kconfig
index 9156635dd264..d240533b424b 100644
--- a/arch/openrisc/Kconfig
+++ b/arch/openrisc/Kconfig
@@ -27,6 +27,7 @@ config OPENRISC
 	select HAVE_ARCH_JUMP_LABEL
 	select HAVE_ARCH_JUMP_LABEL_RELATIVE
 	select HAVE_PCI
+	select HAVE_KPROBES
 	select HAVE_UID16
 	select HAVE_PAGE_SIZE_8KB
 	select HAVE_REGS_AND_STACK_ACCESS_API
diff --git a/arch/openrisc/configs/or1ksim_defconfig b/arch/openrisc/configs/or1ksim_defconfig
index 769705ac24d5..24d2915e7609 100644
--- a/arch/openrisc/configs/or1ksim_defconfig
+++ b/arch/openrisc/configs/or1ksim_defconfig
@@ -10,7 +10,9 @@ CONFIG_EXPERT=y
 # CONFIG_KALLSYMS is not set
 CONFIG_BUILTIN_DTB_NAME="or1ksim"
 CONFIG_HZ_100=y
+CONFIG_OPENRISC=y
 CONFIG_JUMP_LABEL=y
+CONFIG_KPROBES=y
 CONFIG_MODULES=y
 # CONFIG_BLOCK is not set
 CONFIG_SLUB_TINY=y
diff --git a/arch/openrisc/configs/virt_defconfig b/arch/openrisc/configs/virt_defconfig
index 0b9979b35ca8..2eccb506032f 100644
--- a/arch/openrisc/configs/virt_defconfig
+++ b/arch/openrisc/configs/virt_defconfig
@@ -11,8 +11,10 @@ CONFIG_OPENRISC_HAVE_INST_SEXT=y
 CONFIG_NR_CPUS=8
 CONFIG_SMP=y
 CONFIG_HZ_100=y
+CONFIG_OPENRISC=y
 # CONFIG_OPENRISC_NO_SPR_SR_DSX is not set
 CONFIG_JUMP_LABEL=y
+CONFIG_KPROBES=y
 # CONFIG_COMPAT_BRK is not set
 CONFIG_NET=y
 CONFIG_PACKET=y
diff --git a/arch/openrisc/include/asm/asm.h b/arch/openrisc/include/asm/asm.h
new file mode 100644
index 000000000000..aafe08029b4b
--- /dev/null
+++ b/arch/openrisc/include/asm/asm.h
@@ -0,0 +1,22 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Macros for OpenRISC asm
+ *
+ * Linux architectural port borrowing nearly verbatim from
+ * LoongArch and Arm. All original copyrights apply as per
+ * the original source declaration.
+ */
+
+#ifndef __ASM_ASM_H
+#define __ASM_ASM_H
+
+#ifdef CONFIG_KPROBES
+#define _ASM_NOKPROBE(symbol)			\
+	.pushsection "_kprobe_blacklist", "aw";	\
+	.long symbol;				\
+	.popsection
+#else
+#define _ASM_NOKPROBE(symbol)
+#endif
+
+#endif /* __ASM_ASM_H */
diff --git a/arch/openrisc/include/asm/break.h b/arch/openrisc/include/asm/break.h
new file mode 100644
index 000000000000..04a74d863eef
--- /dev/null
+++ b/arch/openrisc/include/asm/break.h
@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * OpenRISC trap codes used internally by the kernel
+ *
+ * Linux architectural port borrowing liberally from similar works of
+ * others.  All original copyrights apply as per the original source
+ * declaration.
+ *
+ * Modifications for the OpenRISC architecture:
+ * Copyright (C) 2026 Sahil Siddiq <sahilcdq0@gmail.com>
+ */
+
+#ifndef __ASM_BREAK_H
+#define __ASM_BREAK_H
+
+#define BRK_KPROBE_BP       512     /* Kprobe break */
+#define BRK_KPROBE_SSTEPBP  1024    /* Kprobe single-step software implementation */
+
+#endif /* __ASM_BREAK_H */
diff --git a/arch/openrisc/include/asm/insn-def.h b/arch/openrisc/include/asm/insn-def.h
index ccbda049171f..3680c0a94faf 100644
--- a/arch/openrisc/include/asm/insn-def.h
+++ b/arch/openrisc/include/asm/insn-def.h
@@ -54,6 +54,12 @@ struct pt_regs;
 
 #define OPENRISC_INSN_SIZE	4
 
+/* Helpers for working with l.trap */
+static inline unsigned long __emit_trap(unsigned long code)
+{
+	return (code & OPENRISC_MASK_BCODE) | OPENRISC_INSN_TRAP;
+}
+
 static __always_inline unsigned char get_6_bit_opcode(unsigned long insn)
 {
 	return (insn >> OPENRISC_OPCODE_SHIFT) & OPENRISC_OPCODE_MASK;
diff --git a/arch/openrisc/include/asm/kprobes.h b/arch/openrisc/include/asm/kprobes.h
new file mode 100644
index 000000000000..2b5847002141
--- /dev/null
+++ b/arch/openrisc/include/asm/kprobes.h
@@ -0,0 +1,77 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * OpenRISC Linux
+ *
+ * Linux architectural port borrowing liberally from similar works of
+ * others.  All original copyrights apply as per the original source
+ * declaration.
+ *
+ * OpenRISC implementation:
+ * Copyright (C) 2026 Sahil Siddiq <sahilcdq0@gmail.com>
+ */
+
+#ifndef __ASM_OPENRISC_KPROBES_H
+#define __ASM_OPENRISC_KPROBES_H
+
+#include <asm-generic/kprobes.h>
+
+#ifdef CONFIG_KPROBES
+#include <asm/break.h>
+#include <asm/cacheflush.h>
+
+#define	 __ARCH_WANT_KPROBES_INSN_SLOT
+
+struct pt_regs;
+struct kprobe;
+
+typedef u32 kprobe_opcode_t;
+
+/*
+ * MAX_INSN_SIZE is used as the number of slots in an executable
+ * page for single-stepping out of line (SSOL). We need two slots
+ * since we single-step using software breakpoints. The probed
+ * instruction is placed in the first slot with a breakpoint
+ * instruction in the second slot.
+ */
+#define MAX_INSN_SIZE	2
+
+/* Architecture specific copy of original instruction */
+struct arch_specific_insn {
+	/* copy of original instruction */
+	kprobe_opcode_t *insn;
+};
+
+struct prev_kprobe {
+	struct kprobe *kp;
+	unsigned int status;
+	unsigned long restore_pc;
+};
+
+/* per-cpu kprobe control block */
+struct kprobe_ctlblk {
+	unsigned int kprobe_status;
+	unsigned long irq_flags;
+	/* address of next instruction in case of SSOL */
+	unsigned long restore_pc;
+	struct prev_kprobe prev_kprobe;
+};
+
+#define flush_insn_slot(p)		do { } while (0)
+#define kretprobe_blacklist_size	0
+
+void arch_remove_kprobe(struct kprobe *p);
+int kprobe_fault_handler(struct pt_regs *regs, int trapnr);
+bool kprobe_breakpoint_handler(struct pt_regs *regs);
+bool kprobe_singlestep_handler(struct pt_regs *regs);
+#else /* !CONFIG_KPROBES */
+static inline bool kprobe_breakpoint_handler(struct pt_regs *regs)
+{
+	return false;
+}
+
+static inline bool kprobe_singlestep_handler(struct pt_regs *regs)
+{
+	return false;
+}
+#endif /* CONFIG_KPROBES */
+#endif /* __ASM_OPENRISC_KPROBES_H */
diff --git a/arch/openrisc/kernel/Makefile b/arch/openrisc/kernel/Makefile
index 150779fbf010..2ac824867963 100644
--- a/arch/openrisc/kernel/Makefile
+++ b/arch/openrisc/kernel/Makefile
@@ -14,6 +14,7 @@ obj-$(CONFIG_SMP)		+= smp.o sync-timer.o
 obj-$(CONFIG_STACKTRACE)	+= stacktrace.o
 obj-$(CONFIG_MODULES)		+= module.o
 obj-$(CONFIG_OF)		+= prom.o
+obj-$(CONFIG_KPROBES)		+= kprobes.o
 obj-y	+= patching.o
 
 clean:
diff --git a/arch/openrisc/kernel/entry.S b/arch/openrisc/kernel/entry.S
index c7e90b09645e..cd28bf1f7a3b 100644
--- a/arch/openrisc/kernel/entry.S
+++ b/arch/openrisc/kernel/entry.S
@@ -15,6 +15,7 @@
 #include <linux/linkage.h>
 #include <linux/pgtable.h>
 
+#include <asm/asm.h>
 #include <asm/processor.h>
 #include <asm/unistd.h>
 #include <asm/thread_info.h>
@@ -640,6 +641,7 @@ ENTRY(_sys_call_handler)
 	/* r30 is the only register we clobber in the fast path */
 	/* r30 already saved */
 /*	l.sw    PT_GPR30(r1),r30 */
+_ASM_NOKPROBE(_sys_call_handler)
 
 _syscall_check_trace_enter:
 	/* syscalls run with interrupts enabled */
@@ -652,12 +654,14 @@ _syscall_check_trace_enter:
 	l.sfne	r30,r0
 	l.bf	_syscall_trace_enter
 	 l.nop
+_ASM_NOKPROBE(_syscall_check_trace_enter)
 
 _syscall_check:
 	/* Ensure that the syscall number is reasonable */
 	l.sfgeui r11,__NR_syscalls
 	l.bf	_syscall_badsys
 	 l.nop
+_ASM_NOKPROBE(_syscall_check)
 
 _syscall_call:
 	l.movhi r29,hi(sys_call_table)
@@ -668,12 +672,14 @@ _syscall_call:
 
 	l.jalr  r29
 	 l.nop
+_ASM_NOKPROBE(_syscall_call)
 
 _syscall_return:
 	/* All syscalls return here... just pay attention to ret_from_fork
 	 * which does it in a round-about way.
 	 */
 	l.sw    PT_GPR11(r1),r11           // save return value
+_ASM_NOKPROBE(_syscall_return)
 
 #if 0
 _syscall_debug:
@@ -708,6 +714,7 @@ _syscall_check_trace_leave:
 	l.sfne	r30,r0
 	l.bf	_syscall_trace_leave
 	 l.nop
+_ASM_NOKPROBE(_syscall_check_trace_leave)
 
 /* This is where the exception-return code begins... interrupts need to be
  * disabled the rest of the way here because we can't afford to miss any
@@ -744,6 +751,7 @@ _syscall_check_work:
 	/* _work_pending needs to be called with interrupts disabled */
 	l.j	_work_pending
 	 l.nop
+_ASM_NOKPROBE(_syscall_check_work)
 
 _syscall_resume_userspace:
 //	ENABLE_INTERRUPTS(r29)
@@ -800,6 +808,7 @@ _syscall_resume_userspace:
 	l.mtspr r0,r13,SPR_EPCR_BASE
 	l.mtspr r0,r15,SPR_ESR_BASE
 	l.rfe
+_ASM_NOKPROBE(_syscall_resume_userspace)
 
 /* End of hot path!
  * Keep the below tracing and error handling out of the hot path...
@@ -829,6 +838,7 @@ _syscall_trace_enter:
 
 	l.j	_syscall_check
 	 l.lwz	r8,PT_GPR8(r1)
+_ASM_NOKPROBE(_syscall_trace_enter)
 
 _syscall_trace_leave:
 	l.jal	do_syscall_trace_leave
@@ -836,6 +846,7 @@ _syscall_trace_leave:
 
 	l.j	_syscall_check_work
 	 l.nop
+_ASM_NOKPROBE(_syscall_trace_leave)
 
 _syscall_badsys:
 	/* Here we effectively pretend to have executed an imaginary
@@ -845,6 +856,7 @@ _syscall_badsys:
 	 */
 	l.j	_syscall_return
 	 l.addi	r11,r0,-ENOSYS
+_ASM_NOKPROBE(_syscall_badsys)
 
 /******* END SYSCALL HANDLING *******/
 
@@ -870,6 +882,7 @@ EXCEPTION_ENTRY(_trap_handler)
 
 	l.j     _ret_from_exception
 	 l.nop
+_ASM_NOKPROBE(_trap_handler)
 
 /* ---[ 0xf00: Reserved exception ]-------------------------------------- */
 
@@ -1004,6 +1017,8 @@ ENTRY(_ret_from_exception)
 	 l.nop
 	l.j	_resume_userspace
 	 l.nop
+_ASM_NOKPROBE(_ret_from_exception)
+_ASM_NOKPROBE(_ret_from_intr)
 
 ENTRY(ret_from_fork)
 	l.jal	schedule_tail
@@ -1038,6 +1053,7 @@ ENTRY(ret_from_fork)
 
 	l.j	_syscall_return
 	 l.nop
+_ASM_NOKPROBE(ret_from_fork)
 
 /* ========================================================[ switch ] === */
 
diff --git a/arch/openrisc/kernel/kprobes.c b/arch/openrisc/kernel/kprobes.c
new file mode 100644
index 000000000000..0b8762e340d5
--- /dev/null
+++ b/arch/openrisc/kernel/kprobes.c
@@ -0,0 +1,426 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Kernel probes (KProbes) for OpenRISC
+ *
+ * Linux architectural port borrowing liberally from similar works of
+ * others.  All original copyrights apply as per the original source
+ * declaration.
+ *
+ * OpenRISC implementation:
+ * Copyright (C) 2026 Sahil Siddiq <sahilcdq0@gmail.com>
+ */
+
+#include <linux/kprobes.h>
+#include <asm/cpuinfo.h>
+#include <asm/insn-def.h>
+#include <asm/text-patching.h>
+
+DEFINE_PER_CPU(struct kprobe *, current_kprobe);
+DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
+
+#define KPROBE_BP_INSN		__emit_trap(BRK_KPROBE_BP)
+#define KPROBE_SSTEPBP_INSN	__emit_trap(BRK_KPROBE_SSTEPBP)
+
+static bool insn_not_supported(kprobe_opcode_t insn)
+{
+	switch (insn) {
+	case OPENRISC_INSN_CSYNC:
+	case OPENRISC_INSN_MSYNC:
+	case OPENRISC_INSN_PSYNC:
+		return true;
+	}
+
+	if ((insn & OPENRISC_MASK_TRAP) == OPENRISC_INSN_TRAP)
+		return true;
+
+	if ((insn & OPENRISC_MASK_SYS) == OPENRISC_INSN_SYS)
+		return true;
+
+	if ((insn & OPENRISC_MASK_MACRC) == OPENRISC_INSN_MACRC)
+		return true;
+
+	unsigned char opcode = get_6_bit_opcode(insn);
+
+	switch (opcode) {
+	case OPENRISC_OPCODE_RFE:
+	case OPENRISC_OPCODE_LWA:
+	case OPENRISC_OPCODE_MFSPR:
+	case OPENRISC_OPCODE_MTSPR:
+	case OPENRISC_OPCODE_SWA:
+		return true;
+	}
+
+	return false;
+}
+NOKPROBE_SYMBOL(insn_not_supported)
+
+static bool is_branch_insn(kprobe_opcode_t insn)
+{
+	unsigned char opcode = get_6_bit_opcode(insn);
+
+	switch (opcode) {
+	case OPENRISC_OPCODE_BF:
+	case OPENRISC_OPCODE_BNF:
+	case OPENRISC_OPCODE_J:
+	case OPENRISC_OPCODE_JAL:
+	case OPENRISC_OPCODE_JALR:
+	case OPENRISC_OPCODE_JR:
+		return true;
+	}
+
+	return false;
+}
+NOKPROBE_SYMBOL(is_branch_insn)
+
+static bool is_pc_insn(kprobe_opcode_t insn)
+{
+	unsigned char opcode = get_6_bit_opcode(insn);
+
+	if (opcode == OPENRISC_OPCODE_ADRP)
+		return true;
+
+	return false;
+}
+NOKPROBE_SYMBOL(is_pc_insn)
+
+static bool insns_need_simulation(kprobe_opcode_t insn, bool *exec_delay_slot)
+{
+	*exec_delay_slot = false;
+
+	if (is_branch_insn(insn)) {
+		if (static_branch_likely(&delay_slot))
+			*exec_delay_slot = true;
+		return true;
+	}
+
+	if (is_pc_insn(insn))
+		return true;
+
+	return false;
+}
+NOKPROBE_SYMBOL(insns_need_simulation)
+
+int arch_prepare_kprobe(struct kprobe *p)
+{
+	kprobe_opcode_t insn;
+	kprobe_opcode_t prev_insn, next_insn;
+	bool exec_delay_slot = false;
+
+	/* Attempt to probe at unaligned address */
+	if ((unsigned long)p->addr & 0x3)
+		return -EILSEQ;
+
+	if (unlikely(copy_from_kernel_nofault(&insn, p->addr, OPENRISC_INSN_SIZE)))
+		return -EFAULT;
+
+	p->opcode = insn;
+
+	if (insn_not_supported(insn)) {
+		pr_notice("Can't insert KProbe at blacklisted instruction.\n");
+		return -EINVAL;
+	}
+
+	if (copy_from_kernel_nofault(&prev_insn, p->addr - 1,
+			OPENRISC_INSN_SIZE) == 0 && is_branch_insn(prev_insn)) {
+		if (static_branch_likely(&delay_slot)) {
+			pr_notice("Can't insert KProbe in delay slot.\n");
+			return -EINVAL;
+		}
+	}
+
+	if (copy_from_kernel_nofault(&next_insn, p->addr + 1, OPENRISC_INSN_SIZE) == 0 &&
+	    insns_need_simulation(next_insn, &exec_delay_slot) && is_branch_insn(insn)) {
+		if (static_branch_likely(&delay_slot)) {
+			pr_notice("Can't insert KProbe if following instruction is in a delay slot and depends on PC.\n");
+			return -EINVAL;
+		}
+	}
+
+	if (insns_need_simulation(insn, &exec_delay_slot) && !exec_delay_slot) {
+		p->ainsn.insn = NULL;
+	} else {
+		/*
+		 * Single step probed instruction or, in case of branch instructions, single
+		 * step instruction in delay slot.
+		 */
+		p->ainsn.insn = get_insn_slot();
+		if (!p->ainsn.insn)
+			return -ENOMEM;
+
+		if (exec_delay_slot)
+			patch_insn_write(p->ainsn.insn, next_insn);
+		else
+			patch_insn_write(p->ainsn.insn, p->opcode);
+		patch_insn_write(&p->ainsn.insn[1], KPROBE_SSTEPBP_INSN);
+	}
+
+	return 0;
+}
+NOKPROBE_SYMBOL(arch_prepare_kprobe);
+
+void arch_arm_kprobe(struct kprobe *p)
+{
+	patch_insn_write(p->addr, KPROBE_BP_INSN);
+	flush_insn_slot(p);
+}
+NOKPROBE_SYMBOL(arch_arm_kprobe);
+
+void arch_disarm_kprobe(struct kprobe *p)
+{
+	patch_insn_write(p->addr, p->opcode);
+	flush_insn_slot(p);
+}
+NOKPROBE_SYMBOL(arch_disarm_kprobe);
+
+void arch_remove_kprobe(struct kprobe *p)
+{
+	if (p->ainsn.insn) {
+		free_insn_slot(p->ainsn.insn, 0);
+		p->ainsn.insn = NULL;
+	}
+}
+NOKPROBE_SYMBOL(arch_remove_kprobe);
+
+static void set_current_kprobe(struct kprobe *p)
+{
+	__this_cpu_write(current_kprobe, p);
+}
+NOKPROBE_SYMBOL(set_current_kprobe);
+
+static void save_previous_kprobe(struct kprobe_ctlblk *kcb)
+{
+	kcb->prev_kprobe.kp = kprobe_running();
+	kcb->prev_kprobe.status = kcb->kprobe_status;
+	kcb->prev_kprobe.restore_pc = kcb->restore_pc;
+}
+NOKPROBE_SYMBOL(save_previous_kprobe);
+
+static void restore_previous_kprobe(struct kprobe_ctlblk *kcb)
+{
+	kcb->kprobe_status = kcb->prev_kprobe.status;
+	kcb->restore_pc = kcb->prev_kprobe.restore_pc;
+	set_current_kprobe(kcb->prev_kprobe.kp);
+}
+NOKPROBE_SYMBOL(restore_previous_kprobe);
+
+/*
+ * kprobe_local_irq_(save|restore) disable/enable interrupts
+ * on exiting from the exception handler respectively. This is
+ * achieved by toggling the IEE and TEE bits in regs->sr with
+ * the changes taking effect after returning from the exception
+ * handler.
+ *
+ * Interrupts need to be disabled for the period during which an
+ * instruction is single-stepped.
+ */
+static void __kprobes kprobe_local_irq_save(struct kprobe_ctlblk *kcb,
+						struct pt_regs *regs)
+{
+	kcb->irq_flags = regs->sr;
+	regs->sr = (regs->sr & ~(SPR_SR_IEE|SPR_SR_TEE)) | ARCH_IRQ_DISABLED;
+}
+
+static void __kprobes kprobe_local_irq_restore(struct kprobe_ctlblk *kcb,
+						struct pt_regs *regs)
+{
+	regs->sr = kcb->irq_flags;
+}
+
+static void post_kprobe_handler(struct kprobe *cur, struct kprobe_ctlblk *kcb,
+				struct pt_regs *regs)
+{
+	instruction_pointer_set(regs, kcb->restore_pc);
+
+	if (kcb->kprobe_status == KPROBE_REENTER) {
+		restore_previous_kprobe(kcb);
+		preempt_enable_no_resched();
+		return;
+	}
+
+	kcb->kprobe_status = KPROBE_HIT_SSDONE;
+
+	if (cur->post_handler)
+		cur->post_handler(cur, regs, 0);
+
+	reset_current_kprobe();
+	preempt_enable_no_resched();
+}
+NOKPROBE_SYMBOL(post_kprobe_handler);
+
+static void setup_singlestep(struct kprobe *p, struct pt_regs *regs,
+			     struct kprobe_ctlblk *kcb, int reenter)
+{
+	kprobe_opcode_t insn;
+
+	if (reenter) {
+		save_previous_kprobe(kcb);
+		set_current_kprobe(p);
+		kcb->kprobe_status = KPROBE_REENTER;
+	} else {
+		kcb->kprobe_status = KPROBE_HIT_SS;
+	}
+
+	/* Emulate instruction if required. */
+	insn = p->opcode;
+	if (is_pc_insn(insn)) {
+		simulate_pc(regs, insn);
+		kcb->restore_pc = regs->pc;
+		/* No SSOL is required here, so call post-process immediately. */
+		post_kprobe_handler(p, kcb, regs);
+		return;
+	}
+
+	if (is_branch_insn(insn)) {
+		simulate_branch(regs, insn);
+		/* Save target addr before updating PC to SSOL slot */
+		kcb->restore_pc = regs->pc;
+	} else
+		kcb->restore_pc = regs->pc + OPENRISC_INSN_SIZE;
+
+	if (p->ainsn.insn) {
+		/* Disable IRQs before single stepping */
+		kprobe_local_irq_save(kcb, regs);
+		instruction_pointer_set(regs, (unsigned long)p->ainsn.insn);
+	} else {
+		/*
+		 * The instruction is a branch but delay slots are disabled.
+		 * Simply call the post-handler.
+		 */
+		post_kprobe_handler(p, kcb, regs);
+	}
+}
+NOKPROBE_SYMBOL(setup_singlestep);
+
+static bool reenter_kprobe(struct kprobe *p, struct pt_regs *regs,
+			   struct kprobe_ctlblk *kcb)
+{
+	switch (kcb->kprobe_status) {
+	case KPROBE_HIT_SS:
+	case KPROBE_HIT_SSDONE:
+	case KPROBE_HIT_ACTIVE:
+		kprobes_inc_nmissed_count(p);
+		setup_singlestep(p, regs, kcb, 1);
+		break;
+	case KPROBE_REENTER:
+		pr_warn("Unrecoverable KProbe detected.\n");
+		dump_kprobe(p);
+		WARN_ON_ONCE(1);
+		return false;
+	default:
+		WARN_ON(1);
+		return false;
+	}
+
+	return true;
+}
+NOKPROBE_SYMBOL(reenter_kprobe);
+
+bool kprobe_breakpoint_handler(struct pt_regs *regs)
+{
+	struct kprobe *p, *curr_kprobe;
+	struct kprobe_ctlblk *kcb;
+	kprobe_opcode_t *addr = (kprobe_opcode_t *)regs->pc;
+	kprobe_opcode_t insn;
+
+	/*
+	 * We don't want to be preempted for the entire
+	 * duration of kprobe processing.
+	 */
+	preempt_disable();
+
+	kcb = get_kprobe_ctlblk();
+	curr_kprobe = kprobe_running();
+	p = get_kprobe(addr);
+	if (p) {
+		if (curr_kprobe) {
+			if (reenter_kprobe(p, regs, kcb))
+				return true;
+		} else {
+			/* Probe hit */
+			set_current_kprobe(p);
+			kcb->kprobe_status = KPROBE_HIT_ACTIVE;
+			/*
+			 * If there's no pre-handler or it returns 0, continue
+			 * processing the KProbe as usual. A non-zero return
+			 * value implies the saved registers have been modified
+			 * and the execution path might deviate from what's
+			 * expected. Reset the KProbe and return.
+			 */
+			if (!p->pre_handler || !p->pre_handler(p, regs)) {
+				setup_singlestep(p, regs, kcb, 0);
+			} else {
+				reset_current_kprobe();
+				preempt_enable_no_resched();
+			}
+			return true;
+		}
+	}
+
+	/*
+	 * The breakpoint instruction was removed right after we hit it
+	 * possibly by another cpu. If the original instruction was also
+	 * a trap instruction then return to the trap handler for further
+	 * processing, else no further processing is required.
+	 */
+	if (get_kernel_nofault(insn, addr) < 0
+		|| (insn & OPENRISC_MASK_TRAP) != OPENRISC_INSN_TRAP) {
+		preempt_enable_no_resched();
+		return true;
+	}
+
+	preempt_enable_no_resched();
+	return false;
+}
+NOKPROBE_SYMBOL(kprobe_breakpoint_handler);
+
+bool kprobe_singlestep_handler(struct pt_regs *regs)
+{
+	struct kprobe *cur = kprobe_running();
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+	unsigned long addr = instruction_pointer(regs);
+
+	if (cur && (kcb->kprobe_status & (KPROBE_HIT_SS | KPROBE_REENTER)) &&
+	    ((unsigned long)&cur->ainsn.insn[1] == addr)) {
+		/* Single stepping has been completed. Enable IRQs. */
+		kprobe_local_irq_restore(kcb, regs);
+		post_kprobe_handler(cur, kcb, regs);
+		return true;
+	}
+
+	return false;
+}
+NOKPROBE_SYMBOL(kprobe_singlestep_handler);
+
+int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
+{
+	struct kprobe *cur = kprobe_running();
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+
+	switch (kcb->kprobe_status) {
+	case KPROBE_HIT_SS:
+	case KPROBE_REENTER:
+		/*
+		 * The instruction being single-stepped caused a page fault.
+		 * Reset the current KProbe and set PC to the probe's address.
+		 * Then allow the page fault handler to continue as usual.
+		 */
+		instruction_pointer_set(regs, (unsigned long)cur->addr);
+
+		if (kcb->kprobe_status == KPROBE_REENTER)
+			restore_previous_kprobe(kcb);
+		else
+			reset_current_kprobe();
+
+		kprobe_local_irq_restore(kcb, regs);
+		preempt_enable_no_resched();
+		break;
+	}
+
+	return 0;
+}
+NOKPROBE_SYMBOL(kprobe_fault_handler);
+
+int __init arch_init_kprobes(void)
+{
+	return 0;
+}
diff --git a/arch/openrisc/kernel/traps.c b/arch/openrisc/kernel/traps.c
index a59abbca3555..2d6b29ea8c4f 100644
--- a/arch/openrisc/kernel/traps.c
+++ b/arch/openrisc/kernel/traps.c
@@ -30,10 +30,12 @@
 #include <linux/kallsyms.h>
 #include <linux/uaccess.h>
 
+#include <asm/break.h>
 #include <asm/bug.h>
 #include <asm/fpu.h>
 #include <asm/insn-def.h>
 #include <asm/io.h>
+#include <asm/kprobes.h>
 #include <asm/processor.h>
 #include <asm/unwinder.h>
 #include <asm/sections.h>
@@ -216,10 +218,37 @@ asmlinkage void do_trap(struct pt_regs *regs, unsigned long address)
 	if (user_mode(regs)) {
 		force_sig_fault(SIGTRAP, TRAP_BRKPT, (void __user *)regs->pc);
 	} else {
+		unsigned long trap, bcode;
+
+		if (get_kernel_nofault(trap, (unsigned long *)regs->pc) < 0)
+			return;
+
+		/*
+		 * Trap instruction was probably removed and no further processing
+		 * is required.
+		 */
+		if ((trap & OPENRISC_MASK_TRAP) != OPENRISC_INSN_TRAP)
+			return;
+
+		bcode = (trap & OPENRISC_MASK_BCODE);
+		switch (bcode) {
+		case BRK_KPROBE_BP:
+			if (kprobe_breakpoint_handler(regs))
+				return;
+			break;
+		case BRK_KPROBE_SSTEPBP:
+			if (kprobe_singlestep_handler(regs))
+				return;
+			break;
+		default:
+			break;
+		}
+
 		pr_emerg("KERNEL: Illegal trap exception 0x%.8lx\n", regs->pc);
 		die("Die:", regs, SIGILL);
 	}
 }
+NOKPROBE_SYMBOL(do_trap)
 
 asmlinkage void do_unaligned_access(struct pt_regs *regs, unsigned long address)
 {
diff --git a/arch/openrisc/lib/memcpy.c b/arch/openrisc/lib/memcpy.c
index e2af9b510804..701262a40134 100644
--- a/arch/openrisc/lib/memcpy.c
+++ b/arch/openrisc/lib/memcpy.c
@@ -16,6 +16,7 @@
 
 #include <linux/export.h>
 
+#include <linux/kprobes.h>
 #include <linux/string.h>
 
 #ifdef CONFIG_OR1K_1200
@@ -122,4 +123,5 @@ void *memcpy(void *dest, __const void *src, __kernel_size_t n)
 }
 #endif
 
+NOKPROBE_SYMBOL(memcpy);
 EXPORT_SYMBOL(memcpy);
diff --git a/arch/openrisc/lib/memset.S b/arch/openrisc/lib/memset.S
index c3ac2a8b68d3..14e63af12d73 100644
--- a/arch/openrisc/lib/memset.S
+++ b/arch/openrisc/lib/memset.S
@@ -9,6 +9,8 @@
  * Copyright (C) 2015 Olof Kindgren <olof.kindgren@gmail.com>
  */
 
+#include <asm/asm.h>
+
 	.global memset
 	.type	memset, @function
 memset:
@@ -92,3 +94,5 @@ memset:
 
 4:	l.jr		r9
 	 l.ori		r11, r3, 0
+
+_ASM_NOKPROBE(memset)
diff --git a/arch/openrisc/mm/fault.c b/arch/openrisc/mm/fault.c
index 29e232d78d82..5263a832562f 100644
--- a/arch/openrisc/mm/fault.c
+++ b/arch/openrisc/mm/fault.c
@@ -14,6 +14,7 @@
 #include <linux/mm.h>
 #include <linux/interrupt.h>
 #include <linux/extable.h>
+#include <linux/kprobes.h>
 #include <linux/sched/signal.h>
 #include <linux/perf_event.h>
 
@@ -55,6 +56,9 @@ asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long address,
 
 	tsk = current;
 
+	if (kprobe_page_fault(regs, vector))
+		return;
+
 	/*
 	 * We fault-in kernel-space virtual memory on-demand. The
 	 * 'reference' page table is init_mm.pgd.
@@ -351,3 +355,4 @@ asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long address,
 		return;
 	}
 }
+NOKPROBE_SYMBOL(do_page_fault)
diff --git a/samples/kprobes/kprobe_example.c b/samples/kprobes/kprobe_example.c
index 53ec6c8b8c40..84e26ebef70b 100644
--- a/samples/kprobes/kprobe_example.c
+++ b/samples/kprobes/kprobe_example.c
@@ -59,6 +59,10 @@ static int __kprobes handler_pre(struct kprobe *p, struct pt_regs *regs)
 	pr_info("<%s> p->addr = 0x%p, era = 0x%lx, estat = 0x%lx\n",
 		p->symbol_name, p->addr, regs->csr_era, regs->csr_estat);
 #endif
+#ifdef CONFIG_OPENRISC
+	pr_info("<%s> p->addr = 0x%p, pc = 0x%lx, status = 0x%lx\n",
+		p->symbol_name, p->addr, regs->pc, regs->sr);
+#endif
 
 	/* A dump_stack() here will give a stack backtrace */
 	return 0;
@@ -100,6 +104,10 @@ static void __kprobes handler_post(struct kprobe *p, struct pt_regs *regs,
 	pr_info("<%s> p->addr = 0x%p, estat = 0x%lx\n",
 		p->symbol_name, p->addr, regs->csr_estat);
 #endif
+#ifdef CONFIG_OPENRISC
+	pr_info("<%s> p->addr = 0x%p, status = 0x%lx\n",
+		p->symbol_name, p->addr, regs->sr);
+#endif
 }
 
 static int __init kprobe_init(void)
-- 
2.55.0


^ permalink raw reply	[flat|nested] 6+ messages in thread
* [PATCH v3 3/4] openrisc: Add unit tests for KProbes on branch instructions
       [not found] <20260930202744.50489-1-sahilcdq0@gmail.com>
                   ` (2 preceding siblings ...)
  2026-10-26 20:12 ` [PATCH v3 2/4] openrisc: Add KProbes Sahil Siddiq
@ 2026-10-26 20:12 ` Sahil Siddiq
  2026-10-26 20:12 ` [PATCH v3 4/4] openrisc: Add Kretprobes Sahil Siddiq
  4 siblings, 0 replies; 6+ messages in thread
From: Sahil Siddiq @ 2026-10-26 20:12 UTC (permalink / raw)
  To: jonas, stefan.kristiansson, shorne, naveen, davem, mhiramat
  Cc: pjw, wangruikang, namcao, kees, linux-openrisc,
	linux-trace-kernel, linux-kernel, Sahil Siddiq

Tests already exist lib/tests to verify the generic functionality of
KProbes. Add unit tests to verify that KProbes work on instructions
that require simulation in the OpenRISC ISA, and that the corresponding
delay slots are handled correctly.

Signed-off-by: Sahil Siddiq <sahilcdq0@gmail.com>
---
Changes v2 -> v3:
- arch/openrisc/kernel/tests/test_kprobes_asm.S:
  - (test_kprobes_*): Set value in r11 register to 0 prior to running tests
  - (test_kprobes_adrp):
    Place function at page-aligned address
    Use PAGE_SIZE macro instead of magic number
    Move value in r13 to r11 before exiting

Changes v1 -> v2: New commit

 arch/openrisc/Kconfig.debug                   |  30 +++-
 arch/openrisc/kernel/Makefile                 |   1 +
 arch/openrisc/kernel/tests/Makefile           |   3 +
 arch/openrisc/kernel/tests/test_kprobes.c     |  59 +++++++
 arch/openrisc/kernel/tests/test_kprobes.h     |  24 +++
 arch/openrisc/kernel/tests/test_kprobes_asm.S | 157 ++++++++++++++++++
 6 files changed, 273 insertions(+), 1 deletion(-)
 create mode 100644 arch/openrisc/kernel/tests/Makefile
 create mode 100644 arch/openrisc/kernel/tests/test_kprobes.c
 create mode 100644 arch/openrisc/kernel/tests/test_kprobes.h
 create mode 100644 arch/openrisc/kernel/tests/test_kprobes_asm.S

diff --git a/arch/openrisc/Kconfig.debug b/arch/openrisc/Kconfig.debug
index 295942fe3fd5..54110f3a111f 100644
--- a/arch/openrisc/Kconfig.debug
+++ b/arch/openrisc/Kconfig.debug
@@ -1,2 +1,30 @@
 # SPDX-License-Identifier: GPL-2.0-only
-# dummy file, do not delete
+menu "openrisc Testing"
+
+menuconfig RUNTIME_KERNEL_TESTING_MENU
+    bool "openrisc kernel runtime testing"
+    default y
+    help
+      Enable openrisc kernel runtime testing. With this option, one can
+      build and run tests to verify the correctness of relevant components
+      in the kernel at runtime.
+
+if RUNTIME_KERNEL_TESTING_MENU
+
+config OR_KPROBES_KUNIT
+    tristate "KUnit test for kprobes on openrisc"
+    depends on KUNIT
+    depends on KPROBES
+    default KUNIT_ALL_TESTS
+    help
+      Enable testing of KProbes in OpenRISC for instructions that
+      require simulation. When further changes related to probes or
+      tracing are added to OpenRISC's port, these tests can help
+      verify that instruction simulation and processing of delay slots
+      continue to work as expected.
+
+      If unsure, say N
+
+endif # RUNTIME_KERNEL_TESTING_MENU
+
+endmenu # "openrisc Testing"
diff --git a/arch/openrisc/kernel/Makefile b/arch/openrisc/kernel/Makefile
index 2ac824867963..0c1cade09e0c 100644
--- a/arch/openrisc/kernel/Makefile
+++ b/arch/openrisc/kernel/Makefile
@@ -15,6 +15,7 @@ obj-$(CONFIG_STACKTRACE)	+= stacktrace.o
 obj-$(CONFIG_MODULES)		+= module.o
 obj-$(CONFIG_OF)		+= prom.o
 obj-$(CONFIG_KPROBES)		+= kprobes.o
+obj-$(CONFIG_OR_KPROBES_KUNIT)	+= tests/
 obj-y	+= patching.o
 
 clean:
diff --git a/arch/openrisc/kernel/tests/Makefile b/arch/openrisc/kernel/tests/Makefile
new file mode 100644
index 000000000000..9e9693fd3550
--- /dev/null
+++ b/arch/openrisc/kernel/tests/Makefile
@@ -0,0 +1,3 @@
+obj-$(CONFIG_OR_KPROBES_KUNIT)	+= openrisc_test_kprobes.o
+
+openrisc_test_kprobes-objs := test_kprobes.o test_kprobes_asm.o
diff --git a/arch/openrisc/kernel/tests/test_kprobes.c b/arch/openrisc/kernel/tests/test_kprobes.c
new file mode 100644
index 000000000000..a41bdec662e1
--- /dev/null
+++ b/arch/openrisc/kernel/tests/test_kprobes.c
@@ -0,0 +1,59 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * KProbe unit tests for OpenRISC
+ *
+ * Unit tests borrowed liberally from similar work of RISC-V. All
+ * original copyrights apply as per the original source declaration.
+ */
+
+// #include <linux/kernel.h>
+#include <linux/kprobes.h>
+#include <kunit/test.h>
+#include "test_kprobes.h"
+
+static void test_kprobe_openrisc(struct kunit *test)
+{
+	unsigned int num_kprobe = 0;
+	unsigned long (*func)(void);
+	struct kprobe *kp;
+	int i;
+
+	while (test_kprobes_addresses[num_kprobe])
+		num_kprobe++;
+
+	kp = kcalloc(num_kprobe, sizeof(struct kprobe), GFP_KERNEL);
+	KUNIT_EXPECT_TRUE(test, kp);
+	if (!kp)
+		return;
+
+	for (i = 0; i < num_kprobe; ++i) {
+		kp[i].addr = test_kprobes_addresses[i];
+		KUNIT_EXPECT_EQ(test, 0, register_kprobe(&kp[i]));
+	}
+
+	for (i = 0;; ++i) {
+		func = test_kprobes_functions[i];
+		if (!func)
+			break;
+		KUNIT_EXPECT_EQ_MSG(test, KPROBE_TEST_MAGIC, func(), "function %d broken", i);
+	}
+
+	for (i = 0; i < num_kprobe; ++i)
+		unregister_kprobe(&kp[i]);
+	kfree(kp);
+}
+
+static struct kunit_case kprobes_testcases[] = {
+	KUNIT_CASE(test_kprobe_openrisc),
+	{}
+};
+
+static struct kunit_suite kprobes_test_suite = {
+	.name = "kprobes_openrisc",
+	.test_cases = kprobes_testcases,
+};
+
+kunit_test_suites(&kprobes_test_suite);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("KUnit test for OpenRISC KProbes");
diff --git a/arch/openrisc/kernel/tests/test_kprobes.h b/arch/openrisc/kernel/tests/test_kprobes.h
new file mode 100644
index 000000000000..26c26920d430
--- /dev/null
+++ b/arch/openrisc/kernel/tests/test_kprobes.h
@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Unit tests borrowed liberally from similar work of RISC-V. All
+ * original copyrights apply as per the original source declaration.
+ */
+
+#ifndef TEST_KPROBES_H
+#define TEST_KPROBES_H
+
+#define KPROBE_TEST_MAGIC          0xDEADC0DE
+#define KPROBE_TEST_MAGIC_LOWER    0x0000C0DE
+#define KPROBE_TEST_MAGIC_UPPER    0x0000DEAD
+
+#ifndef __ASSEMBLER__
+
+/* array of addresses to install kprobes */
+extern void *test_kprobes_addresses[];
+
+/* array of functions that return KPROBE_TEST_MAGIC */
+extern unsigned long (*test_kprobes_functions[])(void);
+
+#endif /* __ASSEMBLER__ */
+
+#endif /* TEST_KPROBES_H */
diff --git a/arch/openrisc/kernel/tests/test_kprobes_asm.S b/arch/openrisc/kernel/tests/test_kprobes_asm.S
new file mode 100644
index 000000000000..bc87a5fb00d5
--- /dev/null
+++ b/arch/openrisc/kernel/tests/test_kprobes_asm.S
@@ -0,0 +1,157 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * KProbes unit tests for OpenRISC
+ *
+ * Unit tests borrowed liberally from similar work of RISC-V. All
+ * original copyrights apply as per the original source declaration.
+ */
+
+#include <linux/linkage.h>
+#include <asm/asm.h>
+#include <asm/page.h>
+
+#include "test_kprobes.h"
+
+SYM_FUNC_START(test_kprobes_j)
+test_kprobes_j_addr1:
+	l.addi	r11,r0,0
+	l.j	2f
+	l.nop
+1:	l.ori	r13,r13,KPROBE_TEST_MAGIC_LOWER
+	l.addi	r11,r13,0
+	l.jr	r9
+	l.nop
+2:	l.movhi	r13,KPROBE_TEST_MAGIC_UPPER
+test_kprobes_j_addr2:
+	l.j	1b
+	l.nop
+SYM_FUNC_END(test_kprobes_j)
+
+SYM_FUNC_START(test_kprobes_jal)
+	l.addi	r11,r0,0
+	l.addi	r15,r9,0
+test_kprobes_jal_addr1:
+	l.jal	2f
+	l.nop
+1:	l.movhi	r13,KPROBE_TEST_MAGIC_UPPER
+	l.jr	r9
+	l.nop
+test_kprobes_jal_addr2:
+2:	l.jal	1b
+	l.nop
+	l.ori	r13,r13,KPROBE_TEST_MAGIC_LOWER
+	l.addi	r11,r13,0
+	l.addi	r9,r15,0
+	l.jr	r9
+	l.nop
+SYM_FUNC_END(test_kprobes_jal)
+
+SYM_FUNC_START(test_kprobes_jr)
+	l.addi	r11,r0,0
+	l.movhi	r15,hi(2f)
+	l.ori	r15,r15,lo(2f)
+test_kprobes_jr_addr1:
+	l.jr	r15
+	l.nop
+1:	l.ori	r13,r13,KPROBE_TEST_MAGIC_LOWER
+	l.addi	r11,r13,0
+	l.jr	r9
+	l.nop
+2:	l.movhi	r13,KPROBE_TEST_MAGIC_UPPER
+	l.movhi	r15,hi(1b)
+	l.ori	r15,r15,lo(1b)
+test_kprobes_jr_addr2:
+	l.jr	r15
+	l.nop
+SYM_FUNC_END(test_kprobes_jr)
+
+SYM_FUNC_START(test_kprobes_jalr)
+	l.addi	r11,r0,0
+	l.addi	r15,r9,0
+	l.movhi	r17,hi(2f)
+	l.ori	r17,r17,lo(2f)
+test_kprobes_jalr_addr1:
+	l.jalr	r17
+	l.nop
+1:	l.movhi	r13,KPROBE_TEST_MAGIC_UPPER
+	l.jr	r9
+	l.nop
+2:	l.movhi	r17,hi(1b)
+	l.ori	r17,r17,lo(1b)
+test_kprobes_jalr_addr2:
+	l.jalr	r17
+	l.nop
+	l.ori	r13,r13,KPROBE_TEST_MAGIC_LOWER
+	l.addi	r11,r13,0
+	l.addi	r9,r15,0
+	l.jr	r9
+	l.nop
+SYM_FUNC_END(test_kprobes_jalr)
+
+SYM_FUNC_START(test_kprobes_branch)
+	l.addi	r11,r0,0
+	l.addi	r15,r0,1
+	l.addi	r17,r0,0
+	l.sfgts	r15,r17
+test_kprobes_branch_addr1:
+	l.bf	2f
+	l.nop
+1:	l.ori	r13,r13,KPROBE_TEST_MAGIC_LOWER
+	l.addi	r11,r13,0
+	l.jr	r9
+	l.nop
+2:	l.movhi	r13,KPROBE_TEST_MAGIC_UPPER
+	l.sfeq	r15,r17
+test_kprobes_branch_addr2:
+	l.bnf	1b
+	l.nop
+SYM_FUNC_END(test_kprobes_branch)
+
+	.align	PAGE_SIZE
+SYM_FUNC_START(test_kprobes_adrp)
+	l.addi	r11,r0,0
+	l.addi	r13,r0,0
+	l.addi	r15,r9,0
+	l.addi	r17,r0,-PAGE_SIZE
+	l.jal	1f
+	l.nop
+1:	l.and	r19,r9,r17
+test_kprobes_adrp_addr:
+	l.adrp	r21,0
+	l.sfeq	r21,r19
+	l.bnf	2f
+	l.nop
+	l.movhi	r13,KPROBE_TEST_MAGIC_UPPER
+	l.ori	r13,r13,KPROBE_TEST_MAGIC_LOWER
+	l.addi	r11,r13,0
+2:	l.addi	r9,r15,0
+	l.jr	r9
+	l.nop
+SYM_FUNC_END(test_kprobes_adrp)
+
+    .section .rodata
+SYM_DATA_START(test_kprobes_addresses)
+	.word test_kprobes_j_addr1
+	.word test_kprobes_j_addr2
+	.word test_kprobes_jal_addr1
+	.word test_kprobes_jal_addr2
+	.word test_kprobes_jr_addr1
+	.word test_kprobes_jr_addr2
+	.word test_kprobes_jalr_addr1
+	.word test_kprobes_jalr_addr2
+	.word test_kprobes_branch_addr1
+	.word test_kprobes_branch_addr2
+	.word test_kprobes_adrp_addr
+	.word 0
+SYM_DATA_END(test_kprobes_addresses)
+
+    .section .rodata
+SYM_DATA_START(test_kprobes_functions)
+	.word test_kprobes_j
+	.word test_kprobes_jal
+	.word test_kprobes_jr
+	.word test_kprobes_jalr
+	.word test_kprobes_branch
+	.word test_kprobes_adrp
+	.word 0
+SYM_DATA_END(test_kprobes_functions)
-- 
2.55.0


^ permalink raw reply	[flat|nested] 6+ messages in thread
* [PATCH v3 4/4] openrisc: Add Kretprobes
       [not found] <20260930202744.50489-1-sahilcdq0@gmail.com>
                   ` (3 preceding siblings ...)
  2026-10-26 20:12 ` [PATCH v3 3/4] openrisc: Add unit tests for KProbes on branch instructions Sahil Siddiq
@ 2026-10-26 20:12 ` Sahil Siddiq
  4 siblings, 0 replies; 6+ messages in thread
From: Sahil Siddiq @ 2026-10-26 20:12 UTC (permalink / raw)
  To: jonas, stefan.kristiansson, shorne, naveen, davem, mhiramat
  Cc: pjw, wangruikang, namcao, kees, linux-openrisc,
	linux-trace-kernel, linux-kernel, Sahil Siddiq

Add Kretprobes support for OpenRISC. Kretprobes allow a probe to be
fired when a function returns. They are built on top of the generic
rethook framework and also require the KProbe mechanism introduced
in the previous commit. This work is primarily based on similar work
done for RISC-V.

Kretprobes work by inserting a KProbe at a function's entry point.
When the function begins to execute, the KProbe is fired and its
pre-handler replaces the function's return address with that of the
rethook trampoline. The trampoline in turn calls the kretprobe handler.
Control is returned to the original caller following this.

Signed-off-by: Sahil Siddiq <sahilcdq0@gmail.com>
---
Changes v2 -> v3:
- arch/openrisc/kernel/rethook_trampoline.S:
  (save_all_base_regs): Save SR and SP registers
  (restore_all_base_regs): Restore SR register

Changes v1 -> v2: New commit

 arch/openrisc/Kconfig                     |   2 +
 arch/openrisc/kernel/Makefile             |   1 +
 arch/openrisc/kernel/rethook.c            |  32 +++++++
 arch/openrisc/kernel/rethook.h            |   8 ++
 arch/openrisc/kernel/rethook_trampoline.S | 111 ++++++++++++++++++++++
 5 files changed, 154 insertions(+)
 create mode 100644 arch/openrisc/kernel/rethook.c
 create mode 100644 arch/openrisc/kernel/rethook.h
 create mode 100644 arch/openrisc/kernel/rethook_trampoline.S

diff --git a/arch/openrisc/Kconfig b/arch/openrisc/Kconfig
index d240533b424b..82365eb8f574 100644
--- a/arch/openrisc/Kconfig
+++ b/arch/openrisc/Kconfig
@@ -28,6 +28,8 @@ config OPENRISC
 	select HAVE_ARCH_JUMP_LABEL_RELATIVE
 	select HAVE_PCI
 	select HAVE_KPROBES
+	select HAVE_KRETPROBES
+	select HAVE_RETHOOK
 	select HAVE_UID16
 	select HAVE_PAGE_SIZE_8KB
 	select HAVE_REGS_AND_STACK_ACCESS_API
diff --git a/arch/openrisc/kernel/Makefile b/arch/openrisc/kernel/Makefile
index 0c1cade09e0c..e36537cea319 100644
--- a/arch/openrisc/kernel/Makefile
+++ b/arch/openrisc/kernel/Makefile
@@ -15,6 +15,7 @@ obj-$(CONFIG_STACKTRACE)	+= stacktrace.o
 obj-$(CONFIG_MODULES)		+= module.o
 obj-$(CONFIG_OF)		+= prom.o
 obj-$(CONFIG_KPROBES)		+= kprobes.o
+obj-$(CONFIG_RETHOOK)		+= rethook.o rethook_trampoline.o
 obj-$(CONFIG_OR_KPROBES_KUNIT)	+= tests/
 obj-y	+= patching.o
 
diff --git a/arch/openrisc/kernel/rethook.c b/arch/openrisc/kernel/rethook.c
new file mode 100644
index 000000000000..50ef6715d044
--- /dev/null
+++ b/arch/openrisc/kernel/rethook.c
@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Generic return hook for OpenRISC. Depends on KProbes.
+ *
+ * Linux architectural port borrowing liberally from similar works of
+ * others.  All original copyrights apply as per the original source
+ * declaration.
+ *
+ * OpenRISC implementation:
+ * Copyright (C) 2026 Sahil Siddiq <sahilcdq0@gmail.com>
+ */
+
+#include <linux/kprobes.h>
+#include <linux/rethook.h>
+#include "rethook.h"
+
+unsigned long arch_rethook_trampoline_callback(struct pt_regs *regs)
+{
+	return rethook_trampoline_handler(regs, regs->gpr2);
+}
+NOKPROBE_SYMBOL(arch_rethook_trampoline_callback)
+
+void arch_rethook_prepare(struct rethook_node *rhn, struct pt_regs *regs, bool mcount)
+{
+	/* Store original return address and frame pointer */
+	rhn->ret_addr = regs->gpr9;
+	rhn->frame = regs->gpr2;
+
+	/* Set return address to trampoline */
+	regs->gpr9 = (unsigned long)arch_rethook_trampoline;
+}
+NOKPROBE_SYMBOL(arch_rethook_prepare)
diff --git a/arch/openrisc/kernel/rethook.h b/arch/openrisc/kernel/rethook.h
new file mode 100644
index 000000000000..332306a5c380
--- /dev/null
+++ b/arch/openrisc/kernel/rethook.h
@@ -0,0 +1,8 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef __OPENRISC_RETHOOK_H
+#define __OPENRISC_RETHOOK_H
+
+unsigned long arch_rethook_trampoline_callback(struct pt_regs *regs);
+void arch_rethook_prepare(struct rethook_node *rhn, struct pt_regs *regs, bool mcount);
+
+#endif
diff --git a/arch/openrisc/kernel/rethook_trampoline.S b/arch/openrisc/kernel/rethook_trampoline.S
new file mode 100644
index 000000000000..5e8fd5a65222
--- /dev/null
+++ b/arch/openrisc/kernel/rethook_trampoline.S
@@ -0,0 +1,111 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Author: Sahil Siddiq <sahilcdq0@gmail.com>
+ */
+
+#include <linux/linkage.h>
+
+#include <asm/asm.h>
+#include <asm/asm-offsets.h>
+#include <asm/ptrace.h>
+
+	.text
+
+	.macro save_all_base_regs
+	l.sw	PT_GPR2(r1),r2
+	l.sw	PT_GPR3(r1),r3
+	l.sw	PT_GPR4(r1),r4
+	l.sw	PT_GPR5(r1),r5
+	l.sw	PT_GPR6(r1),r6
+	l.sw	PT_GPR7(r1),r7
+	l.sw	PT_GPR8(r1),r8
+	l.sw	PT_GPR9(r1),r9
+	l.sw	PT_GPR10(r1),r10
+	l.sw	PT_GPR11(r1),r11
+	l.sw	PT_GPR12(r1),r12
+	l.sw	PT_GPR13(r1),r13
+	l.sw	PT_GPR14(r1),r14
+	l.sw	PT_GPR15(r1),r15
+	l.sw	PT_GPR16(r1),r16
+	l.sw	PT_GPR17(r1),r17
+	l.sw	PT_GPR18(r1),r18
+	l.sw	PT_GPR19(r1),r19
+	l.sw	PT_GPR20(r1),r20
+	l.sw	PT_GPR21(r1),r21
+	l.sw	PT_GPR22(r1),r22
+	l.sw	PT_GPR23(r1),r23
+	l.sw	PT_GPR24(r1),r24
+	l.sw	PT_GPR25(r1),r25
+	l.sw	PT_GPR26(r1),r26
+	l.sw	PT_GPR27(r1),r27
+	l.sw	PT_GPR28(r1),r28
+	l.sw	PT_GPR29(r1),r29
+	l.sw	PT_GPR30(r1),r30
+	l.sw	PT_GPR31(r1),r31
+	/* Save SR in pt_regs */
+	l.mfspr	r13,r0,SPR_SR
+	l.sw	PT_SR(r1),r13
+	/* Save SP in pt_regs as it was prior to setting up this frame */
+	l.addi	r13,r1,PT_SIZE
+	l.sw	PT_SP(r1),r13
+	.endm
+
+	.macro restore_all_base_regs
+	/* Restore SR from pt_regs */
+	l.lwz	r13,PT_SR(r1)
+	l.mtspr	r0,r13,SPR_SR
+	/*
+	 * r1 doesn't need to be explicitly restored from pt_regs. When
+	 * arch_rethook_trampoline_callback finishes, it restores SP to
+	 * what it was before its frame was set up.
+	 */
+	l.lwz	r2,PT_GPR2(r1)
+	l.lwz	r3,PT_GPR3(r1)
+	l.lwz	r4,PT_GPR4(r1)
+	l.lwz	r5,PT_GPR5(r1)
+	l.lwz	r6,PT_GPR6(r1)
+	l.lwz	r7,PT_GPR7(r1)
+	l.lwz	r8,PT_GPR8(r1)
+	/* Return address in r9 is stale, so don't restore it */
+	l.lwz	r10,PT_GPR10(r1)
+	l.lwz	r11,PT_GPR11(r1)
+	l.lwz	r12,PT_GPR12(r1)
+	l.lwz	r13,PT_GPR13(r1)
+	l.lwz	r14,PT_GPR14(r1)
+	l.lwz	r15,PT_GPR15(r1)
+	l.lwz	r16,PT_GPR16(r1)
+	l.lwz	r17,PT_GPR17(r1)
+	l.lwz	r18,PT_GPR18(r1)
+	l.lwz	r19,PT_GPR19(r1)
+	l.lwz	r20,PT_GPR20(r1)
+	l.lwz	r21,PT_GPR21(r1)
+	l.lwz	r22,PT_GPR22(r1)
+	l.lwz	r23,PT_GPR23(r1)
+	l.lwz	r24,PT_GPR24(r1)
+	l.lwz	r25,PT_GPR25(r1)
+	l.lwz	r26,PT_GPR26(r1)
+	l.lwz	r27,PT_GPR27(r1)
+	l.lwz	r28,PT_GPR28(r1)
+	l.lwz	r29,PT_GPR29(r1)
+	l.lwz	r30,PT_GPR30(r1)
+	l.lwz	r31,PT_GPR31(r1)
+	.endm
+
+SYM_CODE_START(arch_rethook_trampoline)
+	/* Allocate enough space on stack for pt_regs */
+	l.addi	r1,r1,-PT_SIZE
+	save_all_base_regs
+
+	l.addi	r3,r1,0	/* pt_regs */
+	l.jal	arch_rethook_trampoline_callback
+	l.nop
+
+	/* use the result as the return-address */
+	l.addi	r9,r11,0
+
+	restore_all_base_regs
+	l.addi	r1,r1,PT_SIZE
+
+	l.jr	r9
+	l.nop
+SYM_CODE_END(arch_rethook_trampoline)
-- 
2.55.0


^ permalink raw reply	[flat|nested] 6+ messages in thread
* Re: [PATCH v3 2/4] openrisc: Add KProbes
  2026-10-26 20:12 ` [PATCH v3 2/4] openrisc: Add KProbes Sahil Siddiq
@ 2026-10-26 20:26   ` Sahil
  0 siblings, 0 replies; 6+ messages in thread
From: Sahil @ 2026-10-26 20:26 UTC (permalink / raw)
  To: jonas, stefan.kristiansson, shorne, naveen, davem, mhiramat
  Cc: pjw, wangruikang, namcao, kees, linux-openrisc,
	linux-trace-kernel, linux-kernel

Hi,

I have two queries in this commit.

On 10/27/26 1:42 AM, Sahil Siddiq wrote:
> Add KProbes support for OpenRISC. This work is primarily based
> on similar work done for LoongArch, MIPS and RISC-V.
> 
> KProbes make it possible to trap at almost any address in the
> kernel to collect performance/debugging info.
>
> [...]
> diff --git a/arch/openrisc/include/asm/kprobes.h b/arch/openrisc/include/asm/kprobes.h
> new file mode 100644
> index 000000000000..2b5847002141
> --- /dev/null
> +++ b/arch/openrisc/include/asm/kprobes.h
> @@ -0,0 +1,77 @@
> [...]
> +
> +struct prev_kprobe {
> +	struct kprobe *kp;
> +	unsigned int status;
> +	unsigned long restore_pc;
> +};
> +
> +/* per-cpu kprobe control block */
> +struct kprobe_ctlblk {
> +	unsigned int kprobe_status;
> +	unsigned long irq_flags;
> +	/* address of next instruction in case of SSOL */
> +	unsigned long restore_pc;
> +	struct prev_kprobe prev_kprobe;
> +};
> +

There was a review comment from Sashiko about saving "irq_flags" in
"struct prev_kprobe". I am not sure if that's actually required.

My understanding is that a KProbe will be reentered if a probe is hit
before single-stepping (e.g. a probe in the pre-handler) or after it
(e.g. a probe in the post-handler). If a KProbe is reentered before
single-stepping, nothing will be present in kprobe_ctlblk.irq_flags that
requires restoration. So, it doesn't need to be saved in prev_kprobe.
And if the KProbe is reentered after single-stepping, by that point the
value in kprobe_ctlblk.irq_flags should have already been restored (i.e.
IRQs should be reenabled by then) and so it shouldn't need saving in
prev_kprobe.

Could you please let me know if I am missing something, or if my
reasoning is sound?

> [...]
> diff --git a/arch/openrisc/kernel/kprobes.c b/arch/openrisc/kernel/kprobes.c
> new file mode 100644
> index 000000000000..0b8762e340d5
> --- /dev/null
> +++ b/arch/openrisc/kernel/kprobes.c
> @@ -0,0 +1,426 @@
> [...]
> +
> +int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
> +{
> +	struct kprobe *cur = kprobe_running();
> +	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
> +
> +	switch (kcb->kprobe_status) {
> +	case KPROBE_HIT_SS:
> +	case KPROBE_REENTER:
> +		/*
> +		 * The instruction being single-stepped caused a page fault.
> +		 * Reset the current KProbe and set PC to the probe's address.
> +		 * Then allow the page fault handler to continue as usual.
> +		 */
> +		instruction_pointer_set(regs, (unsigned long)cur->addr);
> +

There was another review comment from Sashiko. It stated that in the case
of a page fault which is triggered in the delay slot of a jump-and-link
instruction, resetting PC to the branch instruction can corrupt the state.
It theorized that this is due to the modification made to regs->gpr[9]
(the link register) in "simulate_branch()".

I haven't really understood why the state would get corrupted in this case.
Rewinding PC to the branch instruction implies it'll get executed again.
If it gets re-executed, the value in regs->gpr[9] should also get re-evaluated
and it should hold the correct value after re-execution.

> +		if (kcb->kprobe_status == KPROBE_REENTER)
> +			restore_previous_kprobe(kcb);
> +		else
> +			reset_current_kprobe();
> +
> +		kprobe_local_irq_restore(kcb, regs);
> +		preempt_enable_no_resched();
> +		break;
> +	}
> +
> +	return 0;
> +}
> [...]

Thanks,
Sahil

[1] https://sashiko.dev/#/patchset/20260407185650.79816-1-sahilcdq0%40gmail.com?part=2 (1st comment)
[2] https://sashiko.dev/#/patchset/20260930203129.51048-1-sahilcdq0%40gmail.com?part=2 (6th comment)


^ permalink raw reply	[flat|nested] 6+ messages in thread
end of thread, other threads:[~2026-10-26 20:26 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
     [not found] <20260930202744.50489-1-sahilcdq0@gmail.com>
2026-10-26 20:12 ` [PATCH v3 0/4] openrisc: Add support for KProbes and Kretprobes Sahil Siddiq
2026-10-26 20:12 ` [PATCH v3 1/4] openrisc: Add utilities and clean up simulation of instructions Sahil Siddiq
2026-10-26 20:12 ` [PATCH v3 2/4] openrisc: Add KProbes Sahil Siddiq
2026-10-26 20:26   ` Sahil
2026-10-26 20:12 ` [PATCH v3 3/4] openrisc: Add unit tests for KProbes on branch instructions Sahil Siddiq
2026-10-26 20:12 ` [PATCH v3 4/4] openrisc: Add Kretprobes Sahil Siddiq

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