[PATCH v2 0/2] cleanup {COMPAT_,}SET_PERSONALITY

[PATCH v2 0/2] cleanup {COMPAT_,}SET_PERSONALITY

[Yury Norov]

This patchset is the result of discussion:
https://lkml.org/lkml/2017/7/31/454

First patch introduces MMCF flags for mm_context_t ->flags to separate it from
TIF ones. And second patch moves personality-related setup code from
SET_PERSONALITY() to the helper.

Yury Norov (2):
  arm64: introduce separated bits for mm_context_t flags
  arm64: cleanup {COMPAT_,}SET_PERSONALITY() macro

 arch/arm64/include/asm/elf.h         | 7 +++++--
 arch/arm64/include/asm/mmu.h         | 2 ++
 arch/arm64/include/asm/thread_info.h | 3 +++
 arch/arm64/kernel/probes/uprobes.c   | 2 +-
 arch/arm64/kernel/process.c          | 8 ++++++++
 5 files changed, 19 insertions(+), 3 deletions(-)

-- 
2.11.0

[PATCH 1/2] arm64: introduce separated bits for mm_context_t flags

[Yury Norov]

Currently mm->context.flags field uses thread_info flags which is not
the best idea for many reasons. For example, mm_context_t doesn't need
most of thread_info flags. And it would be difficult to add new mm-related
flag if needed because it may easily interfere with TIF ones.

To deal with it, the new MMCF_AARCH32 flag is introduced for
mm_context_t->flags, where MMCF prefix stands for mm_context_t flags.
Also, mm_context_t flag doesn't require atomicity and ordering of the
access, so using set/clear_bit() is replaced with simple masks.

RFC: https://lkml.org/lkml/2017/7/31/454
v1:
 - changed the MMCF_AARCH32 bit number from 0x1 to 0x0 and added comment
v2:
 - using set/clear_bit() is replaced with simple masks.

Signed-off-by: Yury Norov <ynorov@caviumnetworks.com>
---
 arch/arm64/include/asm/elf.h       | 4 ++--
 arch/arm64/include/asm/mmu.h       | 2 ++
 arch/arm64/kernel/probes/uprobes.c | 2 +-
 3 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
index 3288c2b36731..517b9ff0456c 100644
--- a/arch/arm64/include/asm/elf.h
+++ b/arch/arm64/include/asm/elf.h
@@ -139,7 +139,7 @@ typedef struct user_fpsimd_state elf_fpregset_t;
 
 #define SET_PERSONALITY(ex)						\
 ({									\
-	clear_bit(TIF_32BIT, &current->mm->context.flags);		\
+	current->mm->context.flags = 0;					\
 	clear_thread_flag(TIF_32BIT);					\
 	current->personality &= ~READ_IMPLIES_EXEC;			\
 })
@@ -195,7 +195,7 @@ typedef compat_elf_greg_t		compat_elf_gregset_t[COMPAT_ELF_NGREG];
  */
 #define COMPAT_SET_PERSONALITY(ex)					\
 ({									\
-	set_bit(TIF_32BIT, &current->mm->context.flags);		\
+	current->mm->context.flags = MMCF_AARCH32;			\
 	set_thread_flag(TIF_32BIT);					\
  })
 #define COMPAT_ARCH_DLINFO
diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h
index 5468c834b072..e4c474c6501e 100644
--- a/arch/arm64/include/asm/mmu.h
+++ b/arch/arm64/include/asm/mmu.h
@@ -16,6 +16,8 @@
 #ifndef __ASM_MMU_H
 #define __ASM_MMU_H
 
+#define MMCF_AARCH32	0x1	/* MM hosts AArch32 executables */
+
 typedef struct {
 	atomic64_t	id;
 	void		*vdso;
diff --git a/arch/arm64/kernel/probes/uprobes.c b/arch/arm64/kernel/probes/uprobes.c
index 26c998534dca..636ca0119c0e 100644
--- a/arch/arm64/kernel/probes/uprobes.c
+++ b/arch/arm64/kernel/probes/uprobes.c
@@ -40,7 +40,7 @@ int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe, struct mm_struct *mm,
 	probe_opcode_t insn;
 
 	/* TODO: Currently we do not support AARCH32 instruction probing */
-	if (test_bit(TIF_32BIT, &mm->context.flags))
+	if (mm->context.flags & MMCF_AARCH32)
 		return -ENOTSUPP;
 	else if (!IS_ALIGNED(addr, AARCH64_INSN_SIZE))
 		return -EINVAL;
-- 
2.11.0

[PATCH 2/2] arm64: cleanup {COMPAT_,}SET_PERSONALITY() macro

[Yury Norov]

There is some work that should be done after setting the personality.
Currently it's done in the macro, which is not the best idea.

In this patch new arch_setup_new_exec() routine is introduced, and all
setup code is moved there, as suggested by Catalin:
https://lkml.org/lkml/2017/8/4/494

v2:
 - don't move clearing READ_IMPLIES_EXEC flag from SET_PERSONALITY()

Signed-off-by: Yury Norov <ynorov@caviumnetworks.com>
CC: Pratyush Anand <panand@redhat.com>
CC: Catalin Marinas <catalin.marinas@arm.com>
---
 arch/arm64/include/asm/elf.h         | 7 +++++--
 arch/arm64/include/asm/thread_info.h | 3 +++
 arch/arm64/kernel/process.c          | 8 ++++++++
 3 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
index 517b9ff0456c..9c4434b8a9a8 100644
--- a/arch/arm64/include/asm/elf.h
+++ b/arch/arm64/include/asm/elf.h
@@ -137,9 +137,13 @@ typedef struct user_fpsimd_state elf_fpregset_t;
  */
 #define ELF_PLAT_INIT(_r, load_addr)	(_r)->regs[0] = 0
 
+/*
+ * Don't modify this macro unless you add new personality.
+ * All personality-related setup should be done at proper place.
+ * If not sure, consider the arch_setup_new_exec() function.
+ */
 #define SET_PERSONALITY(ex)						\
 ({									\
-	current->mm->context.flags = 0;					\
 	clear_thread_flag(TIF_32BIT);					\
 	current->personality &= ~READ_IMPLIES_EXEC;			\
 })
@@ -195,7 +199,6 @@ typedef compat_elf_greg_t		compat_elf_gregset_t[COMPAT_ELF_NGREG];
  */
 #define COMPAT_SET_PERSONALITY(ex)					\
 ({									\
-	current->mm->context.flags = MMCF_AARCH32;			\
 	set_thread_flag(TIF_32BIT);					\
  })
 #define COMPAT_ARCH_DLINFO
diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
index 46c3b93cf865..c823d2f12b4c 100644
--- a/arch/arm64/include/asm/thread_info.h
+++ b/arch/arm64/include/asm/thread_info.h
@@ -68,6 +68,9 @@ struct thread_info {
 #define thread_saved_fp(tsk)	\
 	((unsigned long)(tsk->thread.cpu_context.fp))
 
+void arch_setup_new_exec(void);
+#define arch_setup_new_exec     arch_setup_new_exec
+
 #endif
 
 /*
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 659ae8094ed5..e99012c4803a 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -417,3 +417,11 @@ unsigned long arch_randomize_brk(struct mm_struct *mm)
 	else
 		return randomize_page(mm->brk, SZ_1G);
 }
+
+/*
+ * Called immediately after a successful exec.
+ */
+void arch_setup_new_exec(void)
+{
+	current->mm->context.flags = is_compat_task() ? MMCF_AARCH32 : 0;
+}
-- 
2.11.0

Re: [PATCH v2 0/2] cleanup {COMPAT_,}SET_PERSONALITY

[Catalin Marinas]

On Sun, Aug 20, 2017 at 01:20:46PM +0300, Yury Norov wrote:
> This patchset is the result of discussion:
> https://lkml.org/lkml/2017/7/31/454
> 
> First patch introduces MMCF flags for mm_context_t ->flags to separate it from
> TIF ones. And second patch moves personality-related setup code from
> SET_PERSONALITY() to the helper.
> 
> Yury Norov (2):
>   arm64: introduce separated bits for mm_context_t flags
>   arm64: cleanup {COMPAT_,}SET_PERSONALITY() macro

Patches queued for 4.14. Thanks.

-- 
Catalin