[PATCH] kasan: Remove kasan_unpoison_stack_above_sp_to()

[Vincenzo Frascino]

The function kasan_unpoison_stack_above_sp_to() is defined in kasan code
but never used. The function was introduced as part of the commit:

commit 9f7d416c36124667 ("kprobes: Unpoison stack in jprobe_return() for KASAN")

... where it was necessary because x86's jprobe_return() would leave
stale shadow on the stack, and was an oddity in that regard.

Since then, jprobes were removed entirely, and as of commit:

commit 80006dbee674f9fa ("kprobes/x86: Remove jprobe implementation")

... there have been no callers of this function.

Remove the declaration and the implementation.

Cc: Andrey Ryabinin <arya...@virtuozzo.com>
Cc: Alexander Potapenko <gli...@google.com>
Cc: Dmitry Vyukov <dvy...@google.com>
Cc: Andrew Morton <ak...@linux-foundation.org>
Signed-off-by: Vincenzo Frascino <vincenzo...@arm.com>
---
include/linux/kasan.h | 2 --
mm/kasan/common.c | 15 ---------------
2 files changed, 17 deletions(-)

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index 82522e996c76..0ebf2fab8567 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -38,7 +38,6 @@ extern void kasan_disable_current(void);
void kasan_unpoison_shadow(const void *address, size_t size);

void kasan_unpoison_task_stack(struct task_struct *task);
-void kasan_unpoison_stack_above_sp_to(const void *watermark);

void kasan_alloc_pages(struct page *page, unsigned int order);
void kasan_free_pages(struct page *page, unsigned int order);
@@ -101,7 +100,6 @@ void kasan_restore_multi_shot(bool enabled);
static inline void kasan_unpoison_shadow(const void *address, size_t size) {}

static inline void kasan_unpoison_task_stack(struct task_struct *task) {}
-static inline void kasan_unpoison_stack_above_sp_to(const void *watermark) {}

static inline void kasan_enable_current(void) {}
static inline void kasan_disable_current(void) {}
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 757d4074fe28..6339179badb2 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -180,21 +180,6 @@ asmlinkage void kasan_unpoison_task_stack_below(const void *watermark)
kasan_unpoison_shadow(base, watermark - base);
}

-/*
- * Clear all poison for the region between the current SP and a provided
- * watermark value, as is sometimes required prior to hand-crafted asm function
- * returns in the middle of functions.
- */
-void kasan_unpoison_stack_above_sp_to(const void *watermark)
-{
- const void *sp = __builtin_frame_address(0);
- size_t size = watermark - sp;
-
- if (WARN_ON(sp > watermark))
- return;
- kasan_unpoison_shadow(sp, size);
-}
-
void kasan_alloc_pages(struct page *page, unsigned int order)
{
u8 tag;
--
2.27.0

[Mark Rutland]

On Mon, Jul 06, 2020 at 03:35:05PM +0100, Vincenzo Frascino wrote:
> The function kasan_unpoison_stack_above_sp_to() is defined in kasan code
> but never used. The function was introduced as part of the commit:
>
> commit 9f7d416c36124667 ("kprobes: Unpoison stack in jprobe_return() for KASAN")
>
> ... where it was necessary because x86's jprobe_return() would leave
> stale shadow on the stack, and was an oddity in that regard.
>
> Since then, jprobes were removed entirely, and as of commit:
>
> commit 80006dbee674f9fa ("kprobes/x86: Remove jprobe implementation")
>
> ... there have been no callers of this function.
>
> Remove the declaration and the implementation.
>
> Cc: Andrey Ryabinin <arya...@virtuozzo.com>
> Cc: Alexander Potapenko <gli...@google.com>
> Cc: Dmitry Vyukov <dvy...@google.com>
> Cc: Andrew Morton <ak...@linux-foundation.org>
> Signed-off-by: Vincenzo Frascino <vincenzo...@arm.com>

This looks sane to me, and I'm not aware of any cases oputside of
jprobes that would need this, so FWIW:

Reviewed-by: Mark Rutland <mark.r...@arm.com>

Mark.

[Andrey Konovalov]

On Mon, Jul 6, 2020 at 4:35 PM Vincenzo Frascino
<vincenzo...@arm.com> wrote:
>
> The function kasan_unpoison_stack_above_sp_to() is defined in kasan code
> but never used. The function was introduced as part of the commit:
>
> commit 9f7d416c36124667 ("kprobes: Unpoison stack in jprobe_return() for KASAN")
>
> ... where it was necessary because x86's jprobe_return() would leave
> stale shadow on the stack, and was an oddity in that regard.
>
> Since then, jprobes were removed entirely, and as of commit:
>
> commit 80006dbee674f9fa ("kprobes/x86: Remove jprobe implementation")
>
> ... there have been no callers of this function.
>
> Remove the declaration and the implementation.
>
> Cc: Andrey Ryabinin <arya...@virtuozzo.com>
> Cc: Alexander Potapenko <gli...@google.com>
> Cc: Dmitry Vyukov <dvy...@google.com>
> Cc: Andrew Morton <ak...@linux-foundation.org>
> Signed-off-by: Vincenzo Frascino <vincenzo...@arm.com>

Reviewed-by: Andrey Konovalov <andre...@google.com>

Thanks!

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