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 <aryabinin@xxxxxxxxxxxxx>
> Cc: Alexander Potapenko <glider@xxxxxxxxxx>
> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
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.rutland@xxxxxxx>
Mark.
> ---
> 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
>
