linux-kernel - [PATCH] kasan: Remove kasan_unpoison_stack_above_sp

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Date:   Mon,  6 Jul 2020 15:35:05 +0100
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Cc:     vincenzo.frascino@....com, mark.rutland@....com,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH] kasan: Remove kasan_unpoison_stack_above_sp_to()

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@...tuozzo.com>
Cc: Alexander Potapenko <glider@...gle.com>
Cc: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@....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