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Subject[PATCH mm v3 23/38] kasan, arm64: reset pointer tags of vmapped stacks
Date
From: Andrey Konovalov <andreyknvl@google.com>

Once tag-based KASAN modes start tagging vmalloc() allocations,
kernel stacks start getting tagged if CONFIG_VMAP_STACK is enabled.

Reset the tag of kernel stack pointers after allocation in
arch_alloc_vmap_stack().

For SW_TAGS KASAN, when CONFIG_KASAN_STACK is enabled, the
instrumentation can't handle the SP register being tagged.

For HW_TAGS KASAN, there's no instrumentation-related issues. However,
the impact of having a tagged SP register needs to be properly evaluated,
so keep it non-tagged for now.

Note, that the memory for the stack allocation still gets tagged to
catch vmalloc-into-stack out-of-bounds accesses.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

---

Changes v2->v3:
- Add this patch.
---
arch/arm64/include/asm/vmap_stack.h | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/vmap_stack.h b/arch/arm64/include/asm/vmap_stack.h
index 894e031b28d2..20873099c035 100644
--- a/arch/arm64/include/asm/vmap_stack.h
+++ b/arch/arm64/include/asm/vmap_stack.h
@@ -17,10 +17,13 @@
*/
static inline unsigned long *arch_alloc_vmap_stack(size_t stack_size, int node)
{
+ void *p;
+
BUILD_BUG_ON(!IS_ENABLED(CONFIG_VMAP_STACK));

- return __vmalloc_node(stack_size, THREAD_ALIGN, THREADINFO_GFP, node,
+ p = __vmalloc_node(stack_size, THREAD_ALIGN, THREADINFO_GFP, node,
__builtin_return_address(0));
+ return kasan_reset_tag(p);
}

#endif /* __ASM_VMAP_STACK_H */
--
2.25.1
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