[052/114] kasan, arm64: reset pointer tags of vmapped stacks

Commit Message

Andrew Morton March 25, 2022, 1:11 a.m. UTC

From: Andrey Konovalov <[e-mail]>
Subject: kasan, arm64: reset pointer tags of vmapped stacks

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.

[[e-mail]: fix case when a stack is retrieved from cached_stacks]
  Link: https://lkml.kernel.org/r/f5[e-mail]
[[e-mail]: remove unnecessary check in alloc_thread_stack_node()]
  Link: https://lkml.kernel.org/r/20220301080706.GB17208@kili
Link: https://lkml.kernel.org/r/69[e-mail]
Signed-off-by: Andrey Konovalov <[e-mail]>
Signed-off-by: Dan Carpenter <[e-mail]>
Acked-by: Catalin Marinas <[e-mail]>
Acked-by: Marco Elver <[e-mail]>
Reviewed-by: Marco Elver <[e-mail]>
Cc: Alexander Potapenko <[e-mail]>
Cc: Andrey Ryabinin <[e-mail]>
Cc: Dmitry Vyukov <[e-mail]>
Cc: Evgenii Stepanov <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Peter Collingbourne <[e-mail]>
Cc: Vincenzo Frascino <[e-mail]>
Cc: Will Deacon <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 arch/arm64/include/asm/vmap_stack.h |    5 ++++-
 kernel/fork.c                       |   11 ++++++-----
 2 files changed, 10 insertions(+), 6 deletions(-)

Patch

--- a/arch/arm64/include/asm/vmap_stack.h~kasan-arm64-reset-pointer-tags-of-vmapped-stacks
+++ a/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 */
--- a/kernel/fork.c~kasan-arm64-reset-pointer-tags-of-vmapped-stacks
+++ a/kernel/fork.c
@@ -286,11 +286,13 @@  static int alloc_thread_stack_node(struc
 		if (!s)
 			continue;
 
-		/* Mark stack accessible for KASAN. */
+		/* Reset stack metadata. */
 		kasan_unpoison_range(s->addr, THREAD_SIZE);
 
+		stack = kasan_reset_tag(s->addr);
+
 		/* Clear stale pointers from reused stack. */
-		memset(s->addr, 0, THREAD_SIZE);
+		memset(stack, 0, THREAD_SIZE);
 
 		if (memcg_charge_kernel_stack(s)) {
 			vfree(s->addr);
@@ -298,7 +300,7 @@  static int alloc_thread_stack_node(struc
 		}
 
 		tsk->stack_vm_area = s;
-		tsk->stack = s->addr;
+		tsk->stack = stack;
 		return 0;
 	}
 
@@ -326,8 +328,7 @@  static int alloc_thread_stack_node(struc
 	 * so cache the vm_struct.
 	 */
 	tsk->stack_vm_area = vm;
-	if (stack)
-		stack = kasan_reset_tag(stack);
+	stack = kasan_reset_tag(stack);
 	tsk->stack = stack;
 	return 0;
 }