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.

[andreyknvl@google.com: fix case when a stack is retrieved from cached_stacks]
Link: https://lkml.kernel.org/r/f50c5f96ef896d7936192c888b0c0a7674e33184.1644943792.git.andreyknvl@google.com
[dan.carpenter@oracle.com: remove unnecessary check in alloc_thread_stack_node()]
Link: https://lkml.kernel.org/r/20220301080706.GB17208@kili
Link: https://lkml.kernel.org/r/698c5ab21743c796d46c15d075b9481825973e34.1643047180.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Marco Elver <elver@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/arm64/include/asm/vmap_stack.h b/arch/arm64/include/asm/vmap_stack.h
index 894e031..2087309 100644 (file)
--- 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 */

diff --git a/kernel/fork.c b/kernel/fork.c
index ce0ffe4..9796897 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -286,11 +286,13 @@ static int alloc_thread_stack_node(struct task_struct *tsk, int node)
                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(struct task_struct *tsk, int node)
                }
 
                tsk->stack_vm_area = s;
-               tsk->stack = s->addr;
+               tsk->stack = stack;
                return 0;
        }
 
@@ -326,8 +328,7 @@ static int alloc_thread_stack_node(struct task_struct *tsk, int node)
         * 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;
 }