Re: [PATCH 2/4] kasan: added functions for unpoisoning stack variables

Dmitry Vyukov
2017-07-10T08:46:53Z

On Fri, Jul 7, 2017 at 12:01 AM, Greg Hackmann <ghackmann@google.com> wrote:
> From: Alexander Potapenko <glider@google.com>
>
> As a code-size optimization, LLVM builds since r279383 may
> bulk-manipulate the shadow region when (un)poisoning large memory
> blocks. This requires new callbacks that simply do an uninstrumented
> memset().
>
> This fixes linking the Clang-built kernel when using KASAN.
>
> Signed-off-by: Alexander Potapenko <glider@google.com>
> [ghackmann@google.com: fix memset() parameters, and tweak
> commit message to describe new callbacks]
> Signed-off-by: Greg Hackmann <ghackmann@google.com>
> ---
> mm/kasan/kasan.c | 15 +++++++++++++++
> 1 file changed, 15 insertions(+)
>
> diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
> index 892b626f564b..89911e5c69f9 100644
> --- a/mm/kasan/kasan.c
> +++ b/mm/kasan/kasan.c
> @@ -828,6 +828,21 @@ void __asan_allocas_unpoison(const void *stack_top, const void *stack_bottom)
> }
> EXPORT_SYMBOL(__asan_allocas_unpoison);
>
> +/* Emitted by the compiler to [un]poison local variables. */
> +#define DEFINE_ASAN_SET_SHADOW(byte) \
> + void __asan_set_shadow_##byte(const void *addr, size_t size) \
> + { \
> + __memset((void *)addr, 0x##byte, size); \
> + } \
> + EXPORT_SYMBOL(__asan_set_shadow_##byte)
> +
> +DEFINE_ASAN_SET_SHADOW(00);
> +DEFINE_ASAN_SET_SHADOW(f1);
> +DEFINE_ASAN_SET_SHADOW(f2);
> +DEFINE_ASAN_SET_SHADOW(f3);
> +DEFINE_ASAN_SET_SHADOW(f5);
> +DEFINE_ASAN_SET_SHADOW(f8);
> +
> #ifdef CONFIG_MEMORY_HOTPLUG
> static int kasan_mem_notifier(struct notifier_block *nb,
> unsigned long action, void *data)

Reviewed-by: Dmitry Vyukov <dvyukov@google.com>