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

[Andrey Ryabinin]

On 07/07/2017 01:01 AM, Greg Hackmann wrote:
> From: Alexander Potapenko <glider@xxxxxxxxxx>
> 
> 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@xxxxxxxxxx>
> [ghackmann@xxxxxxxxxx: fix memset() parameters, and tweak
>  commit message to describe new callbacks]
> Signed-off-by: Greg Hackmann <ghackmann@xxxxxxxxxx>
> ---
>  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);

I think we can remove f8 as it should be used only by use-after-return instrumentation.
We don't use it in the kernel

> +
>  #ifdef CONFIG_MEMORY_HOTPLUG
>  static int kasan_mem_notifier(struct notifier_block *nb,
>  			unsigned long action, void *data)
>