Re: [PATCH 3/5] x86: ascii armor the x86_64 boot init stack canary

[Kees Cook]

On Wed, May 24, 2017 at 8:57 AM,  <riel@xxxxxxxxxx> wrote:
> From: Rik van Riel <riel@xxxxxxxxxx>
>
> Use the ascii-armor canary to prevent unterminated C string overflows
> from being able to successfully overwrite the canary, even if they
> somehow obtain the canary value.
>
> Inspired by execshield ascii-armor and Daniel Micay's linux-hardened tree.
>
> Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>

Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>

-Kees

> ---
>  arch/x86/include/asm/stackprotector.h | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/arch/x86/include/asm/stackprotector.h b/arch/x86/include/asm/stackprotector.h
> index dcbd9bcce714..8abedf1d650e 100644
> --- a/arch/x86/include/asm/stackprotector.h
> +++ b/arch/x86/include/asm/stackprotector.h
> @@ -74,6 +74,7 @@ static __always_inline void boot_init_stack_canary(void)
>         get_random_bytes(&canary, sizeof(canary));
>         tsc = rdtsc();
>         canary += tsc + (tsc << 32UL);
> +       canary &= CANARY_MASK;
>
>         current->stack_canary = canary;
>  #ifdef CONFIG_X86_64
> --
> 2.9.3
>



-- 
Kees Cook
Pixel Security