linux-kernel - Re: [PATCH 4/5] arm64: ascii armor the arm64 boot init stack canary

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Message-ID: <CAGXu5j+b2UfdPs1yoweAy=jAFj9UQMGYYy1EjQUCi3JNjZD90A@mail.gmail.com>
Date:   Wed, 24 May 2017 09:16:51 -0700
From:   Kees Cook <keescook@...gle.com>
To:     Rik van Riel <riel@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Daniel Micay <danielmicay@...il.com>,
        "Ted Ts'o" <tytso@....edu>, "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...capital.net>,
        Ingo Molnar <mingo@...nel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        linux-sh <linux-sh@...r.kernel.org>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH 4/5] arm64: ascii armor the arm64 boot init stack canary

On Wed, May 24, 2017 at 8:57 AM,  <riel@...hat.com> wrote:
> From: Rik van Riel <riel@...hat.com>
>
> 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@...hat.com>

Acked-by: Kees Cook <keescook@...omium.org>

-Kees

> ---
>  arch/arm64/include/asm/stackprotector.h | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/arch/arm64/include/asm/stackprotector.h b/arch/arm64/include/asm/stackprotector.h
> index fe5e287dc56b..b86a0865ddf1 100644
> --- a/arch/arm64/include/asm/stackprotector.h
> +++ b/arch/arm64/include/asm/stackprotector.h
> @@ -30,6 +30,7 @@ static __always_inline void boot_init_stack_canary(void)
>         /* Try to get a semi random initial value. */
>         get_random_bytes(&canary, sizeof(canary));
>         canary ^= LINUX_VERSION_CODE;
> +       canary &= CANARY_MASK;
>
>         current->stack_canary = canary;
>         __stack_chk_guard = current->stack_canary;
> --
> 2.9.3
>



-- 
Kees Cook
Pixel Security