linux-kernel - Re: [PATCH 1/2] scs: switch to vmapped shadow stacks

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Message-ID: <202010221538.9FA560D5B0@keescook>
Date:   Thu, 22 Oct 2020 15:38:41 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        James Morse <james.morse@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] scs: switch to vmapped shadow stacks

On Thu, Oct 22, 2020 at 01:23:54PM -0700, Sami Tolvanen wrote:
> The kernel currently uses kmem_cache to allocate shadow call stacks,
> which means an overflow may not be immediately detected and can
> potentially result in another task's shadow stack to be overwritten.
> 
> This change switches SCS to use virtually mapped shadow stacks,
> which increases shadow stack size to a full page and provides more
> robust overflow detection similarly to VMAP_STACK.
> 
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>

Thanks! I much prefer this to kmem. :)

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

-- 
Kees Cook