linux-kernel - Re: [PATCH v3 05/17] add support for Clang's Shadow Call Stack (SCS)

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Date:   Fri, 1 Nov 2019 09:28:21 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Dave Martin <Dave.Martin@....com>,
        Laura Abbott <labbott@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Jann Horn <jannh@...gle.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 05/17] add support for Clang's Shadow Call Stack (SCS)

On Thu, Oct 31, 2019 at 8:51 PM Kees Cook <keescook@...omium.org> wrote:
> > +/* A random number to mark the end of the shadow stack. */
> > +#define SCS_END_MAGIC        0xaf0194819b1635f6UL
>
> Is 0xaf.... non-canonical for arm64? While "random", it should also
> likely be an "impossible" value to find on the call stack.

Agreed, and yes, this is non-canonical for arm64 and AFAIK all 64-bit
architectures the kernel supports. I'll add a note about it.

Sami