linux-kernel - Re: [PATCH v6 09/15] arm64: reserve x18 from general allocation with SCS

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Date:   Thu, 16 Jan 2020 17:37:40 +0000
From:   Will Deacon <will@...nel.org>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Dave Martin <Dave.Martin@....com>,
        Kees Cook <keescook@...omium.org>,
        Laura Abbott <labbott@...hat.com>,
        Marc Zyngier <maz@...nel.org>,
        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@...glegroups.com,
        kernel-hardening@...ts.openwall.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 09/15] arm64: reserve x18 from general allocation with
 SCS

On Fri, Dec 06, 2019 at 02:13:45PM -0800, Sami Tolvanen wrote:
> Reserve the x18 register from general allocation when SCS is enabled,
> because the compiler uses the register to store the current task's
> shadow stack pointer. Note that all external kernel modules must also be
> compiled with -ffixed-x18 if the kernel has SCS enabled.
> 
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Reviewed-by: Kees Cook <keescook@...omium.org>
> ---
>  arch/arm64/Makefile | 4 ++++
>  1 file changed, 4 insertions(+)

Acked-by: Will Deacon <will@...nel.org>

Will