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Message-ID: <201910312046.53A31D394@keescook>
Date: Thu, 31 Oct 2019 20:47:04 -0700
From: Kees Cook <keescook@...omium.org>
To: samitolvanen@...gle.com
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@...glegroups.com,
kernel-hardening@...ts.openwall.com,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 04/17] arm64: kernel: avoid x18 __cpu_soft_restart
On Thu, Oct 31, 2019 at 09:46:24AM -0700, samitolvanen@...gle.com wrote:
> From: Ard Biesheuvel <ard.biesheuvel@...aro.org>
>
> The code in __cpu_soft_restart() uses x18 as an arbitrary temp register,
> which will shortly be disallowed. So use x8 instead.
>
> Link: https://patchwork.kernel.org/patch/9836877/
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
This one is easy to validate! ;)
Reviewed-by: Kees Cook <keescook@...omium.org>
-Kees
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> Reviewed-by: Mark Rutland <mark.rutland@....com>
> ---
> arch/arm64/kernel/cpu-reset.S | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/kernel/cpu-reset.S b/arch/arm64/kernel/cpu-reset.S
> index 6ea337d464c4..32c7bf858dd9 100644
> --- a/arch/arm64/kernel/cpu-reset.S
> +++ b/arch/arm64/kernel/cpu-reset.S
> @@ -42,11 +42,11 @@ ENTRY(__cpu_soft_restart)
> mov x0, #HVC_SOFT_RESTART
> hvc #0 // no return
>
> -1: mov x18, x1 // entry
> +1: mov x8, x1 // entry
> mov x0, x2 // arg0
> mov x1, x3 // arg1
> mov x2, x4 // arg2
> - br x18
> + br x8
> ENDPROC(__cpu_soft_restart)
>
> .popsection
> --
> 2.24.0.rc0.303.g954a862665-goog
>
--
Kees Cook
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