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Message-ID: <CABCJKud7bJOQqyve9=niSP62H0WTrCk5ZAmAcD2-KR=vf_gn0Q@mail.gmail.com>
Date: Fri, 18 Oct 2019 10:05:18 -0700
From: Sami Tolvanen <samitolvanen@...gle.com>
To: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: Will Deacon <will@...nel.org>, Catalin Marinas <catalin.marinas@....com>,
Steven Rostedt <rostedt@...dmis.org>, Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Dave Martin <Dave.Martin@....com>, Kees Cook <keescook@...omium.org>,
Laura Abbott <labbott@...hat.com>, Mark Rutland <mark.rutland@....com>,
clang-built-linux <clang-built-linux@...glegroups.com>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Linux ARM <linux-arm-kernel@...ts.infradead.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 13/18] arm64: preserve x18 when CPU is suspended
On Fri, Oct 18, 2019 at 9:49 AM Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
> > diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
> > index fdabf40a83c8..9a8bd4bc8549 100644
> > --- a/arch/arm64/mm/proc.S
> > +++ b/arch/arm64/mm/proc.S
> > @@ -73,6 +73,9 @@ alternative_endif
> > stp x8, x9, [x0, #48]
> > stp x10, x11, [x0, #64]
> > stp x12, x13, [x0, #80]
> > +#ifdef CONFIG_SHADOW_CALL_STACK
> > + stp x18, xzr, [x0, #96]
>
> Could this be a str/ldr of just x18 rather than stp/ldp of x18 +
> garbage? Maybe there's no real cost difference, or some kind of
> alignment invariant?
Sure, this can be changed to str/ldr. I don't think there's a
noticeable difference in cost.
Sami
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