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Message-ID: <CAKv+Gu9DD12BPV_jNv9Hjw4oSiZvtdiVVjB-B8WLXCoPL4CA9Q@mail.gmail.com>
Date: Thu, 7 Nov 2019 11:51:38 +0100
From: Ard Biesheuvel <ard.biesheuvel@...aro.org>
To: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc: Sami Tolvanen <samitolvanen@...gle.com>, Will Deacon <will@...nel.org>,
Catalin Marinas <catalin.marinas@....com>, Steven Rostedt <rostedt@...dmis.org>,
Masami Hiramatsu <mhiramat@...nel.org>, Dave Martin <Dave.Martin@....com>,
Kees Cook <keescook@...omium.org>, Laura Abbott <labbott@...hat.com>,
Mark Rutland <mark.rutland@....com>, Marc Zyngier <maz@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>, Jann Horn <jannh@...gle.com>,
Masahiro Yamada <yamada.masahiro@...ionext.com>,
clang-built-linux <clang-built-linux@...glegroups.com>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Linux ARM <linux-arm-kernel@...ts.infradead.org>,
linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 11/14] arm64: efi: restore x18 if it was corrupted
On Wed, 6 Nov 2019 at 05:46, Miguel Ojeda
<miguel.ojeda.sandonis@...il.com> wrote:
>
> On Wed, Nov 6, 2019 at 12:56 AM Sami Tolvanen <samitolvanen@...gle.com> wrote:
> >
> > If we detect a corrupted x18 and SCS is enabled, restore the register
> > before jumping back to instrumented code. This is safe, because the
> > wrapper is called with preemption disabled and a separate shadow stack
> > is used for interrupt handling.
>
> In case you do v6: I think putting the explanation about why this is
> safe in the existing comment would be best given it is justifying a
> subtlety of the code rather than the change itself. Ard?
>
Agreed, but only if you have to respin for other reasons.
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