linux-kernel - Re: [PATCH v2 16/18] arm64: crypto: disable LTO for aes-ce-cipher.c

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Message-ID: <20171120210143.GD89108@samitolvanen.mtv.corp.google.com>
Date:   Mon, 20 Nov 2017 13:01:43 -0800
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Mark Rutland <mark.rutland@....com>,
        Alex Matveev <alxmtvv@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Greg Hackmann <ghackmann@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        linux-kbuild@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Maxim Kuvyrkov <maxim.kuvyrkov@...aro.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Yury Norov <ynorov@...iumnetworks.com>,
        Matthias Kaehlcke <mka@...omium.org>
Subject: Re: [PATCH v2 16/18] arm64: crypto: disable LTO for aes-ce-cipher.c

On Mon, Nov 20, 2017 at 03:25:31PM +0000, Ard Biesheuvel wrote:
> However, under LTO this all changes, and it is no longer guaranteed
> that the NEON registers are only touched between the kernel mode
> neon begin/end calls.

LTO operates on LLVM IR, so disabling LTO for this file should make
sure there won't be any unsafe optimizations. Are there other places
in the kernel that might have this issue?

> So the correct way to fix this would be to move the asm into its own
> .S file, and call it from between the kernel_mode_neon_begin/end
> calls. That should also fix your compat issue.

Sure, that would also work.
 
Sami