linux-kernel - Re: [PATCH] ARM: mm: harden branch predictor before opening interrupts during fault

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Message-ID: <20210126105932.GG1551@shell.armlinux.org.uk>
Date:   Tue, 26 Jan 2021 10:59:32 +0000
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Lecopzer Chen <lecopzer.chen@...iatek.com>
Cc:     akpm@...ux-foundation.org, bigeasy@...utronix.de,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        marc.zyngier@....com, peterx@...hat.com, rppt@...nel.org,
        walken@...gle.com, yj.chiang@...iatek.com
Subject: Re: [PATCH] ARM: mm: harden branch predictor before opening
 interrupts during fault

On Tue, Jan 26, 2021 at 05:17:08PM +0800, Lecopzer Chen wrote:
> Hi all,
> 
> I don't see any fix for this issue now(maybe I missed it..?),
> could we fix this if there is better solution?
> This issue exists almost two years.

I don't think anyone provided an acceptable patch.

The first patch moved the hardening out of the translation/section
fault handling. Since the kernel is mapped with sections, these
are above TASK_SIZE, and the whole point of the branch prediction
hardening is to prevent the prediction in the kernel being exploited,
missing the hardening effectively makes the mitigation useless.

The discussion in February 2019 never concluded from what I can see.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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