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

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Date:   Tue, 26 Jan 2021 12:07:16 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     Lecopzer Chen <lecopzer.chen@...iatek.com>,
        akpm@...ux-foundation.org, 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, tglx@...utronix.de
Subject: Re: [PATCH] ARM: mm: harden branch predictor before opening
 interrupts during fault

On 2021-01-26 10:59:32 [+0000], Russell King - ARM Linux admin wrote:
> 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.

My memory is that I never got a reply which I understood.
Let me try again this week with the information above.

Sebastian