linux-kernel - Re: [PATCH stable 4.9] arm64: entry: Place an SB sequence following an ERET instruction

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Message-ID: <2bcebe48-1218-403a-798c-da30d678fdd6@gmail.com>
Date:   Tue, 23 Jun 2020 11:46:37 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     linux-arm-kernel@...ts.infradead.org, will@...nel.org,
        Catalin Marinas <catalin.marinas@....com>
Cc:     stable@...r.kernel.org, Will Deacon <will.deacon@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Christoffer Dall <christoffer.dall@...aro.org>,
        Marc Zyngier <marc.zyngier@....com>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:KERNEL VIRTUAL MACHINE (KVM)" <kvm@...r.kernel.org>,
        "open list:KERNEL VIRTUAL MACHINE FOR ARM64 (KVM/arm64)" 
        <kvmarm@...ts.cs.columbia.edu>
Subject: Re: [PATCH stable 4.9] arm64: entry: Place an SB sequence following
 an ERET instruction

On 6/11/20 9:42 PM, Florian Fainelli wrote:
> From: Will Deacon <will.deacon@....com>
> 
> commit 679db70801da9fda91d26caf13bf5b5ccc74e8e8 upstream
> 
> Some CPUs can speculate past an ERET instruction and potentially perform
> speculative accesses to memory before processing the exception return.
> Since the register state is often controlled by a lower privilege level
> at the point of an ERET, this could potentially be used as part of a
> side-channel attack.
> 
> This patch emits an SB sequence after each ERET so that speculation is
> held up on exception return.
> 
> Signed-off-by: Will Deacon <will.deacon@....com>
> [florian: Adjust hyp-entry.S to account for the label]
> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
> ---
> Will,
> 
> Can you confirm that for 4.9 these are the only places that require
> patching? Thank you!

Hi Will, Catalin,

Does this look good to you for a 4.9 backport? I would like to see this
included at some point since this pertains to CVE-2020-13844.

Thanks!
-- 
Florian