linux-kernel - Re: [PATCH stable v4.9 v2] arm64: entry: Place an SB sequence following an ERET instruction

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Message-ID: <20200720130411.GB494210@kroah.com>
Date:   Mon, 20 Jul 2020 15:04:11 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     linux-arm-kernel@...ts.infradead.org, stable@...r.kernel.org,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Mark Rutland <mark.rutland@....com>,
        Mark Brown <broonie@...nel.org>,
        Kristina Martsenko <kristina.martsenko@....com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Andrew Jones <drjones@...hat.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Fangrui Song <maskray@...gle.com>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:KERNEL VIRTUAL MACHINE FOR ARM64 (KVM/arm64)" 
        <kvmarm@...ts.cs.columbia.edu>
Subject: Re: [PATCH stable v4.9 v2] arm64: entry: Place an SB sequence
 following an ERET instruction

On Thu, Jul 09, 2020 at 12:50:23PM -0700, 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
>  added change to hyp/entry.S]
> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
> ---
> Changes in v2:
> 
> - added missing hunk in hyp/entry.S per Will's feedback

What about 4.19.y and 4.14.y trees?  I can't take something for 4.9.y
and then have a regression if someone moves to a newer release, right?

thanks,

greg k-h