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

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Message-ID: <20200807131429.GB664450@kroah.com>
Date:   Fri, 7 Aug 2020 15:14:29 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Will Deacon <will.deacon@....com>, Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, stable@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        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, Aug 06, 2020 at 01:00:54PM -0700, Florian Fainelli wrote:
> 
> 
> On 7/20/2020 11:26 AM, Florian Fainelli wrote:
> > On 7/20/20 6:04 AM, Greg KH wrote:
> >> 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?
> > 
> > Sure, send you candidates for 4.14 and 4.19.
> 
> Greg, did you have a chance to queue those changes for 4.9, 4.14 and 4.19?
> 
> https://lore.kernel.org/linux-arm-kernel/20200720182538.13304-1-f.fainelli@gmail.com/
> https://lore.kernel.org/linux-arm-kernel/20200720182937.14099-1-f.fainelli@gmail.com/
> https://lore.kernel.org/linux-arm-kernel/20200709195034.15185-1-f.fainelli@gmail.com/

Nope, I was waiting for Will's "ack" for these.

thanks,

greg k-h