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

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Message-ID: <fb3be972-106e-e171-1c2f-6df20ce186d6@gmail.com>
Date:   Fri, 7 Aug 2020 11:17:23 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>,
        Will Deacon <will.deacon@....com>,
        Will Deacon <will@...nel.org>
Cc:     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 8/7/2020 6:14 AM, Greg KH wrote:
> 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.

OK, Will, can you review those? Thanks
-- 
Florian