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Mon, 24 Aug 2020 09:42:54 -0700 (PDT) Subject: Re: [PATCH stable v4.9 v2] arm64: entry: Place an SB sequence following an ERET instruction To: Will Deacon References: <20200709195034.15185-1-f.fainelli@gmail.com> <20200720130411.GB494210@kroah.com> <9c29080e-8b3a-571c-3296-e0487fa473fa@gmail.com> <20200807131429.GB664450@kroah.com> <20200821160316.GE21517@willie-the-truck> <7480435b-355d-b9f7-3a42-b72a9c4b6f63@gmail.com> <20200824163208.GA25316@willie-the-truck> From: Florian Fainelli Message-ID: Date: Mon, 24 Aug 2020 09:42:53 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Firefox/78.0 Thunderbird/78.1.1 MIME-Version: 1.0 In-Reply-To: <20200824163208.GA25316@willie-the-truck> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200824_124300_184725_EA79D855 X-CRM114-Status: GOOD ( 27.82 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Nick Desaulniers , Andrew Jones , Catalin Marinas , Fangrui Song , Suzuki K Poulose , Marc Zyngier , Will Deacon , open list , stable@vger.kernel.org, "open list:KERNEL VIRTUAL MACHINE FOR ARM64 \(KVM/arm64\)" , Mark Brown , James Morse , Julien Thierry , Sami Tolvanen , Greg KH , Kristina Martsenko , Ard Biesheuvel , linux-arm-kernel@lists.infradead.org Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 8/24/2020 9:32 AM, Will Deacon wrote: > Hi Florian, > > On Fri, Aug 21, 2020 at 10:16:23AM -0700, Florian Fainelli wrote: >> On 8/21/20 9:03 AM, Will Deacon wrote: >>> On Fri, Aug 07, 2020 at 03:14:29PM +0200, Greg KH wrote: >>>> On Thu, Aug 06, 2020 at 01:00:54PM -0700, Florian Fainelli wrote: >>>>> 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. >>> >>> This patch doesn't even build for me (the 'sb' macro is not defined in 4.9), >>> and I really wonder why we bother backporting it at all. Nobody's ever shown >>> it to be a problem in practice, and it's clear that this is just being >>> submitted to tick a box rather than anything else (otherwise it would build, >>> right?). >> >> Doh, I completely missed submitting the patch this depended on that's >> why I did not notice the build failure locally, sorry about that, what a >> shame. >> >> Would not be the same "tick a box" argument be used against your >> original submission then? Sure, I have not been able to demonstrate in >> real life this was a problem, however the same can be said about a lot >> security related fixes. > > Sort of, although I wrote the original patch because it was dead easy to do > and saved having to think too much about the problem, whereas the complexity > of backporting largerly diminishes that imo. > >> What if it becomes exploitable in the future, would not it be nice to >> have it in a 6 year LTS kernel? > > Even if people are stuck on an old LTS, they should still be taking the > regular updates for it, and we would obviously need to backport the fix if > it turned out to be exploitable (and hey, we could even test it then!). > >>> So I'm not going to Ack any of them. As with a lot of this side-channel >>> stuff the cure is far worse than the disease. >> Assuming that my v3 does build correctly, which it will, would you be >> keen on changing your position? > > Note that I'm not trying to block this patch from going in, I'm just saying > that I'm not supportive of it. Perhaps somebody from Arm can review it if > they think it's worth the effort. How about I submit the actual full series (two patches) and we take the discussion from there? Thanks for responding! -- Florian _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel