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Fri, 21 Aug 2020 12:03:23 -0400 (EDT) Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by mm01.cs.columbia.edu (Postfix) with ESMTPS id B04664C540 for ; Fri, 21 Aug 2020 12:03:23 -0400 (EDT) Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 925FE207BB; Fri, 21 Aug 2020 16:03:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598025802; bh=s7k7WVoMuW3YOq62B9s+ZiSRUJCQ9bWnTQTRHx+L47U=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=rUqMkCwqrjDQLVFDCML+UPPcErgSGgrMWu/c98cem9NQGN6T+mOGaXb0ioOHagXdG 5y0iD5+V2N72brnN7NCXB43WQZhiDtmc9Me9xJT3z6dHpaKZXFDH8Y0r3F3qw/daXe xtT46gOoAtOT09c9Q1JHr9geLPFmMtNd8KKu0lt0= Date: Fri, 21 Aug 2020 17:03:16 +0100 From: Will Deacon To: Greg KH Subject: Re: [PATCH stable v4.9 v2] arm64: entry: Place an SB sequence following an ERET instruction Message-ID: <20200821160316.GE21517@willie-the-truck> References: <20200709195034.15185-1-f.fainelli@gmail.com> <20200720130411.GB494210@kroah.com> <9c29080e-8b3a-571c-3296-e0487fa473fa@gmail.com> <20200807131429.GB664450@kroah.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200807131429.GB664450@kroah.com> User-Agent: Mutt/1.10.1 (2018-07-13) Cc: Nick Desaulniers , Florian Fainelli , Fangrui Song , Catalin Marinas , Will Deacon , open list , stable@vger.kernel.org, "open list:KERNEL VIRTUAL MACHINE FOR ARM64 \(KVM/arm64\)" , Mark Brown , Sami Tolvanen , Marc Zyngier , Kristina Martsenko , Ard Biesheuvel , linux-arm-kernel@lists.infradead.org X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu 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: > > > > > > 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 > > >>> > > >>> 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 > > >>> [florian: Adjust hyp-entry.S to account for the label > > >>> added change to hyp/entry.S] > > >>> Signed-off-by: Florian Fainelli > > >>> --- > > >>> 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. 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?). 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. Will _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm