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Mon, 11 Feb 2019 03:53:01 -0800 (PST) Received: from [10.1.196.62] (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E7B8C3F557; Mon, 11 Feb 2019 03:52:59 -0800 (PST) Subject: Re: [PATCH] arm64/io: Don't use WZR in writel To: Will Deacon , AngeloGioacchino Del Regno Cc: Jens Axboe , Catalin Marinas , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-arm-msm@vger.kernel.org References: <68b71c15f32341468a868f6418e4fcb375bc49ba.camel@gmail.com> <20190211105755.GB30880@fuggles.cambridge.arm.com> From: Marc Zyngier Openpgp: preference=signencrypt Autocrypt: addr=marc.zyngier@arm.com; prefer-encrypt=mutual; keydata= mQINBE6Jf0UBEADLCxpix34Ch3kQKA9SNlVQroj9aHAEzzl0+V8jrvT9a9GkK+FjBOIQz4KE g+3p+lqgJH4NfwPm9H5I5e3wa+Scz9wAqWLTT772Rqb6hf6kx0kKd0P2jGv79qXSmwru28vJ t9NNsmIhEYwS5eTfCbsZZDCnR31J6qxozsDHpCGLHlYym/VbC199Uq/pN5gH+5JHZyhyZiNW ozUCjMqC4eNW42nYVKZQfbj/k4W9xFfudFaFEhAf/Vb1r6F05eBP1uopuzNkAN7vqS8XcgQH qXI357YC4ToCbmqLue4HK9+2mtf7MTdHZYGZ939OfTlOGuxFW+bhtPQzsHiW7eNe0ew0+LaL 3wdNzT5abPBscqXWVGsZWCAzBmrZato+Pd2bSCDPLInZV0j+rjt7MWiSxEAEowue3IcZA++7 ifTDIscQdpeKT8hcL+9eHLgoSDH62SlubO/y8bB1hV8JjLW/jQpLnae0oz25h39ij4ijcp8N t5slf5DNRi1NLz5+iaaLg4gaM3ywVK2VEKdBTg+JTg3dfrb3DH7ctTQquyKun9IVY8AsxMc6 lxl4HxrpLX7HgF10685GG5fFla7R1RUnW5svgQhz6YVU33yJjk5lIIrrxKI/wLlhn066mtu1 DoD9TEAjwOmpa6ofV6rHeBPehUwMZEsLqlKfLsl0PpsJwov8TQARAQABtCNNYXJjIFp5bmdp ZXIgPG1hcmMuenluZ2llckBhcm0uY29tPokCOwQTAQIAJQIbAwYLCQgHAwIGFQgCCQoLBBYC AwECHgECF4AFAk6NvYYCGQEACgkQI9DQutE9ekObww/+NcUATWXOcnoPflpYG43GZ0XjQLng LQFjBZL+CJV5+1XMDfz4ATH37cR+8gMO1UwmWPv5tOMKLHhw6uLxGG4upPAm0qxjRA/SE3LC 22kBjWiSMrkQgv5FDcwdhAcj8A+gKgcXBeyXsGBXLjo5UQOGvPTQXcqNXB9A3ZZN9vS6QUYN TXFjnUnzCJd+PVI/4jORz9EUVw1q/+kZgmA8/GhfPH3xNetTGLyJCJcQ86acom2liLZZX4+1 6Hda2x3hxpoQo7pTu+XA2YC4XyUstNDYIsE4F4NVHGi88a3N8yWE+Z7cBI2HjGvpfNxZnmKX 6bws6RQ4LHDPhy0yzWFowJXGTqM/e79c1UeqOVxKGFF3VhJJu1nMlh+5hnW4glXOoy/WmDEM UMbl9KbJUfo+GgIQGMp8mwgW0vK4HrSmevlDeMcrLdfbbFbcZLNeFFBn6KqxFZaTd+LpylIH bOPN6fy1Dxf7UZscogYw5Pt0JscgpciuO3DAZo3eXz6ffj2NrWchnbj+SpPBiH4srfFmHY+Y LBemIIOmSqIsjoSRjNEZeEObkshDVG5NncJzbAQY+V3Q3yo9og/8ZiaulVWDbcpKyUpzt7pv cdnY3baDE8ate/cymFP5jGJK++QCeA6u6JzBp7HnKbngqWa6g8qDSjPXBPCLmmRWbc5j0lvA 6ilrF8m5Ag0ETol/RQEQAM/2pdLYCWmf3rtIiP8Wj5NwyjSL6/UrChXtoX9wlY8a4h3EX6E3 64snIJVMLbyr4bwdmPKULlny7T/R8dx/mCOWu/DztrVNQiXWOTKJnd/2iQblBT+W5W8ep/nS w3qUIckKwKdplQtzSKeE+PJ+GMS+DoNDDkcrVjUnsoCEr0aK3cO6g5hLGu8IBbC1CJYSpple VVb/sADnWF3SfUvJ/l4K8Uk4B4+X90KpA7U9MhvDTCy5mJGaTsFqDLpnqp/yqaT2P7kyMG2E w+eqtVIqwwweZA0S+tuqput5xdNAcsj2PugVx9tlw/LJo39nh8NrMxAhv5aQ+JJ2I8UTiHLX QvoC0Yc/jZX/JRB5r4x4IhK34Mv5TiH/gFfZbwxd287Y1jOaD9lhnke1SX5MXF7eCT3cgyB+ hgSu42w+2xYl3+rzIhQqxXhaP232t/b3ilJO00ZZ19d4KICGcakeiL6ZBtD8TrtkRiewI3v0 o8rUBWtjcDRgg3tWx/PcJvZnw1twbmRdaNvsvnlapD2Y9Js3woRLIjSAGOijwzFXSJyC2HU1 AAuR9uo4/QkeIrQVHIxP7TJZdJ9sGEWdeGPzzPlKLHwIX2HzfbdtPejPSXm5LJ026qdtJHgz BAb3NygZG6BH6EC1NPDQ6O53EXorXS1tsSAgp5ZDSFEBklpRVT3E0NrDABEBAAGJAh8EGAEC AAkFAk6Jf0UCGwwACgkQI9DQutE9ekMLBQ//U+Mt9DtFpzMCIHFPE9nNlsCm75j22lNiw6mX mx3cUA3pl+uRGQr/zQC5inQNtjFUmwGkHqrAw+SmG5gsgnM4pSdYvraWaCWOZCQCx1lpaCOl MotrNcwMJTJLQGc4BjJyOeSH59HQDitKfKMu/yjRhzT8CXhys6R0kYMrEN0tbe1cFOJkxSbV 0GgRTDF4PKyLT+RncoKxQe8lGxuk5614aRpBQa0LPafkirwqkUtxsPnarkPUEfkBlnIhAR8L kmneYLu0AvbWjfJCUH7qfpyS/FRrQCoBq9QIEcf2v1f0AIpA27f9KCEv5MZSHXGCdNcbjKw1 39YxYZhmXaHFKDSZIC29YhQJeXWlfDEDq6nIhvurZy3mSh2OMQgaIoFexPCsBBOclH8QUtMk a3jW/qYyrV+qUq9Wf3SKPrXf7B3xB332jFCETbyZQXqmowV+2b3rJFRWn5hK5B+xwvuxKyGq qDOGjof2dKl2zBIxbFgOclV7wqCVkhxSJi/QaOj2zBqSNPXga5DWtX3ekRnJLa1+ijXxmdjz hApihi08gwvP5G9fNGKQyRETePEtEAWt0b7dOqMzYBYGRVr7uS4uT6WP7fzOwAJC4lU7ZYWZ yVshCa0IvTtp1085RtT3qhh9mobkcZ+7cQOY+Tx2RGXS9WeOh2jZjdoWUv6CevXNQyOUXMM= Organization: ARM Ltd Message-ID: <38d8965a-cd41-17cf-1b95-8dd58c079be4@arm.com> Date: Mon, 11 Feb 2019 11:52:52 +0000 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <20190211105755.GB30880@fuggles.cambridge.arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/02/2019 10:57, Will Deacon wrote: > On Sat, Feb 09, 2019 at 07:34:53PM +0100, AngeloGioacchino Del Regno wrote: >> From 33fb6d036de273bb71ac1c67d7a91b7a5148e659 Mon Sep 17 00:00:00 2001 >> From: "Angelo G. Del Regno" >> Date: Sat, 9 Feb 2019 18:56:46 +0100 >> Subject: [PATCH] arm64/io: Don't use WZR in writel >> >> This is a partial revert of commit ee5e41b5f21a >> ("arm64/io: Allow I/O writes to use {W,X}ZR") >> >> When we try to use the zero register directly on some SoCs, >> their security will make them freeze due to a firmware bug.>> This behavior is seen with the arm-smmu driver freezing on >> TLBI and TLBSYNC on MSM8996, MSM8998, SDM630, SDM660. This looks similar to the issue these SoCs have with GICv3, worked around in 9c8114c20d18. > Hmm, this sounds very fragile. I hope they're not trapping and emulating > MMIO accesses and treating the zero register as the stack pointer... I bet this is the case. The same bug was there in both KVM and Xen. The only difference is that we fixed it back in December 2015 (at least for KVM), while some of these SoCs were announced in 2017, and are still shipping. Great stuff. > > Wouldn't this also be triggerable from userspace by mmap()ing either > /dev/mem or e.g. a PCI bar via sysfs? > >> Allocating a temporary register to store the zero for the >> write actually solves the issue on these SoCs. > > I don't think this catches all MMIO accesses, so I think we need to > understand more about the actual issue here. For example, is it only the > SMMU that causes this problem? Also, any workaround should be specific to > the broken SoCs. Also, nothing would prevent a compiler from generating these accesses. M. Jazz is not dead. It just smells funny...