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Wed, 07 Apr 2021 12:56:19 -0700 (PDT) Received: from [192.168.1.11] ([71.212.131.83]) by smtp.gmail.com with ESMTPSA id c9sm20725420pfl.169.2021.04.07.12.56.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 07 Apr 2021 12:56:18 -0700 (PDT) Subject: Re: [PATCH v4 03/12] target/arm: Fix mte_checkN To: =?UTF-8?Q?Alex_Benn=c3=a9e?= References: <20210406174031.64299-1-richard.henderson@linaro.org> <20210406174031.64299-4-richard.henderson@linaro.org> <877dleuds3.fsf@linaro.org> From: Richard Henderson Message-ID: Date: Wed, 7 Apr 2021 12:56:17 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <877dleuds3.fsf@linaro.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2607:f8b0:4864:20::1033; envelope-from=richard.henderson@linaro.org; helo=mail-pj1-x1033.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: 1921948@bugs.launchpad.net, qemu-arm@nongnu.org, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 4/7/21 11:39 AM, Alex Bennée wrote: > > Richard Henderson writes: > >> We were incorrectly assuming that only the first byte of an MTE access >> is checked against the tags. But per the ARM, unaligned accesses are >> pre-decomposed into single-byte accesses. So by the time we reach the >> actual MTE check in the ARM pseudocode, all accesses are aligned. >> >> Therefore, the first failure is always either the first byte of the >> access, or the first byte of the granule. >> >> In addition, some of the arithmetic is off for last-first -> count. >> This does not become directly visible until a later patch that passes >> single bytes into this function, so ptr == ptr_last. >> >> Buglink: https://bugs.launchpad.net/bugs/1921948 > > Minor note: you can Cc: Bug 1921948 <1921948@bugs.launchpad.net> to > automatically copy patches to the appropriate bugs which is useful if > you don't have the Cc for the reporter. > > Anyway I'm trying to get the kasas unit tests running as a way of > testing this (and maybe expanding with a version of Andrey's test). I > suspect this may be a PEBCAC issue but I built an MTE enabled kernel > with: > > CONFIG_HAVE_ARCH_KASAN=y > CONFIG_HAVE_ARCH_KASAN_SW_TAGS=y > CONFIG_HAVE_ARCH_KASAN_HW_TAGS=y > CONFIG_CC_HAS_KASAN_GENERIC=y > CONFIG_KASAN=y > # CONFIG_KASAN_GENERIC is not set > CONFIG_KASAN_HW_TAGS=y > CONFIG_KASAN_STACK=1 > CONFIG_KASAN_KUNIT_TEST=m > CONFIG_TEST_KASAN_MODULE=m I built it all in: CONFIG_HAVE_ARCH_KASAN=y CONFIG_HAVE_ARCH_KASAN_SW_TAGS=y CONFIG_HAVE_ARCH_KASAN_HW_TAGS=y CONFIG_CC_HAS_KASAN_GENERIC=y CONFIG_KASAN=y # CONFIG_KASAN_GENERIC is not set CONFIG_KASAN_HW_TAGS=y CONFIG_KASAN_KUNIT_TEST=y Then I just boot the raw kernel (no filesystem or anything): ./qemu-system-aarch64 -M virt,mte=on -cpu max -nographic \ -kernel ~/linux/bld-aa/arch/arm64/boot/Image There's a ton of output, but at the end I see [ 11.901185] ok 48 - match_all_mem_tag [ 11.901422] ok 1 - kasan just before the "VFS: Cannot open root device" panic. Which has done all we wanted, so, yay. r~