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[2003:cb:c71b:7900:8752:fae3:f9c9:a07e]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-39c301ba2dfsm5197359f8f.60.2025.04.04.13.18.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 04 Apr 2025 13:18:11 -0700 (PDT) Message-ID: Date: Fri, 4 Apr 2025 22:18:09 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 0/4] support FEAT_MTE_STORE_ONLY feature To: Yeoreum Yun Cc: catalin.marinas@arm.com, will@kernel.org, broonie@kernel.org, anshuman.khandual@arm.com, joey.gouly@arm.com, maz@kernel.org, oliver.upton@linux.dev, frederic@kernel.org, james.morse@arm.com, hardevsinh.palaniya@siliconsignals.io, shameerali.kolothum.thodi@huawei.com, huangxiaojia2@huawei.com, mark.rutland@arm.com, samuel.holland@sifive.com, palmer@rivosinc.com, charlie@rivosinc.com, thiago.bauermann@linaro.org, bgray@linux.ibm.com, tglx@linutronix.de, puranjay@kernel.org, yang@os.amperecomputing.com, mbenes@suse.cz, joel.granados@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, nd@arm.com References: <20250403174701.74312-1-yeoreum.yun@arm.com> <1618bf36-7f7a-4d32-a6a6-242323007d67@redhat.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 04.04.25 21:33, Yeoreum Yun wrote: > Hi David. > >> On 03.04.25 19:46, Yeoreum Yun wrote: >>> The FEAT_MTE_STORE_ONLY feature provides support for >>> tag check for store operation only. read operation is considered >>> as unchecked operation so it doesn't raise tag check fault. >> >> Can you add/share more details of what the implications are, how it would be >> used, who would set it, etc. >> >> Just from staring at this short paragraph leaves me rather clueless. >> > > Sorry for my bad. > > ARMv8.5 based processors introduce the Memory Tagging Extension (MTE) feature. > MTE is built on top of the ARMv8.0 virtual address tagging TBI > (Top Byte Ignore) feature and allows software to access a 4-bit > allocation tag for each 16-byte granule in the physical address space. > A logical tag is derived from bits 59-56 of the virtual > address used for the memory access. A CPU with MTE enabled will compare > the logical tag against the allocation tag and potentially raise an > tag check fault on mismatch, subject to system registers configuration. > > Since ARMv8.9, FEAT_MTE_STORE_ONLY can be used to restrict raise of tag > check fault on store operation only. Oh, so other operations (read/fetch) will not check the tag. > For this, application can use PR_MTE_STORE_ONLY flag > when it sets the MTE setting with prctl(). > > This would be useful for debugging purpose > i.e) finding memory courruption point, use-after-free and etc. So what's the benefit of this relaxation? I assume it's faster because less memory access has to perform tag checks, and the issues you mention here can still be mostly caught (not all cases of use-after-free, but at least the destructive ones). -- Cheers, David / dhildenb