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[192.33.36.4]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-57872da9dfbsm23821a12.2.2024.05.24.15.35.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 24 May 2024 15:35:54 -0700 (PDT) Date: Sat, 25 May 2024 00:35:52 +0200 From: Brian Johannesmeyer To: Alexander Potapenko Cc: Marco Elver , Dmitry Vyukov , Andrew Morton , kasan-dev@googlegroups.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H . Peter Anvin" Subject: Re: [PATCH] x86: kmsan: Fix hook for unaligned accesses Message-ID: References: <20240523215029.4160518-1-bjohannesmeyer@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 631684000D X-Stat-Signature: if3fwjzkxq1uhdi3hypbecgkzwqxrtkp X-Rspam-User: X-HE-Tag: 1716590156-316192 X-HE-Meta: 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 +tWjZBDY tHB/ogrjWf+VtFJJbKMMc9DeRv0/6Hi7QAiUR47LkrMXxF/0TgmjJkW0dZ0T0UXBn8mL9KDabdBRMZRtoIN/S78hj8FOChVLrmjmFvP5i2WktHCLwiu1MUc3LDynVRBL4B3yBvl9NOKCzeFt3RpMLC8jXVV4YMNqnxXuNeeOiatcNamzSS8YSNRLiPcBeUJiYlM3pCA2G3kWIkCDBK51SeStYsdnnbxDchqycqIEqo6IqYLLKHRG6UKYrK9f46BXBpEXKoH0aJNckaMHgDalGIKGh6jW1E5YGIfzyqFq71OEyYcKH8DevlPlhkMbBxTRYr7HL8CljgHliGHgIr6My+g6VkLUvaRkrMbf1GdAaLYl1Nq5H5M5mRWuOL+sThAumCcfcesjzTIPEKdbsRMAOFt0U4f/X8PTZcXMAh/w+X2URVLyjWRFIBdFYBaI1/QSPFXco8XmQ5RvH/ds= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, May 24, 2024 at 10:28:05AM +0200, Alexander Potapenko wrote: > Nice catch! Does it fix any known bugs? Not that I know of. Based on my cursory testing, it seems that string_memcpy_fromio() is rarely called with an unaligned `from`, so this is a bit of an edge case. On that note: I tried creating a unit test for this, to verify that an unaligned memcpy_fromio() would yield uninitialized data without the patch, and would yield initialized data with the patch. However, what I found is that kmsan_unpoison_memory() seems to always unpoison an entire 4-byte word, even if called with a `size` of less than 4. However, this issue is somewhat unrelated to the patch at hand, so I'll create a separate patch to demonstrate what I mean. Thanks, Brian