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[192.33.36.4]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a626cc8e585sm621718666b.184.2024.05.28.08.45.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 28 May 2024 08:45:13 -0700 (PDT) Date: Tue, 28 May 2024 17:45:12 +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 Subject: Re: [PATCH] kmsan: introduce test_unpoison_memory() Message-ID: References: <20240524232804.1984355-1-bjohannesmeyer@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: BA1AAA000B X-Stat-Signature: wgpz3faznq9xaw3x811jt5d3beone4jp X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1716911115-92426 X-HE-Meta: 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 CoboH/ud DoibsdHh/XVUrdxPNMlJTPzK73PZPexa6kC3IyvD4ObqL9rX2fq7Bz8/rdmLRaQI0GMGHCVN34MKYNOdBFghvUcnrNWT2KSakjkKOiS/zEgEdtj+8OdQLzs73GDaDcn0fN6AVoJRS7KuXMT2PSL/qYve295bpAy2OjdtLSH+ool9JW+HTD6XNIu7XJHUpRMVz5OdTIRdRG9AYdISqZ2I+eUe1oPcbBxtOSrINQpkWrS+bOWHZZHCHwzL1nPXMX5Jwr0OzIB3p6HS51V1Vo7d/DrELWyVOaD1F4HxwwZr+JvBoKyvXLZzvhwEvuGtNnbehcEw75vucK2HTI+w1THSGLoT8pZ39WdZM4wErY7GZ4VV00yPws29ZI54ktSHD3HU1uXVbaQH5UAx8CdD0UC/RryaWI/5R5mOZpnF5wYYD4UdHYouTUKHxPmcM+cm4gjTPQgk3Fh96DQkJqwaVfR6GX1gErVwDh1V/G9GI X-Bogosity: Ham, tests=bogofilter, spamicity=0.097666, 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 Tue, May 28, 2024 at 12:20:15PM +0200, Alexander Potapenko wrote: > You are right with your analysis. > KMSAN stores a single origin for every aligned four-byte granule of > memory, so we lose some information when more than one uninitialized > value is combined in that granule. > When writing an uninitialized value to memory, a viable strategy is to > always update the origin. But if we partially initialize the granule > with a store, it is better to preserve that granule's origin to > prevent false negatives, so we need to check the resulting shadow slot > before updating the origin. > This is what the compiler instrumentation does, so > kmsan_internal_set_shadow_origin() should behave in the same way. > I found a similar bug in kmsan_internal_memmove_metadata() last year, > but missed this one. I appreciate the explanation. Makes sense. > I am going to send a patch fixing this along with your test (with an > updated description), if you don't object. Yes, that's fine. Thank you. -Brian