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Fri, 26 Jan 2024 08:57:45 -0800 (PST) MIME-Version: 1.0 References: <20240124173134.1165747-1-glider@google.com> <20240125173448.e866d84cda146145cbc67c93@linux-foundation.org> In-Reply-To: <20240125173448.e866d84cda146145cbc67c93@linux-foundation.org> From: Alexander Potapenko Date: Fri, 26 Jan 2024 17:57:04 +0100 Message-ID: Subject: Re: [PATCH v2] mm: kmsan: remove runtime checks from kmsan_unpoison_memory() To: Andrew Morton Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, kasan-dev@googlegroups.com, Marco Elver , Dmitry Vyukov , Ilya Leoshkevich , Nicholas Miehlbradt Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 8C21580020 X-Stat-Signature: knpfspk4byjp48htnrxx8n15sm5tex7p X-HE-Tag: 1706288266-774971 X-HE-Meta: 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 L9zmkDwF uDo5IfUw0RlEnoTdKeWq4ytLWBibbxpWBRSjUfas1fEkLRUWAVdJybucQ1bNWcN0yTZVnG6EHVQMOm1Vb1zBfgEhpCPV1D29HhofEs/oqmv3VP8Cd9FBCzGXs1qn++jpurgyuWZRb0m37cIFpgnULIKZhdZBGV6DvZjHQZFjib3uYAzA9wr8+HUWS9GdkIdV2aWXKFPhaPPgdkQYrb0ILG1PqIU9tw1Nj9XIdL1Jb4chRt/vyjkbC+dbHiODA+VKGfSpfvB8WSxfqmtkH0wpG5ZRj4yToGnfjQf4nT+5lwVSo/yiw2RYglXa/EgEl5gCty+F7zfJlO7oyDN5LdSFP/CkCIrd689wLsKwK X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, 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, Jan 26, 2024 at 2:34=E2=80=AFAM Andrew Morton wrote: > > On Wed, 24 Jan 2024 18:31:34 +0100 Alexander Potapenko wrote: > > > Similarly to what's been done in commit ff444efbbb9be ("kmsan: allow > > I make that 85716a80c16d. > > > using __msan_instrument_asm_store() inside runtime"), it should be safe > > to call kmsan_unpoison_memory() from within the runtime, as it does not > > allocate memory or take locks. Remove the redundant runtime checks. > > > > This should fix false positives seen with CONFIG_DEBUG_LIST=3Dy when > > the non-instrumented lib/stackdepot.c failed to unpoison the memory > > chunks later checked by the instrumented lib/list_debug.c > > > > Also replace the implementation of kmsan_unpoison_entry_regs() with > > a call to kmsan_unpoison_memory(). > > > > "false positives" sound unpleasant. Should this fix be backported into > earlier kernels? And can we identify a suitable Fixes: target? > Surprisingly, I haven't seen these false reports before, but the bug has been there since KMSAN's early downstream days (at the time we might have needed to have those checks). So it should probably be: Fixes: f80be4571b19b9 ("kmsan: add KMSAN runtime core")