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bh=6FV8fZUyx9UIT2B/NjKf+b+AZwI+qTujj+rXUvmQIgU=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=CKExzjS4d7IXI/NiqujPvAen6pYz1n0k0ul13G+wziuLYNkU7pRc3T9LK6UK2CMpL yZF0E1NiC6sP+7JbDcyGUONH5NPH5y3ZfC+W9+ERe/aLGGevFz2wHchLIDJT7pr81o zjZF87+f+qL33+nM8eDRzTzre6RQ7pmP2OYDAluQ= Date: Tue, 24 Jan 2023 13:11:22 -0800 From: Andrew Morton To: Andrey Konovalov Cc: andrey.konovalov@linux.dev, Marco Elver , Alexander Potapenko , Dmitry Vyukov , Andrey Ryabinin , kasan-dev@googlegroups.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrey Konovalov , Peter Collingbourne Subject: Re: [PATCH mm] kasan: reset page tags properly with sampling Message-Id: <20230124131122.fdbf6ae3069e6b0d05d14361@linux-foundation.org> In-Reply-To: References: <24ea20c1b19c2b4b56cf9f5b354915f8dbccfc77.1674592496.git.andreyknvl@google.com> <20230124124504.2b21f0fde58af208a4f4e290@linux-foundation.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: ADEB7100002 X-Rspam-User: X-Stat-Signature: mo8t9q9xdnxg4jt7oy45n7pbywjqzont X-HE-Tag: 1674594686-824769 X-HE-Meta: U2FsdGVkX19KAT5C+zmnS/+kCz1vR0+VglBuxoQ6JyompfCbJDdqGoCwpAhHqB9SOiI6LKBwi+4IF33rr5/3ikaq/9iRzFpw47/VNXaH+F5/VQqU1oMkPo4iL7uOtuVJVB/u9eaAiVH8uW/nWGhyF8qY2qSaF/qISinhVwLZwwdgX5MW+yDLGqVd+x/nEL5XWiw+UUeOwW5aBNEt6GOUIWDJQImBEPTch47CbdUXajAOPeCyMsDMIKTrXAJKNpQt4mLb8Ug/oWKLcq/DIZrfrVQ/QJWmIErNH2TNrBWd7YUy2fz+BzcJ0uKdqvXqmFHsJGaeyBYEvS0qKWn9+wwhG/34bbvJlZnTflPtbeG4Apt9QCXjZk1O7aLxxDo3f3Zt+ygcCBxMy1TMzQUMxkcV0cX70PZ40fdG3UHG2+Evlu7Tr2n3/uS5HTOo3+Kj3HdwAMFEdTZlg+1c7CbSKSiwCzhOYj5oKi0yVifVy0TPgXsorZ7Khaqf6+XgE5F6cRMiXaJKc0o+tDjl3p315HA+z94zSNhlr8arCVJUtAoQMxsdo85kh7shSEsiRb1KM1r8ZYTSASuPXIQUvuT9MGVz+jeS42hgDUJDKvJGQ/T7ZJi73MoVtiXpyVfVsWCmVgjqLtHBbXn2lPVZRrxgmI0XpfiH8LED53++at6T/ffxZCD/I6VCPRdk58V4BYoLQ0IkqY8TAGiqVpWlFnPxt8gBNZiGsCzjQh62HEBGqj6EkhBGTCjBUEOt5ovDmhbSGugXgJKEW95JcOulm9LFDjzsMs6m06U7JJuEwPhwZ9ygMbKcE12SEhSBxDN2iQirb1uXr3UBpHENnXtPFzNs55PtPLs1+LRDXkRRPorxHCjX90FQ7+psgr0iSu7FNXxcoKhXnz2u8DGPl4kl3AWMCQmFc4bTOn5rLUeByoGR0qPhSRuIlfihwdyqUnX5h7gth5Vv/bx/EySWD500oPEtk1M qDBOY1du 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 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: On Tue, 24 Jan 2023 21:46:51 +0100 Andrey Konovalov wrote: > On Tue, Jan 24, 2023 at 9:45 PM Andrew Morton wrote: > > > > On Tue, 24 Jan 2023 21:35:26 +0100 andrey.konovalov@linux.dev wrote: > > > > > The implementation of page_alloc poisoning sampling assumed that > > > tag_clear_highpage resets page tags for __GFP_ZEROTAGS allocations. > > > However, this is no longer the case since commit 70c248aca9e7 > > > ("mm: kasan: Skip unpoisoning of user pages"). > > > > > > This leads to kernel crashes when MTE-enabled userspace mappings are > > > used with Hardware Tag-Based KASAN enabled. > > > > > > Reset page tags for __GFP_ZEROTAGS allocations in post_alloc_hook(). > > > > > > Also clarify and fix related comments. > > > > I assume this is a fix against 44383cef54c0 ("kasan: allow sampling > > page_alloc allocations for HW_TAGS") which is presently in mm-stable, > > yes? > > Correct. I assumed I shouldn't include a Fixes tag, as the patch is > not in the mainline. I think it's best to add the Fixes: if it's known. If the patch was in mm-unstable then I'd just fold the fix into the base patch, but a Fixes: is still helpful because it tells people (especially me) which patch needs the fix. If the patch is in mm-stable then the SHA is stable and the Fixes: is desirable for people who are backporting the base patch into earlier kernels - hopefully when doing this they know to search the tree for other patches which fix the patch which they are backporting.