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b=LpJQM6hoUi+Q1YVYh08n8HeejbFS9R3NXWrFc0lipnhub04SnG50puKjpQV51KYiR HAI2oInhTrkk62gEqsOEchHIehRWy+QiJ8nwL11yPm4BIU1RJf6Ypr/XNICDJsI5E2 +IuuUVccAB3441KNKabMLqFiklxzjd7b/v8xlCHk= Date: Sun, 4 Jan 2026 10:02:30 -0800 From: Andrew Morton To: Ryan Roberts Cc: Alexander Potapenko , Marco Elver , Dmitry Vyukov , kasan-dev@googlegroups.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v1] mm: kmsan: Fix poisoning of high-order non-compound pages Message-Id: <20260104100230.09abd1beaca2123d174022b2@linux-foundation.org> In-Reply-To: <20260104134348.3544298-1-ryan.roberts@arm.com> References: <20260104134348.3544298-1-ryan.roberts@arm.com> 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: rspam12 X-Rspamd-Queue-Id: F003320011 X-Stat-Signature: wkxtnmogta1e96tppbi5q53juxaquai7 X-Rspam-User: X-HE-Tag: 1767549752-104843 X-HE-Meta: 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 Zw3feKzP X+yiRfU9PkvxaDtNE3RvedBJ1NJyR8Kajiaf/ombbfjRfQ4ydeUgqt3iCLm3isD/8gYAS1arOYZCnBe47L14s59xA1XWm+LHqITuYlVZ2Er6nUI/hiyMpLWxH9xZRonJhQtjPpgWEWggEYXvky1B6YuHjvf1C3sbUUXJ9SwA5Ka6Urgo3tLH8IENqIhbTNS8etLRsLDXr1mwoN8gX6ymH+GQJkx29TbeqhCCx2RmYozC4UqkSz0XStb0mESVK52FrxX2vmJwKluFNVi/Vk8kRDZD1umnLsiU94A2QtmgkDIsomG55iVbSkB0fCiAwBjB+0laMgYs6hBqPc/g= 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 Sun, 4 Jan 2026 13:43:47 +0000 Ryan Roberts wrote: > kmsan_free_page() is called by the page allocator's free_pages_prepare() > during page freeing. It's job is to poison all the memory covered by the > page. It can be called with an order-0 page, a compound high-order page > or a non-compound high-order page. But page_size() only works for > order-0 and compound pages. For a non-compound high-order page it will > incorrectly return PAGE_SIZE. > > The implication is that the tail pages of a high-order non-compound page > do not get poisoned at free, so any invalid access while they are free > could go unnoticed. It looks like the pages will be poisoned again at > allocaiton time, so that would bookend the window. > > Fix this by using the order parameter to calculate the size. > > Fixes: b073d7f8aee4 ("mm: kmsan: maintain KMSAN metadata for page operations") > Cc: stable@vger.kernel.org > Signed-off-by: Ryan Roberts > --- > > Hi, > > I noticed this during code review, so perhaps I've just misunderstood the intent > of the code. > > I don't have the means to compile and run on x86 with KMSAN enabled though, so > punting this out hoping someone might be able to validate/test. I guess there is > a small chance this could lead to KMSAN finding some new issues? We'll see, I'll park this in mm-new to get it a little testing, see if anything is shaken out. If all looks good and if the KMSAN maintainers are OK with it I'll later move the patch into mm-hotfixes for more expedited upstreaming.