linux-kernel - Re: [PATCH v1] mm: kmsan: Fix poisoning of high-order non-compound pages

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Message-ID: <CAG_fn=XtONeeJzBFFyxqWa1=Zo8bCGcUPO11Kaa4093vJOPgrA@mail.gmail.com>
Date: Mon, 12 Jan 2026 15:38:09 +0100
From: Alexander Potapenko <glider@...gle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Ryan Roberts <ryan.roberts@....com>, Marco Elver <elver@...gle.com>, 
	Dmitry Vyukov <dvyukov@...gle.com>, kasan-dev@...glegroups.com, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v1] mm: kmsan: Fix poisoning of high-order non-compound pages

On Sun, Jan 4, 2026 at 7:02 PM Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> On Sun,  4 Jan 2026 13:43:47 +0000 Ryan Roberts <ryan.roberts@....com> 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@...r.kernel.org
> > Signed-off-by: Ryan Roberts <ryan.roberts@....com>
Reviewed-by: Alexander Potapenko <glider@...gle.com>
Tested-by: Alexander Potapenko <glider@...gle.com>

Thanks!
I'll send out a follow-up patch with a test for this behavior.