linux-kernel - Re: [PATCH 1/3] mm/pagemap: Fix ioctl(PAGEMAP

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Message-ID: <b930ef9c-8795-40f6-bcad-11d081f65e5e@redhat.com>
Date:   Fri, 17 Nov 2023 00:10:16 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Peter Xu <peterx@...hat.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Cc:     Muhammad Usama Anjum <usama.anjum@...labora.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrei Vagin <avagin@...il.com>,
        syzbot+e94c5aaf7890901ebf9b@...kaller.appspotmail.com
Subject: Re: [PATCH 1/3] mm/pagemap: Fix ioctl(PAGEMAP_SCAN) on vma check

On 16.11.23 21:15, Peter Xu wrote:
> The new ioctl(PAGEMAP_SCAN) relies on vma wr-protect capability provided by
> userfault, however in the vma test it didn't explicitly require the vma to
> have wr-protect function enabled, even if PM_SCAN_WP_MATCHING flag is set.
> 
> It means the pagemap code can now apply uffd-wp bit to a page in the vma
> even if not registered to userfaultfd at all.
> 
> Then in whatever way as long as the pte got written and page fault
> resolved, we'll apply the write bit even if uffd-wp bit is set.  We'll see
> a pte that has both UFFD_WP and WRITE bit set.  Anything later that looks
> up the pte for uffd-wp bit will trigger the warning:
> 
> WARNING: CPU: 1 PID: 5071 at arch/x86/include/asm/pgtable.h:403 pte_uffd_wp arch/x86/include/asm/pgtable.h:403 [inline]
> 
> Fix it by doing proper check over the vma attributes when
> PM_SCAN_WP_MATCHING is specified.
> 
> Fixes: 52526ca7fdb9 ("fs/proc/task_mmu: implement IOCTL to get and optionally clear info about PTEs")
> Reported-by: syzbot+e94c5aaf7890901ebf9b@...kaller.appspotmail.com
> Signed-off-by: Peter Xu <peterx@...hat.com>
> ---

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb