From: David Hildenbrand <david@redhat.com>
To: Jann Horn <jannh@google.com>,
security@kernel.org, Andrew Morton <akpm@linux-foundation.org>
Cc: Yang Shi <shy828301@gmail.com>, Peter Xu <peterx@redhat.com>,
John Hubbard <jhubbard@nvidia.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v3 3/3] mm/khugepaged: Invoke MMU notifiers in shmem/file collapse paths
Date: Mon, 28 Nov 2022 18:37:47 +0100 [thread overview]
Message-ID: <66cfc9ba-868c-9620-fbfc-38931c76ff50@redhat.com> (raw)
In-Reply-To: <20221125213714.4115729-3-jannh@google.com>
On 25.11.22 22:37, Jann Horn wrote:
> Any codepath that zaps page table entries must invoke MMU notifiers to
> ensure that secondary MMUs (like KVM) don't keep accessing pages which
> aren't mapped anymore. Secondary MMUs don't hold their own references to
> pages that are mirrored over, so failing to notify them can lead to page
> use-after-free.
>
> I'm marking this as addressing an issue introduced in commit f3f0e1d2150b
> ("khugepaged: add support of collapse for tmpfs/shmem pages"), but most of
> the security impact of this only came in commit 27e1f8273113 ("khugepaged:
> enable collapse pmd for pte-mapped THP"), which actually omitted flushes
> for the removal of present PTEs, not just for the removal of empty page
> tables.
>
> Cc: stable@kernel.org
> Fixes: f3f0e1d2150b ("khugepaged: add support of collapse for tmpfs/shmem pages")
I'm curious, do you have a working reproducer for this?
Change looks sane on quick glimpse.
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2022-11-28 17:39 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-25 21:37 [PATCH v3 1/3] mm/khugepaged: Take the right locks for page table retraction Jann Horn
2022-11-25 21:37 ` [PATCH v3 2/3] mm/khugepaged: Fix GUP-fast interaction by sending IPI Jann Horn
2022-11-28 13:46 ` David Hildenbrand
2022-11-28 16:58 ` Jann Horn
2022-11-28 17:00 ` David Hildenbrand
2022-11-25 21:37 ` [PATCH v3 3/3] mm/khugepaged: Invoke MMU notifiers in shmem/file collapse paths Jann Horn
2022-11-28 17:37 ` David Hildenbrand [this message]
2022-11-28 17:57 ` Jann Horn
2022-11-28 18:06 ` David Hildenbrand
2022-11-28 13:52 ` [PATCH v3 1/3] mm/khugepaged: Take the right locks for page table retraction David Hildenbrand
2022-11-28 17:28 ` Jann Horn
2022-11-28 17:34 ` David Hildenbrand
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