linux-cve-announce - CVE-2025-38447: mm/rmap: fix potential out-of-bounds page table access during batched unmap

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Message-ID: <2025072503-CVE-2025-38447-5233@gregkh>
Date: Fri, 25 Jul 2025 17:28:09 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-38447: mm/rmap: fix potential out-of-bounds page table access during batched unmap

From: Greg Kroah-Hartman <gregkh@...nel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

mm/rmap: fix potential out-of-bounds page table access during batched unmap

As pointed out by David[1], the batched unmap logic in
try_to_unmap_one() may read past the end of a PTE table when a large
folio's PTE mappings are not fully contained within a single page
table.

While this scenario might be rare, an issue triggerable from userspace
must be fixed regardless of its likelihood.  This patch fixes the
out-of-bounds access by refactoring the logic into a new helper,
folio_unmap_pte_batch().

The new helper correctly calculates the safe batch size by capping the
scan at both the VMA and PMD boundaries.  To simplify the code, it also
supports partial batching (i.e., any number of pages from 1 up to the
calculated safe maximum), as there is no strong reason to special-case
for fully mapped folios.

The Linux kernel CVE team has assigned CVE-2025-38447 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 6.15 with commit 354dffd29575cdf13154e8fb787322354aa9efc4 and fixed in 6.15.7 with commit 510fe9c15d07e765d96be9a9dc37e5057c6c09f4
	Issue introduced in 6.15 with commit 354dffd29575cdf13154e8fb787322354aa9efc4 and fixed in 6.16-rc6 with commit ddd05742b45b083975a0855ef6ebbf88cf1f532a

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2025-38447
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	mm/rmap.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/510fe9c15d07e765d96be9a9dc37e5057c6c09f4
	https://git.kernel.org/stable/c/ddd05742b45b083975a0855ef6ebbf88cf1f532a