linux-cve-announce - CVE-2025-37958: mm/huge_memory: fix dereferencing invalid pmd migration entry

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Message-ID: <2025052003-CVE-2025-37958-02de@gregkh>
Date: Tue, 20 May 2025 18:02:12 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-37958: mm/huge_memory: fix dereferencing invalid pmd migration entry

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

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

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

mm/huge_memory: fix dereferencing invalid pmd migration entry

When migrating a THP, concurrent access to the PMD migration entry during
a deferred split scan can lead to an invalid address access, as
illustrated below.  To prevent this invalid access, it is necessary to
check the PMD migration entry and return early.  In this context, there is
no need to use pmd_to_swp_entry and pfn_swap_entry_to_page to verify the
equality of the target folio.  Since the PMD migration entry is locked, it
cannot be served as the target.

Mailing list discussion and explanation from Hugh Dickins: "An anon_vma
lookup points to a location which may contain the folio of interest, but
might instead contain another folio: and weeding out those other folios is
precisely what the "folio != pmd_folio((*pmd)" check (and the "risk of
replacing the wrong folio" comment a few lines above it) is for."

BUG: unable to handle page fault for address: ffffea60001db008
CPU: 0 UID: 0 PID: 2199114 Comm: tee Not tainted 6.14.0+ #4 NONE
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:split_huge_pmd_locked+0x3b5/0x2b60
Call Trace:
<TASK>
try_to_migrate_one+0x28c/0x3730
rmap_walk_anon+0x4f6/0x770
unmap_folio+0x196/0x1f0
split_huge_page_to_list_to_order+0x9f6/0x1560
deferred_split_scan+0xac5/0x12a0
shrinker_debugfs_scan_write+0x376/0x470
full_proxy_write+0x15c/0x220
vfs_write+0x2fc/0xcb0
ksys_write+0x146/0x250
do_syscall_64+0x6a/0x120
entry_SYSCALL_64_after_hwframe+0x76/0x7e

The bug is found by syzkaller on an internal kernel, then confirmed on
upstream.

The Linux kernel CVE team has assigned CVE-2025-37958 to this issue.


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

	Issue introduced in 4.14 with commit 84c3fc4e9c563d8fb91cfdf5948da48fe1af34d3 and fixed in 6.12.29 with commit 6166c3cf405441f7147b322980144feb3cefc617
	Issue introduced in 4.14 with commit 84c3fc4e9c563d8fb91cfdf5948da48fe1af34d3 and fixed in 6.14.7 with commit fbab262b0c8226c697af1851a424896ed47dedcc
	Issue introduced in 4.14 with commit 84c3fc4e9c563d8fb91cfdf5948da48fe1af34d3 and fixed in 6.15-rc6 with commit be6e843fc51a584672dfd9c4a6a24c8cb81d5fb7

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-2025-37958
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/huge_memory.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/6166c3cf405441f7147b322980144feb3cefc617
	https://git.kernel.org/stable/c/fbab262b0c8226c697af1851a424896ed47dedcc
	https://git.kernel.org/stable/c/be6e843fc51a584672dfd9c4a6a24c8cb81d5fb7