CVE-2026-98505: mm/damon/vaddr: avoid hw-driven pte updates during damon_hugetlb_mkold()

CVE-2026-98505: mm/damon/vaddr: avoid hw-driven pte updates during damon_hugetlb_mkold()

[Greg Kroah-Hartman]

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

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

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

mm/damon/vaddr: avoid hw-driven pte updates during damon_hugetlb_mkold()

damon_hugetlb_mkold() reads the page table entry into a local variable,
unsets the accessed bit in the variable, and updates the page table entry
with the updated variable value.  If hardware updates the same page table
entry in parallel, the hw updates could be lost.  For example,
hardware-updated dirty bits might be lost.

Avoid the parallel updates by clearing the page table entry when reading
it together, using huge_ptep_get_and_clear().  If a parallel write to the
memory is made after the clearing, the hw will see the page table entry is
cleared, trigger page fault and wait until it is handled.  The page fault
handling will wait for damon_hugetlb_mkold() due to the page table lock.

Because hugetlbfs is an in-memory file system and hugetlb pages cannot be
reclaimed, no critical issue is expected to my best knowledge.  But
definitely this is a nasty bug that should be fixed sooner rather than
later.

The issue was discovered [1] by Sashiko.

The Linux kernel CVE team has assigned CVE-2026-98505 to this issue.


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

	Issue introduced in 5.17 with commit 49f4203aae06ba9d67b500c90339b262b0a52637 and fixed in 6.12.112 with commit 00457981327c80bcc56e07d4714fe189337a19fa
	Issue introduced in 5.17 with commit 49f4203aae06ba9d67b500c90339b262b0a52637 and fixed in 6.18.55 with commit e59cb7eda7c06334a0faf5aa44adb6acf2a1287a
	Issue introduced in 5.17 with commit 49f4203aae06ba9d67b500c90339b262b0a52637 and fixed in 7.2.9 with commit 6e74ffc9ecf6ec24eee117150da78a1102be74c5
	Issue introduced in 5.17 with commit 49f4203aae06ba9d67b500c90339b262b0a52637 and fixed in 7.3-rc5 with commit 39c0ceedd54557bdc1542de08d22b2ed33e534e4

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-2026-98505
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/damon/vaddr.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/00457981327c80bcc56e07d4714fe189337a19fa
	https://git.kernel.org/stable/c/e59cb7eda7c06334a0faf5aa44adb6acf2a1287a
	https://git.kernel.org/stable/c/6e74ffc9ecf6ec24eee117150da78a1102be74c5
	https://git.kernel.org/stable/c/39c0ceedd54557bdc1542de08d22b2ed33e534e4