CVE-2026-64130: mm/page_alloc: fix initialization of tags of the huge zero folio with init_on_free

From: Greg Kroah-Hartman <[email protected]>

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

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

mm/page_alloc: fix initialization of tags of the huge zero folio with init_on_free

__GFP_ZEROTAGS semantics are currently a bit weird, but effectively this
flag is only ever set alongside __GFP_ZERO and __GFP_SKIP_KASAN.

If we run with init_on_free, we will zero out pages during
__free_pages_prepare(), to skip zeroing on the allocation path.

However, when allocating with __GFP_ZEROTAG set, post_alloc_hook() will
consequently not only skip clearing page content, but also skip clearing
tag memory.

Not clearing tags through __GFP_ZEROTAGS is irrelevant for most pages that
will get mapped to user space through set_pte_at() later: set_pte_at() and
friends will detect that the tags have not been initialized yet
(PG_mte_tagged not set), and initialize them.

However, for the huge zero folio, which will be mapped through a PMD
marked as special, this initialization will not be performed, ending up
exposing whatever tags were still set for the pages.

The docs (Documentation/arch/arm64/memory-tagging-extension.rst) state
that allocation tags are set to 0 when a page is first mapped to user
space.  That no longer holds with the huge zero folio when init_on_free is
enabled.

Fix it by decoupling __GFP_ZEROTAGS from __GFP_ZERO, passing to
tag_clear_highpages() whether we want to also clear page content.

Invert the meaning of the tag_clear_highpages() return value to have
clearer semantics.

Reproduced with the huge zero folio by modifying the check_buffer_fill
arm64/mte selftest to use a 2 MiB area, after making sure that pages have
a non-0 tag set when freeing (note that, during boot, we will not actually
initialize tags, but only set KASAN_TAG_KERNEL in the page flags).

	$ ./check_buffer_fill
	1..20
	...
	not ok 17 Check initial tags with private mapping, sync error mode and mmap memory
	not ok 18 Check initial tags with private mapping, sync error mode and mmap/mprotect memory
	...

This code needs more cleanups; we'll tackle that next, like
decoupling __GFP_ZEROTAGS from __GFP_SKIP_KASAN.

[[email protected]: s/__GPF_ZERO/__GFP_ZERO/, per David]

The Linux kernel CVE team has assigned CVE-2026-64130 to this issue.


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

	Issue introduced in 6.18 with commit adfb6609c6809e107ded9a1cd46f519c882e64ea and fixed in 6.18.34 with commit 738d18f1da3513d17b6f7bf30146cc4ac2480ffd
	Issue introduced in 6.18 with commit adfb6609c6809e107ded9a1cd46f519c882e64ea and fixed in 7.0.11 with commit 2f2aec5120b93a8f8b52dc50cdc60dbb8aec72f6
	Issue introduced in 6.18 with commit adfb6609c6809e107ded9a1cd46f519c882e64ea and fixed in 7.1 with commit 6a288a4ddb4a994490505ab5f41c445f8e6b6467

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-2026-64130
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:
	arch/arm64/include/asm/page.h
	arch/arm64/mm/fault.c
	include/linux/gfp_types.h
	include/linux/highmem.h
	mm/page_alloc.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/738d18f1da3513d17b6f7bf30146cc4ac2480ffd
	https://git.kernel.org/stable/c/2f2aec5120b93a8f8b52dc50cdc60dbb8aec72f6
	https://git.kernel.org/stable/c/6a288a4ddb4a994490505ab5f41c445f8e6b6467