CVE-2026-93218: mm/huge_memory: skip device-private PMDs in madvise_free_huge_pmd

CVE-2026-93218: mm/huge_memory: skip device-private PMDs in madvise_free_huge_pmd

[Greg Kroah-Hartman]

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

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

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

mm/huge_memory: skip device-private PMDs in madvise_free_huge_pmd

madvise_free_pte_range() checks pmd_trans_huge(*pmd) unlocked, then
madvise_free_huge_pmd() takes pmd_trans_huge_lock().  pmd_is_huge()
returns true for a device-private PMD, so orig_pmd can be device-private
and enter the !pmd_present() branch.

Skip device-private PMDs in that non-present branch and continue to out
before calling pmd_folio().  Downgrade the check to VM_WARN_ON_ONCE() so
an unexpected PMD softleaf logs a warning rather than panicking.  Drop the
thp_migration_supported() guard: it expands to
IS_ENABLED(CONFIG_ARCH_SUPPORTS_PMD_SOFTLEAF), and both
pmd_is_migration_entry() and pmd_is_device_private_entry() already return
false when that config is not selected, so the guard suppresses only the
case where the warning would already be silent.

Potential trigger: an HMM-based GPU driver races with madvise(MADV_FREE):
migrate_vma_pages() flips the PMD to a device-private entry between the
caller's pmd_trans_huge() check and the callee's pmd_trans_huge_lock().

The Linux kernel CVE team has assigned CVE-2026-93218 to this issue.


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

	Issue introduced in 6.19 with commit 368076f52ebeecd33e10a9f80905d7508b6b6149 and fixed in 7.2.4 with commit 5e3026bf736498115884d6c7bd0308ba29e0474c
	Issue introduced in 6.19 with commit 368076f52ebeecd33e10a9f80905d7508b6b6149 and fixed in 7.3-rc1 with commit ce579dcf730ce5ed8043a5eeea18a3e6706a97e5

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-2026-93218
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/5e3026bf736498115884d6c7bd0308ba29e0474c
	https://git.kernel.org/stable/c/ce579dcf730ce5ed8043a5eeea18a3e6706a97e5