CVE-2026-68428: KVM: x86/mmu: Fix use-after-free on vendor module reload

CVE-2026-68428: KVM: x86/mmu: Fix use-after-free on vendor module reload

[Greg Kroah-Hartman]

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

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

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

KVM: x86/mmu: Fix use-after-free on vendor module reload

mmu_destroy_caches() destroys pte_list_desc_cache and
mmu_page_header_cache, but leaves both pointers unchanged.  The pointers
live in kvm.ko, and therefore survive when a vendor module is unloaded
while kvm.ko remains loaded.

If creation of pte_list_desc_cache fails during a subsequent vendor
module load, its assignment sets pte_list_desc_cache to NULL and the
error path calls mmu_destroy_caches().  mmu_page_header_cache still
points to the cache destroyed during the preceding vendor module
unload.  Passing that stale pointer to kmem_cache_destroy() causes a
slab use-after-free.

Reproduce the issue on a v7.1.3 kernel with CONFIG_KASAN=y,
CONFIG_KASAN_GENERIC=y, CONFIG_KVM=m, and CONFIG_KVM_INTEL=m.  A
one-shot test hook forces pte_list_desc_cache to NULL on the second
invocation of kvm_mmu_vendor_module_init():

  1. Load kvm.ko and kvm-intel.ko, creating both caches.
  2. Unload only kvm_intel, leaving kvm.ko loaded.
  3. Reload kvm_intel and force initialization through the -ENOMEM path.

KASAN reports:

  BUG: KASAN: slab-use-after-free in
  kvm_mmu_vendor_module_init+0x5b/0x170 [kvm]
  ...
  kmem_cache_destroy+0x21/0x1d0
  kvm_mmu_vendor_module_init+0x5b/0x170 [kvm]
  ...
  Allocated by task 16817:
  __kmem_cache_create_args+0x12c/0x3b0
  __kmem_cache_create.constprop.0+0xb6/0xf0 [kvm]
  kvm_mmu_vendor_module_init+0x13b/0x170 [kvm]
  ...
  Freed by task 16820:
  kmem_cache_destroy+0x117/0x1d0
  kvm_mmu_vendor_module_exit+0x21/0x30 [kvm]

Clear both pointers immediately after destroying their caches so that
the stored state reflects the caches' lifetime and repeated cleanup is
safe.

With the fix applied, the same injected vendor module reload fails with
-ENOMEM as expected and produces no KASAN report.

The Linux kernel CVE team has assigned CVE-2026-68428 to this issue.


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

	Issue introduced in 2.6.25 with commit cb498ea2ce1d3f3c0bc0a2522241dca10263e437 and fixed in 6.6.148 with commit 6f4be73880302d5642c83a0813fdfe1f5fd4b6e3
	Issue introduced in 2.6.25 with commit cb498ea2ce1d3f3c0bc0a2522241dca10263e437 and fixed in 6.12.101 with commit 32b9f89ed9e6d7a45075d64089c254a7f6e13695
	Issue introduced in 2.6.25 with commit cb498ea2ce1d3f3c0bc0a2522241dca10263e437 and fixed in 6.18.42 with commit ec9daa8fd1b6f45545c9839dca55bd867fad9e13
	Issue introduced in 2.6.25 with commit cb498ea2ce1d3f3c0bc0a2522241dca10263e437 and fixed in 7.1.6 with commit 43cfb20d62ffe49626d62beecfc32eb6f262191c
	Issue introduced in 2.6.25 with commit cb498ea2ce1d3f3c0bc0a2522241dca10263e437 and fixed in 7.2-rc5 with commit 52f2f7c30126037975389aa04d24c506a5177c35

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-2026-68428
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/x86/kvm/mmu/mmu.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/6f4be73880302d5642c83a0813fdfe1f5fd4b6e3
	https://git.kernel.org/stable/c/32b9f89ed9e6d7a45075d64089c254a7f6e13695
	https://git.kernel.org/stable/c/ec9daa8fd1b6f45545c9839dca55bd867fad9e13
	https://git.kernel.org/stable/c/43cfb20d62ffe49626d62beecfc32eb6f262191c
	https://git.kernel.org/stable/c/52f2f7c30126037975389aa04d24c506a5177c35