CVE-2026-46317: KVM: arm64: Reassign nested_mmus array behind mmu_lock

CVE-2026-46317: KVM: arm64: Reassign nested_mmus array behind mmu_lock

[Greg Kroah-Hartman]

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

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

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

KVM: arm64: Reassign nested_mmus array behind mmu_lock

kvm->arch.nested_mmus[] is walked under kvm->mmu_lock, including from the
MMU notifier path (kvm_unmap_gfn_range() -> kvm_nested_s2_unmap()), which
can run at any time. kvm_vcpu_init_nested() reallocates the array and frees
the old buffer while holding only kvm->arch.config_lock, so such a walker
can reference the freed array.

Allocate the new array outside of mmu_lock, as the allocation can sleep.
Under the lock, copy the existing entries, fix up the back pointers and
reassign the array. Free the old buffer after dropping the lock, as
kvfree() can sleep as well.

The Linux kernel CVE team has assigned CVE-2026-46317 to this issue.


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

	Issue introduced in 6.11 with commit 4f128f8e1aaac189f83d0f828bcdb2986d8d2e51 and fixed in 6.18.35 with commit 918450ad6010df6ecd2efde12a1409e011da22d6
	Issue introduced in 6.11 with commit 4f128f8e1aaac189f83d0f828bcdb2986d8d2e51 and fixed in 7.0.12 with commit 4424dbcb06d68e34e51c019a5781a7dc00731971
	Issue introduced in 6.11 with commit 4f128f8e1aaac189f83d0f828bcdb2986d8d2e51 and fixed in 7.1-rc7 with commit 70543358fa08e0f7cebc3447c3b70fe97ad7aaa8

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-2026-46317
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/kvm/nested.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/918450ad6010df6ecd2efde12a1409e011da22d6
	https://git.kernel.org/stable/c/4424dbcb06d68e34e51c019a5781a7dc00731971
	https://git.kernel.org/stable/c/70543358fa08e0f7cebc3447c3b70fe97ad7aaa8