CVE-2026-64285: KVM: SEV: Pin source page for write when adding CPUID data for SNP guest

CVE-2026-64285: KVM: SEV: Pin source page for write when adding CPUID data for SNP guest

[Greg Kroah-Hartman]

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

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

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

KVM: SEV: Pin source page for write when adding CPUID data for SNP guest

When populating a guest_memfd instance with the initial CPUID data for an
SNP guest, acquire a writable pin on the source page as KVM will write back
the "correct" CPUID information if the userspace provided data is rejected
by trusted firmware.  Because KVM writes to the source page using a kernel
mapping, pinning for read could result in KVM clobbering read-only memory.

Note, well-behaved VMMs are unlikely to be affected, as CPUID information
is almost always dynamically generated by userspace, i.e. it's unlikely for
the CPUID information to be backed by a read-only mapping.

[sean: rewrite shortlog and changelog, tag for stable@]

The Linux kernel CVE team has assigned CVE-2026-64285 to this issue.


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

	Issue introduced in 7.0 with commit 2a62345b30529e488beb6a1220577b3495933724 and fixed in 7.1.4 with commit dcdb476f5fc5701ec06c23efe3e3529f07ca391e
	Issue introduced in 7.0 with commit 2a62345b30529e488beb6a1220577b3495933724 and fixed in 7.2-rc1 with commit f13e900599089b10113ceb36013423f0837c6792

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-2026-64285
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/svm/sev.c
	arch/x86/kvm/vmx/tdx.c
	include/linux/kvm_host.h
	virt/kvm/guest_memfd.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/dcdb476f5fc5701ec06c23efe3e3529f07ca391e
	https://git.kernel.org/stable/c/f13e900599089b10113ceb36013423f0837c6792