Subject: CVE-2024-35791: KVM: SVM: Flush pages under kvm->lock to fix UAF in svm_register_enc_region()

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

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

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

KVM: SVM: Flush pages under kvm->lock to fix UAF in svm_register_enc_region()

Do the cache flush of converted pages in svm_register_enc_region() before
dropping kvm->lock to fix use-after-free issues where region and/or its
array of pages could be freed by a different task, e.g. if userspace has
__unregister_enc_region_locked() already queued up for the region.

Note, the "obvious" alternative of using local variables doesn't fully
resolve the bug, as region->pages is also dynamically allocated.  I.e. the
region structure itself would be fine, but region->pages could be freed.

Flushing multiple pages under kvm->lock is unfortunate, but the entire
flow is a rare slow path, and the manual flush is only needed on CPUs that
lack coherency for encrypted memory.

The Linux kernel CVE team has assigned CVE-2024-35791 to this issue.

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

	Issue introduced in 5.10.15 with commit 4f627ecde732 and fixed in 5.10.215 with commit 2d13b79640b1
	Issue introduced in 5.11 with commit 19a23da53932 and fixed in 5.15.154 with commit e126b508ed2e
	Issue introduced in 5.11 with commit 19a23da53932 and fixed in 6.1.84 with commit 4868c0ecdb6c
	Issue introduced in 5.11 with commit 19a23da53932 and fixed in 6.6.24 with commit 12f8e32a5a38
	Issue introduced in 5.11 with commit 19a23da53932 and fixed in 6.7.12 with commit f6d53d8a2617
	Issue introduced in 5.11 with commit 19a23da53932 and fixed in 6.8 with commit 5ef1d8c1ddbf
	Issue introduced in 4.19.176 with commit f1ecde00ce16
	Issue introduced in 5.4.98 with commit 848bcb0a1d96

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-2024-35791
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

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/2d13b79640b147bd77c34a5998533b2021a4122d
	https://git.kernel.org/stable/c/e126b508ed2e616d679d85fca2fbe77bb48bbdd7
	https://git.kernel.org/stable/c/4868c0ecdb6cfde7c70cf478c46e06bb9c7e5865
	https://git.kernel.org/stable/c/12f8e32a5a389a5d58afc67728c76e61beee1ad4
	https://git.kernel.org/stable/c/f6d53d8a2617dd58c89171a6b9610c470ebda38a
	https://git.kernel.org/stable/c/5ef1d8c1ddbf696e47b226e11888eaf8d9e8e807