linux-cve-announce - CVE-2024-58083: KVM: Explicitly verify target vCPU is online in kvm_get

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Message-ID: <2025030610-CVE-2024-58083-62b7@gregkh>
Date: Thu,  6 Mar 2025 17:14:16 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2024-58083: KVM: Explicitly verify target vCPU is online in kvm_get_vcpu()

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

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

KVM: Explicitly verify target vCPU is online in kvm_get_vcpu()

Explicitly verify the target vCPU is fully online _prior_ to clamping the
index in kvm_get_vcpu().  If the index is "bad", the nospec clamping will
generate '0', i.e. KVM will return vCPU0 instead of NULL.

In practice, the bug is unlikely to cause problems, as it will only come
into play if userspace or the guest is buggy or misbehaving, e.g. KVM may
send interrupts to vCPU0 instead of dropping them on the floor.

However, returning vCPU0 when it shouldn't exist per online_vcpus is
problematic now that KVM uses an xarray for the vCPUs array, as KVM needs
to insert into the xarray before publishing the vCPU to userspace (see
commit c5b077549136 ("KVM: Convert the kvm->vcpus array to a xarray")),
i.e. before vCPU creation is guaranteed to succeed.

As a result, incorrectly providing access to vCPU0 will trigger a
use-after-free if vCPU0 is dereferenced and kvm_vm_ioctl_create_vcpu()
bails out of vCPU creation due to an error and frees vCPU0.  Commit
afb2acb2e3a3 ("KVM: Fix vcpu_array[0] races") papered over that issue, but
in doing so introduced an unsolvable teardown conundrum.  Preventing
accesses to vCPU0 before it's fully online will allow reverting commit
afb2acb2e3a3, without re-introducing the vcpu_array[0] UAF race.

The Linux kernel CVE team has assigned CVE-2024-58083 to this issue.

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

	Issue introduced in 5.1 with commit 1d487e9bf8ba66a7174c56a0029c54b1eca8f99c and fixed in 6.1.129 with commit d817e510662fd1c9797952408d94806f97a5fffd
	Issue introduced in 5.1 with commit 1d487e9bf8ba66a7174c56a0029c54b1eca8f99c and fixed in 6.6.78 with commit 125da53b3c0c9d7f58353aea0076e9efd6498ba7
	Issue introduced in 5.1 with commit 1d487e9bf8ba66a7174c56a0029c54b1eca8f99c and fixed in 6.12.14 with commit f2f805ada63b536bc192458a7098388286568ad4
	Issue introduced in 5.1 with commit 1d487e9bf8ba66a7174c56a0029c54b1eca8f99c and fixed in 6.13.3 with commit ca8da90ed1432ff3d000de4f1e2275d4e7d21b96
	Issue introduced in 5.1 with commit 1d487e9bf8ba66a7174c56a0029c54b1eca8f99c and fixed in 6.14-rc1 with commit 1e7381f3617d14b3c11da80ff5f8a93ab14cfc46
	Issue introduced in 4.14.120 with commit 559e2696d2f47a3575e9550f101a7e59e30b1b38
	Issue introduced in 4.19.44 with commit d39f3cc71382165bb7efb8e06a2bd32f847de4ae
	Issue introduced in 5.0.17 with commit 7cee966029037a183d98cb88251ceb92a233fe63

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-2024-58083
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:
	include/linux/kvm_host.h

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/d817e510662fd1c9797952408d94806f97a5fffd
	https://git.kernel.org/stable/c/125da53b3c0c9d7f58353aea0076e9efd6498ba7
	https://git.kernel.org/stable/c/f2f805ada63b536bc192458a7098388286568ad4
	https://git.kernel.org/stable/c/ca8da90ed1432ff3d000de4f1e2275d4e7d21b96
	https://git.kernel.org/stable/c/1e7381f3617d14b3c11da80ff5f8a93ab14cfc46