cve/published/2022/CVE-2022-49559.mbox

From bippy-5f407fcff5a0 Mon Sep 17 00:00:00 2001
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: <linux-cve-announce@vger.kernel.org>
Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org>
Subject: CVE-2022-49559: KVM: x86: Drop WARNs that assert a triple fault never "escapes" from L2

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

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

KVM: x86: Drop WARNs that assert a triple fault never "escapes" from L2

Remove WARNs that sanity check that KVM never lets a triple fault for L2
escape and incorrectly end up in L1.  In normal operation, the sanity
check is perfectly valid, but it incorrectly assumes that it's impossible
for userspace to induce KVM_REQ_TRIPLE_FAULT without bouncing through
KVM_RUN (which guarantees kvm_check_nested_state() will see and handle
the triple fault).

The WARN can currently be triggered if userspace injects a machine check
while L2 is active and CR4.MCE=0.  And a future fix to allow save/restore
of KVM_REQ_TRIPLE_FAULT, e.g. so that a synthesized triple fault isn't
lost on migration, will make it trivially easy for userspace to trigger
the WARN.

Clearing KVM_REQ_TRIPLE_FAULT when forcibly leaving guest mode is
tempting, but wrong, especially if/when the request is saved/restored,
e.g. if userspace restores events (including a triple fault) and then
restores nested state (which may forcibly leave guest mode).  Ignoring
the fact that KVM doesn't currently provide the necessary APIs, it's
userspace's responsibility to manage pending events during save/restore.

  ------------[ cut here ]------------
  WARNING: CPU: 7 PID: 1399 at arch/x86/kvm/vmx/nested.c:4522 nested_vmx_vmexit+0x7fe/0xd90 [kvm_intel]
  Modules linked in: kvm_intel kvm irqbypass
  CPU: 7 PID: 1399 Comm: state_test Not tainted 5.17.0-rc3+ #808
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
  RIP: 0010:nested_vmx_vmexit+0x7fe/0xd90 [kvm_intel]
  Call Trace:
   <TASK>
   vmx_leave_nested+0x30/0x40 [kvm_intel]
   vmx_set_nested_state+0xca/0x3e0 [kvm_intel]
   kvm_arch_vcpu_ioctl+0xf49/0x13e0 [kvm]
   kvm_vcpu_ioctl+0x4b9/0x660 [kvm]
   __x64_sys_ioctl+0x83/0xb0
   do_syscall_64+0x3b/0xc0
   entry_SYSCALL_64_after_hwframe+0x44/0xae
   </TASK>
  ---[ end trace 0000000000000000 ]---

The Linux kernel CVE team has assigned CVE-2022-49559 to this issue.


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

	Issue introduced in 5.13 with commit cb6a32c2b8777ad31a02e585584d869251a790e3 and fixed in 5.15.45 with commit 8d3a2aa0976f57320ba89baf9d57fb158dd0cd0d
	Issue introduced in 5.13 with commit cb6a32c2b8777ad31a02e585584d869251a790e3 and fixed in 5.17.13 with commit f476a59d5c86c02a79eef893c6da86735f2977ac
	Issue introduced in 5.13 with commit cb6a32c2b8777ad31a02e585584d869251a790e3 and fixed in 5.18.2 with commit 7de373c9b48229e428ecdb8fbde269c5a8617fd2
	Issue introduced in 5.13 with commit cb6a32c2b8777ad31a02e585584d869251a790e3 and fixed in 5.19 with commit 45846661d10422ce9e22da21f8277540b29eca22

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-2022-49559
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/nested.c
	arch/x86/kvm/vmx/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/8d3a2aa0976f57320ba89baf9d57fb158dd0cd0d
	https://git.kernel.org/stable/c/f476a59d5c86c02a79eef893c6da86735f2977ac
	https://git.kernel.org/stable/c/7de373c9b48229e428ecdb8fbde269c5a8617fd2
	https://git.kernel.org/stable/c/45846661d10422ce9e22da21f8277540b29eca22