linux-cve-announce - CVE-2022-49101: xen: delay xen_hvm_init_time

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Message-ID: <2025022600-CVE-2022-49101-e5e3@gregkh>
Date: Wed, 26 Feb 2025 02:55:06 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2022-49101: xen: delay xen_hvm_init_time_ops() if kdump is boot on vcpu>=32

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

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

xen: delay xen_hvm_init_time_ops() if kdump is boot on vcpu>=32

The sched_clock() can be used very early since commit 857baa87b642
("sched/clock: Enable sched clock early"). In addition, with commit
38669ba205d1 ("x86/xen/time: Output xen sched_clock time from 0"), kdump
kernel in Xen HVM guest may panic at very early stage when accessing
&__this_cpu_read(xen_vcpu)->time as in below:

setup_arch()
 -> init_hypervisor_platform()
     -> x86_init.hyper.init_platform = xen_hvm_guest_init()
         -> xen_hvm_init_time_ops()
             -> xen_clocksource_read()
                 -> src = &__this_cpu_read(xen_vcpu)->time;

This is because Xen HVM supports at most MAX_VIRT_CPUS=32 'vcpu_info'
embedded inside 'shared_info' during early stage until xen_vcpu_setup() is
used to allocate/relocate 'vcpu_info' for boot cpu at arbitrary address.

However, when Xen HVM guest panic on vcpu >= 32, since
xen_vcpu_info_reset(0) would set per_cpu(xen_vcpu, cpu) = NULL when
vcpu >= 32, xen_clocksource_read() on vcpu >= 32 would panic.

This patch calls xen_hvm_init_time_ops() again later in
xen_hvm_smp_prepare_boot_cpu() after the 'vcpu_info' for boot vcpu is
registered when the boot vcpu is >= 32.

This issue can be reproduced on purpose via below command at the guest
side when kdump/kexec is enabled:

"taskset -c 33 echo c > /proc/sysrq-trigger"

The bugfix for PVM is not implemented due to the lack of testing
environment.

[boris: xen_hvm_init_time_ops() returns on errors instead of jumping to end]

The Linux kernel CVE team has assigned CVE-2022-49101 to this issue.

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

	Fixed in 4.19.238 with commit 0848767dee78c00c5646eef9b3201ee14ce68563
	Fixed in 5.4.189 with commit 8a7462b5211cd5b74b8815034d038e28cbd96d52
	Fixed in 5.10.111 with commit a2a0e04f6478e8c1038db64717f3fafd55de1420
	Fixed in 5.15.34 with commit 5c0750cad73350e1c504eb91a94093a79f6f6296
	Fixed in 5.16.20 with commit be63f365f454e39d09c41bbd21ea72b5244160b5
	Fixed in 5.17.3 with commit b6f6b353d6c765b83c9e5e518a44ca1ae40fe227
	Fixed in 5.18 with commit eed05744322da07dd7e419432dcedf3c2e017179

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-2022-49101
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/xen/smp_hvm.c
	arch/x86/xen/time.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/0848767dee78c00c5646eef9b3201ee14ce68563
	https://git.kernel.org/stable/c/8a7462b5211cd5b74b8815034d038e28cbd96d52
	https://git.kernel.org/stable/c/a2a0e04f6478e8c1038db64717f3fafd55de1420
	https://git.kernel.org/stable/c/5c0750cad73350e1c504eb91a94093a79f6f6296
	https://git.kernel.org/stable/c/be63f365f454e39d09c41bbd21ea72b5244160b5
	https://git.kernel.org/stable/c/b6f6b353d6c765b83c9e5e518a44ca1ae40fe227
	https://git.kernel.org/stable/c/eed05744322da07dd7e419432dcedf3c2e017179