linux-cve-announce - CVE-2023-53208: KVM: nSVM: Load L1's TSC multiplier based on L1 state, not L2 state

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Message-ID: <2025091510-CVE-2023-53208-b31d@gregkh>
Date: Mon, 15 Sep 2025 16:21:42 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2023-53208: KVM: nSVM: Load L1's TSC multiplier based on L1 state, not L2 state

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

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

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

KVM: nSVM: Load L1's TSC multiplier based on L1 state, not L2 state

When emulating nested VM-Exit, load L1's TSC multiplier if L1's desired
ratio doesn't match the current ratio, not if the ratio L1 is using for
L2 diverges from the default.  Functionally, the end result is the same
as KVM will run L2 with L1's multiplier if L2's multiplier is the default,
i.e. checking that L1's multiplier is loaded is equivalent to checking if
L2 has a non-default multiplier.

However, the assertion that TSC scaling is exposed to L1 is flawed, as
userspace can trigger the WARN at will by writing the MSR and then
updating guest CPUID to hide the feature (modifying guest CPUID is
allowed anytime before KVM_RUN).  E.g. hacking KVM's state_test
selftest to do

                vcpu_set_msr(vcpu, MSR_AMD64_TSC_RATIO, 0);
                vcpu_clear_cpuid_feature(vcpu, X86_FEATURE_TSCRATEMSR);

after restoring state in a new VM+vCPU yields an endless supply of:

  ------------[ cut here ]------------
  WARNING: CPU: 10 PID: 206939 at arch/x86/kvm/svm/nested.c:1105
           nested_svm_vmexit+0x6af/0x720 [kvm_amd]
  Call Trace:
   nested_svm_exit_handled+0x102/0x1f0 [kvm_amd]
   svm_handle_exit+0xb9/0x180 [kvm_amd]
   kvm_arch_vcpu_ioctl_run+0x1eab/0x2570 [kvm]
   kvm_vcpu_ioctl+0x4c9/0x5b0 [kvm]
   ? trace_hardirqs_off+0x4d/0xa0
   __se_sys_ioctl+0x7a/0xc0
   __x64_sys_ioctl+0x21/0x30
   do_syscall_64+0x41/0x90
   entry_SYSCALL_64_after_hwframe+0x63/0xcd

Unlike the nested VMRUN path, hoisting the svm->tsc_scaling_enabled check
into the if-statement is wrong as KVM needs to ensure L1's multiplier is
loaded in the above scenario.   Alternatively, the WARN_ON() could simply
be deleted, but that would make KVM's behavior even more subtle, e.g. it's
not immediately obvious why it's safe to write MSR_AMD64_TSC_RATIO when
checking only tsc_ratio_msr.

The Linux kernel CVE team has assigned CVE-2023-53208 to this issue.

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

	Issue introduced in 5.16 with commit 5228eb96a4875f8cf5d61d486e3795ac14df8904 and fixed in 6.1.54 with commit 5b2b0535fa7adee7e295fed0a3095082131a8d05
	Issue introduced in 5.16 with commit 5228eb96a4875f8cf5d61d486e3795ac14df8904 and fixed in 6.5.4 with commit e91c07f6cf7060d2acb3aeee31a6baebe3773d3f
	Issue introduced in 5.16 with commit 5228eb96a4875f8cf5d61d486e3795ac14df8904 and fixed in 6.6 with commit 0c94e2468491cbf0754f49a5136ab51294a96b69

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-2023-53208
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

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/5b2b0535fa7adee7e295fed0a3095082131a8d05
	https://git.kernel.org/stable/c/e91c07f6cf7060d2acb3aeee31a6baebe3773d3f
	https://git.kernel.org/stable/c/0c94e2468491cbf0754f49a5136ab51294a96b69