CVE-2023-53208
Unknown Unknown - Not Provided
BaseFortify

Publication date: 2025-09-15

Last updated on: 2025-12-04

Assigner: kernel.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.
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Meta Information
Published
2025-09-15
Last Modified
2025-12-04
Generated
2026-05-07
AI Q&A
2025-09-15
EPSS Evaluated
2026-05-05
NVD
CVE-2023-53208
Affected Vendors & Products
Showing 2 associated CPEs
Vendor Product Version / Range
linux linux_kernel From 5.16 (inc) to 6.1.54 (exc)
linux linux_kernel From 6.2 (inc) to 6.5.4 (exc)
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-NVD-CWE-noinfo
Attack-Flow Graph
AI Powered Q&A
Can you explain this vulnerability to me?

This vulnerability involves the Linux kernel's KVM (Kernel-based Virtual Machine) nested virtualization feature for AMD processors. Specifically, it concerns how the Time Stamp Counter (TSC) multiplier for the first-level guest (L1) is loaded during nested VM exits. The issue arises because the kernel incorrectly assumes that TSC scaling is exposed to L1, but userspace can trigger warnings by manipulating model-specific registers (MSRs) and guest CPUID features. This can lead to repeated warnings and subtle behavior in KVM's handling of TSC multipliers during nested virtualization.


How can this vulnerability impact me? :

The vulnerability can cause repeated warnings and potentially unstable or unexpected behavior in nested virtualization environments using KVM on AMD processors. This may affect the reliability and performance of virtual machines running nested guests, but there is no indication of direct security compromise such as privilege escalation or data leakage.


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