PT-2026-43881 · Linux · Linux
Published
2026-05-27
·
Updated
2026-05-27
·
CVE-2026-46014
None
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In the Linux kernel, the following vulnerability has been resolved:
KVM: SVM: Add missing save/restore handling of LBR MSRs
MSR IA32 DEBUGCTLMSR and LBR MSRs are currently not enumerated by
KVM GET MSR INDEX LIST, and LBR MSRs cannot be set with KVM SET MSRS. So
save/restore is completely broken.
Fix it by adding the MSRs to msrs to save base, and allowing writes to
LBR MSRs from userspace only (as they are read-only MSRs) if LBR
virtualization is enabled. Additionally, to correctly restore L1's LBRs
while L2 is running, make sure the LBRs are copied from the captured
VMCB01 save area in svm copy vmrun state().
Note, for VMX, this also fixes a flaw where MSR IA32 DEBUGCTLMSR isn't
reported as an MSR to save/restore.
Note #2, over-reporting MSR IA32 LASTxxx on Intel is ok, as KVM already
handles unsupported reads and writes thanks to commit b5e2fec0ebc3 ("KVM:
Ignore DEBUGCTL MSRs with no effect") (kvm do msr access() will morph the
unsupported userspace write into a nop).
[sean: guard with lbrv checks, massage changelog]
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Related Identifiers
Affected Products
Linux