CVE-2026-46014

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]