From: Yosry Ahmed <yosry@kernel.org> stable inclusion from stable-v6.18.27 commit 2b922a42b531a82d7881add14a7698dcdc5e1f0a category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/15261 CVE: CVE-2026-46014 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- commit 3700f0788da6acf73b2df56690f4b201aa4aefd2 upstream. 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). Fixes: 24e09cbf480a ("KVM: SVM: enable LBR virtualization") Cc: stable@vger.kernel.org Reported-by: Jim Mattson <jmattson@google.com> Signed-off-by: Yosry Ahmed <yosry@kernel.org> Link: https://patch.msgid.link/20260303003421.2185681-4-yosry@kernel.org [sean: guard with lbrv checks, massage changelog] Signed-off-by: Sean Christopherson <seanjc@google.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Conflicts: arch/x86/kvm/svm/nested.c arch/x86/kvm/svm/svm.c arch/x86/kvm/x86.c [context conflicts and a3f0981a5a0e ("KVM: nSVM: Avoid clearing VMCB_LBR in vmcb12") not merged, which delete the vmcb_mark_dirty from `svm_copy_lbrs`] Signed-off-by: Zhang Kunbo <zhangkunbo@huawei.com> --- arch/x86/kvm/svm/nested.c | 10 ++++++++++ arch/x86/kvm/svm/svm.c | 42 ++++++++++++++++++++++++++++++++++----- arch/x86/kvm/x86.c | 3 +++ 3 files changed, 50 insertions(+), 5 deletions(-) diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c index 2cd9299b250e..146ab1ea390e 100644 --- a/arch/x86/kvm/svm/nested.c +++ b/arch/x86/kvm/svm/nested.c @@ -969,6 +969,16 @@ void svm_copy_vmrun_state(struct vmcb_save_area *to_save, to_save->rsp = from_save->rsp; to_save->rip = from_save->rip; to_save->cpl = 0; + + if (kvm_cpu_cap_has(X86_FEATURE_LBRV)) { + to_save->dbgctl = from_save->dbgctl; + to_save->br_from = from_save->br_from; + to_save->br_to = from_save->br_to; + to_save->last_excp_from = from_save->last_excp_from; + to_save->last_excp_to = from_save->last_excp_to; + + to_save->dbgctl &= ~DEBUGCTL_RESERVED_BITS; + } } void svm_copy_vmloadsave_state(struct vmcb *to_vmcb, struct vmcb *from_vmcb) diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index 06d0d8706ba4..8a299fa2f47a 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -2941,19 +2941,19 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) msr_info->data = svm->tsc_aux; break; case MSR_IA32_DEBUGCTLMSR: - msr_info->data = svm_get_lbr_vmcb(svm)->save.dbgctl; + msr_info->data = lbrv ? svm_get_lbr_vmcb(svm)->save.dbgctl : 0; break; case MSR_IA32_LASTBRANCHFROMIP: - msr_info->data = svm_get_lbr_vmcb(svm)->save.br_from; + msr_info->data = lbrv ? svm_get_lbr_vmcb(svm)->save.br_from : 0; break; case MSR_IA32_LASTBRANCHTOIP: - msr_info->data = svm_get_lbr_vmcb(svm)->save.br_to; + msr_info->data = lbrv ? svm_get_lbr_vmcb(svm)->save.br_to : 0; break; case MSR_IA32_LASTINTFROMIP: - msr_info->data = svm_get_lbr_vmcb(svm)->save.last_excp_from; + msr_info->data = lbrv ? svm_get_lbr_vmcb(svm)->save.last_excp_from : 0; break; case MSR_IA32_LASTINTTOIP: - msr_info->data = svm_get_lbr_vmcb(svm)->save.last_excp_to; + msr_info->data = lbrv ? svm_get_lbr_vmcb(svm)->save.last_excp_to : 0; break; case MSR_VM_HSAVE_PA: msr_info->data = svm->nested.hsave_msr; @@ -3239,6 +3239,38 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr) vmcb_mark_dirty(svm->vmcb, VMCB_LBR); svm_update_lbrv(vcpu); break; + case MSR_IA32_LASTBRANCHFROMIP: + if (!lbrv) + return KVM_MSR_RET_UNSUPPORTED; + if (!msr->host_initiated) + return 1; + svm->vmcb->save.br_from = data; + vmcb_mark_dirty(svm->vmcb, VMCB_LBR); + break; + case MSR_IA32_LASTBRANCHTOIP: + if (!lbrv) + return KVM_MSR_RET_UNSUPPORTED; + if (!msr->host_initiated) + return 1; + svm->vmcb->save.br_to = data; + vmcb_mark_dirty(svm->vmcb, VMCB_LBR); + break; + case MSR_IA32_LASTINTFROMIP: + if (!lbrv) + return KVM_MSR_RET_UNSUPPORTED; + if (!msr->host_initiated) + return 1; + svm->vmcb->save.last_excp_from = data; + vmcb_mark_dirty(svm->vmcb, VMCB_LBR); + break; + case MSR_IA32_LASTINTTOIP: + if (!lbrv) + return KVM_MSR_RET_UNSUPPORTED; + if (!msr->host_initiated) + return 1; + svm->vmcb->save.last_excp_to = data; + vmcb_mark_dirty(svm->vmcb, VMCB_LBR); + break; case MSR_VM_HSAVE_PA: /* * Old kernels did not validate the value written to diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index b6c46697b023..8fbaa4216260 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1524,6 +1524,9 @@ static const u32 msrs_to_save_base[] = { MSR_IA32_UMWAIT_CONTROL, MSR_IA32_XFD, MSR_IA32_XFD_ERR, + MSR_IA32_DEBUGCTLMSR, + MSR_IA32_LASTBRANCHFROMIP, MSR_IA32_LASTBRANCHTOIP, + MSR_IA32_LASTINTFROMIP, MSR_IA32_LASTINTTOIP, }; static const u32 msrs_to_save_pmu[] = { -- 2.34.1