From 56e7cadc78051e4dbff6ff9e3e57bbab720de20f Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Mon, 19 Apr 2021 09:28:22 +0000 Subject: [PATCH] KVM: SVM: load control fields from VMCB12 before checking them MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit stable inclusion from stable-5.10.28 commit 5f6625f5cd5c593fae05a6ce22b406166bc796b8 bugzilla: 51779 -------------------------------- commit a58d9166a756a0f4a6618e4f593232593d6df134 upstream. Avoid races between check and use of the nested VMCB controls. This for example ensures that the VMRUN intercept is always reflected to the nested hypervisor, instead of being processed by the host. Without this patch, it is possible to end up with svm->nested.hsave pointing to the MSR permission bitmap for nested guests. This bug is CVE-2021-29657. Reported-by: Felix Wilhelm Cc: stable@vger.kernel.org Fixes: 2fcf4876ada ("KVM: nSVM: implement on demand allocation of the nested state") Signed-off-by: Paolo Bonzini Signed-off-by: Greg Kroah-Hartman Signed-off-by: Chen Jun Acked-by:  Weilong Chen Signed-off-by: Zheng Zengkai --- arch/x86/kvm/svm/nested.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c index 1008cc6cb66c..dd318ca6c722 100644 --- a/arch/x86/kvm/svm/nested.c +++ b/arch/x86/kvm/svm/nested.c @@ -246,7 +246,7 @@ static bool nested_vmcb_check_controls(struct vmcb_control_area *control) return true; } -static bool nested_vmcb_checks(struct vcpu_svm *svm, struct vmcb *vmcb12) +static bool nested_vmcb_check_save(struct vcpu_svm *svm, struct vmcb *vmcb12) { struct kvm_vcpu *vcpu = &svm->vcpu; bool vmcb12_lma; @@ -271,7 +271,7 @@ static bool nested_vmcb_checks(struct vcpu_svm *svm, struct vmcb *vmcb12) if (kvm_valid_cr4(&svm->vcpu, vmcb12->save.cr4)) return false; - return nested_vmcb_check_controls(&vmcb12->control); + return true; } static void load_nested_vmcb_control(struct vcpu_svm *svm, @@ -454,7 +454,6 @@ int enter_svm_guest_mode(struct vcpu_svm *svm, u64 vmcb12_gpa, int ret; svm->nested.vmcb12_gpa = vmcb12_gpa; - load_nested_vmcb_control(svm, &vmcb12->control); nested_prepare_vmcb_save(svm, vmcb12); nested_prepare_vmcb_control(svm); @@ -501,7 +500,10 @@ int nested_svm_vmrun(struct vcpu_svm *svm) if (WARN_ON_ONCE(!svm->nested.initialized)) return -EINVAL; - if (!nested_vmcb_checks(svm, vmcb12)) { + load_nested_vmcb_control(svm, &vmcb12->control); + + if (!nested_vmcb_check_save(svm, vmcb12) || + !nested_vmcb_check_controls(&svm->nested.ctl)) { vmcb12->control.exit_code = SVM_EXIT_ERR; vmcb12->control.exit_code_hi = 0; vmcb12->control.exit_info_1 = 0; -- GitLab