diff options
| author | Paolo Bonzini <pbonzini@redhat.com> | 2021-03-31 06:28:01 -0400 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2021-04-01 05:11:35 -0400 |
| commit | 3c346c0c60ab06a021d1c0884a0ef494bc4ee3a7 (patch) | |
| tree | 860cb0fd3c84ff826ff267151bfe6c0bf17abd10 /arch | |
| parent | a58d9166a756a0f4a6618e4f593232593d6df134 (diff) | |
KVM: SVM: ensure that EFER.SVME is set when running nested guest or on nested vmexit
Fixing nested_vmcb_check_save to avoid all TOC/TOU races
is a bit harder in released kernels, so do the bare minimum
by avoiding that EFER.SVME is cleared. This is problematic
because svm_set_efer frees the data structures for nested
virtualization if EFER.SVME is cleared.
Also check that EFER.SVME remains set after a nested vmexit;
clearing it could happen if the bit is zero in the save area
that is passed to KVM_SET_NESTED_STATE (the save area of the
nested state corresponds to the nested hypervisor's state
and is restored on the next nested vmexit).
Cc: stable@vger.kernel.org
Fixes: 2fcf4876ada ("KVM: nSVM: implement on demand allocation of the nested state")
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/kvm/svm/nested.c | 18 |
1 files changed, 17 insertions, 1 deletions
diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c index 061a00f91af5..c9e7b86350d6 100644 --- a/arch/x86/kvm/svm/nested.c +++ b/arch/x86/kvm/svm/nested.c @@ -229,6 +229,13 @@ static bool nested_vmcb_check_save(struct vcpu_svm *svm, struct vmcb *vmcb12) { bool vmcb12_lma; + /* + * FIXME: these should be done after copying the fields, + * to avoid TOC/TOU races. For these save area checks + * the possible damage is limited since kvm_set_cr0 and + * kvm_set_cr4 handle failure; EFER_SVME is an exception + * so it is force-set later in nested_prepare_vmcb_save. + */ if ((vmcb12->save.efer & EFER_SVME) == 0) return false; @@ -382,7 +389,14 @@ static void nested_prepare_vmcb_save(struct vcpu_svm *svm, struct vmcb *vmcb12) svm->vmcb->save.gdtr = vmcb12->save.gdtr; svm->vmcb->save.idtr = vmcb12->save.idtr; kvm_set_rflags(&svm->vcpu, vmcb12->save.rflags); - svm_set_efer(&svm->vcpu, vmcb12->save.efer); + + /* + * Force-set EFER_SVME even though it is checked earlier on the + * VMCB12, because the guest can flip the bit between the check + * and now. Clearing EFER_SVME would call svm_free_nested. + */ + svm_set_efer(&svm->vcpu, vmcb12->save.efer | EFER_SVME); + svm_set_cr0(&svm->vcpu, vmcb12->save.cr0); svm_set_cr4(&svm->vcpu, vmcb12->save.cr4); svm->vmcb->save.cr2 = svm->vcpu.arch.cr2 = vmcb12->save.cr2; @@ -1188,6 +1202,8 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu, */ if (!(save->cr0 & X86_CR0_PG)) goto out_free; + if (!(save->efer & EFER_SVME)) + goto out_free; /* * All checks done, we can enter guest mode. L1 control fields |