From: Sean Christopherson seanjc@google.com
commit c4abd7352023aa96114915a0bb2b88016a425cda upstream.
Stuff CR0 and/or CR4 to be compliant with a restricted guest if and only if KVM itself is not configured to utilize unrestricted guests, i.e. don't stuff CR0/CR4 for a restricted L2 that is running as the guest of an unrestricted L1. Any attempt to VM-Enter a restricted guest with invalid CR0/CR4 values should fail, i.e. in a nested scenario, KVM (as L0) should never observe a restricted L2 with incompatible CR0/CR4, since nested VM-Enter from L1 should have failed.
And if KVM does observe an active, restricted L2 with incompatible state, e.g. due to a KVM bug, fudging CR0/CR4 instead of letting VM-Enter fail does more harm than good, as KVM will often neglect to undo the side effects, e.g. won't clear rmode.vm86_active on nested VM-Exit, and thus the damage can easily spill over to L1. On the other hand, letting VM-Enter fail due to bad guest state is more likely to contain the damage to L2 as KVM relies on hardware to perform most guest state consistency checks, i.e. KVM needs to be able to reflect a failed nested VM-Enter into L1 irrespective of (un)restricted guest behavior.
Cc: Jim Mattson jmattson@google.com Cc: stable@vger.kernel.org Fixes: bddd82d19e2e ("KVM: nVMX: KVM needs to unset "unrestricted guest" VM-execution control in vmcs02 if vmcs12 doesn't set it") Signed-off-by: Sean Christopherson seanjc@google.com Message-Id: 20230613203037.1968489-3-seanjc@google.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kvm/vmx/vmx.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-)
--- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -1503,6 +1503,11 @@ void vmx_set_rflags(struct kvm_vcpu *vcp struct vcpu_vmx *vmx = to_vmx(vcpu); unsigned long old_rflags;
+ /* + * Unlike CR0 and CR4, RFLAGS handling requires checking if the vCPU + * is an unrestricted guest in order to mark L2 as needing emulation + * if L1 runs L2 as a restricted guest. + */ if (is_unrestricted_guest(vcpu)) { kvm_register_mark_available(vcpu, VCPU_EXREG_RFLAGS); vmx->rflags = rflags; @@ -3238,7 +3243,7 @@ void vmx_set_cr0(struct kvm_vcpu *vcpu, old_cr0_pg = kvm_read_cr0_bits(vcpu, X86_CR0_PG);
hw_cr0 = (cr0 & ~KVM_VM_CR0_ALWAYS_OFF); - if (is_unrestricted_guest(vcpu)) + if (enable_unrestricted_guest) hw_cr0 |= KVM_VM_CR0_ALWAYS_ON_UNRESTRICTED_GUEST; else { hw_cr0 |= KVM_VM_CR0_ALWAYS_ON; @@ -3266,7 +3271,7 @@ void vmx_set_cr0(struct kvm_vcpu *vcpu, } #endif
- if (enable_ept && !is_unrestricted_guest(vcpu)) { + if (enable_ept && !enable_unrestricted_guest) { /* * Ensure KVM has an up-to-date snapshot of the guest's CR3. If * the below code _enables_ CR3 exiting, vmx_cache_reg() will @@ -3397,7 +3402,7 @@ void vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long hw_cr4;
hw_cr4 = (cr4_read_shadow() & X86_CR4_MCE) | (cr4 & ~X86_CR4_MCE); - if (is_unrestricted_guest(vcpu)) + if (enable_unrestricted_guest) hw_cr4 |= KVM_VM_CR4_ALWAYS_ON_UNRESTRICTED_GUEST; else if (vmx->rmode.vm86_active) hw_cr4 |= KVM_RMODE_VM_CR4_ALWAYS_ON; @@ -3417,7 +3422,7 @@ void vmx_set_cr4(struct kvm_vcpu *vcpu, vcpu->arch.cr4 = cr4; kvm_register_mark_available(vcpu, VCPU_EXREG_CR4);
- if (!is_unrestricted_guest(vcpu)) { + if (!enable_unrestricted_guest) { if (enable_ept) { if (!is_paging(vcpu)) { hw_cr4 &= ~X86_CR4_PAE;