On Fri, Mar 10, 2023, Paolo Bonzini wrote:
> The effective values of the guest CR0 and CR4 registers may differ from
> those included in the VMCS12. In particular, disabling EPT forces
> CR4.PAE=1 and disabling unrestricted guest mode forces CR0.PG=CR0.PE=1.
>
> Therefore, checks on these bits cannot be delegated to the processor
> and must be performed by KVM.
>
> Reported-by: Reima ISHII <ishiir@xxxxxxxxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
> arch/x86/kvm/vmx/nested.c | 14 +++++++++++++-
> 1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index d93c715cda6a..43693e4772ff 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -3047,6 +3047,19 @@ static int nested_vmx_check_guest_state(struct kvm_vcpu *vcpu,
> vmcs12->guest_ia32_perf_global_ctrl)))
> return -EINVAL;
>
> + if (CC((vmcs12->guest_cr0 & (X86_CR0_PG | X86_CR0_PE)) == X86_CR0_PG))
> + return -EINVAL;
> +
> +#ifdef CONFIG_X86_64
The #ifdef isn't necessary, attempting to set for a 32-bit host should be rejected
by nested_vmx_check_controls() since nested_vmx_setup_ctls_msrs() clears the bit.
Ditto for the host logic related to VM_EXIT_HOST_ADDR_SPACE_SIZE, which looks
suspiciously similar ;-)
I'd rather delete the #ifdef in nested_vmx_check_host_state() and do something
similar here, e.g.
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 7c4f5ca405c7..3e367ec5086a 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -2903,7 +2903,7 @@ static int nested_vmx_check_address_space_size(struct kvm_vcpu *vcpu,
static int nested_vmx_check_host_state(struct kvm_vcpu *vcpu,
struct vmcs12 *vmcs12)
{
- bool ia32e;
+ bool ia32e = !!(vmcs12->vm_exit_controls & VM_EXIT_HOST_ADDR_SPACE_SIZE);
if (CC(!nested_host_cr0_valid(vcpu, vmcs12->host_cr0)) ||
CC(!nested_host_cr4_valid(vcpu, vmcs12->host_cr4)) ||
@@ -2923,12 +2923,6 @@ static int nested_vmx_check_host_state(struct kvm_vcpu *vcpu,
vmcs12->host_ia32_perf_global_ctrl)))
return -EINVAL;
-#ifdef CONFIG_X86_64
- ia32e = !!(vmcs12->vm_exit_controls & VM_EXIT_HOST_ADDR_SPACE_SIZE);
-#else
- ia32e = false;
-#endif
-
if (ia32e) {
if (CC(!(vmcs12->host_cr4 & X86_CR4_PAE)))
return -EINVAL;
> + ia32e = !!(vmcs12->vm_entry_controls & VM_ENTRY_IA32E_MODE);
> +#else
> + ia32e = false;
> +#endif
> + if (CC(ia32e &&
> + (!(vmcs12->guest_cr4 & X86_CR4_PAE) ||
> + !(vmcs12->guest_cr0 & X86_CR0_PG))))
> + return -EINVAL;
This is a lot easier to read IMO, and has the advantage of more precisely
identifying the failure in the tracepoint.
if (CC(ia32e && !(vmcs12->guest_cr4 & X86_CR4_PAE)) ||
CC(ia32e && !(vmcs12->guest_cr4 & X86_CR0_PG)))
return -EINVAL;
> +
> /*
> * If the load IA32_EFER VM-entry control is 1, the following checks
> * are performed on the field for the IA32_EFER MSR:
> @@ -3058,7 +3071,6 @@ static int nested_vmx_check_guest_state(struct kvm_vcpu *vcpu,
> */
> if (to_vmx(vcpu)->nested.nested_run_pending &&
> (vmcs12->vm_entry_controls & VM_ENTRY_LOAD_IA32_EFER)) {
> - ia32e = (vmcs12->vm_entry_controls & VM_ENTRY_IA32E_MODE) != 0;
> if (CC(!kvm_valid_efer(vcpu, vmcs12->guest_ia32_efer)) ||
> CC(ia32e != !!(vmcs12->guest_ia32_efer & EFER_LMA)) ||
> CC(((vmcs12->guest_cr0 & X86_CR0_PG) &&
> --
> 2.39.1
>
