On Thu, Dec 5, 2019 at 3:46 AM Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>
> On 04/12/19 22:40, Jim Mattson wrote:
> > According to the SDM, a VMWRITE in VMX non-root operation with an
> > invalid VMCS-link pointer results in VMfailInvalid before the validity
> > of the VMCS field in the secondary source operand is checked.
> >
> > Fixes: 6d894f498f5d1 ("KVM: nVMX: vmread/vmwrite: Use shadow vmcs12 if running L2")
> > Signed-off-by: Jim Mattson <jmattson@xxxxxxxxxx>
> > Cc: Liran Alon <liran.alon@xxxxxxxxxx>
> > ---
> > arch/x86/kvm/vmx/nested.c | 38 +++++++++++++++++++-------------------
> > 1 file changed, 19 insertions(+), 19 deletions(-)
>
> As Vitaly pointed out, the test must be split in two, like this:
Right. Odd that no kvm-unit-tests noticed.
> ---------------- 8< -----------------------
> From 3b9d87060e800ffae2bd19da94ede05018066c87 Mon Sep 17 00:00:00 2001
> From: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Date: Thu, 5 Dec 2019 12:39:07 +0100
> Subject: [PATCH] kvm: nVMX: VMWRITE checks VMCS-link pointer before VMCS field
>
> According to the SDM, a VMWRITE in VMX non-root operation with an
> invalid VMCS-link pointer results in VMfailInvalid before the validity
> of the VMCS field in the secondary source operand is checked.
>
> While cleaning up handle_vmwrite, make the code of handle_vmread look
> the same, too.
Okay.
> Fixes: 6d894f498f5d1 ("KVM: nVMX: vmread/vmwrite: Use shadow vmcs12 if running L2")
> Signed-off-by: Jim Mattson <jmattson@xxxxxxxxxx>
> Cc: Liran Alon <liran.alon@xxxxxxxxxx>
>
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 4aea7d304beb..c080a879b95d 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -4767,14 +4767,13 @@ static int handle_vmread(struct kvm_vcpu *vcpu)
> if (to_vmx(vcpu)->nested.current_vmptr == -1ull)
> return nested_vmx_failInvalid(vcpu);
>
> - if (!is_guest_mode(vcpu))
> - vmcs12 = get_vmcs12(vcpu);
> - else {
> + vmcs12 = get_vmcs12(vcpu);
> + if (is_guest_mode(vcpu)) {
> /*
> * When vmcs->vmcs_link_pointer is -1ull, any VMREAD
> * to shadowed-field sets the ALU flags for VMfailInvalid.
> */
> - if (get_vmcs12(vcpu)->vmcs_link_pointer == -1ull)
> + if (vmcs12->vmcs_link_pointer == -1ull)
> return nested_vmx_failInvalid(vcpu);
> vmcs12 = get_shadow_vmcs12(vcpu);
> }
> @@ -4878,8 +4877,19 @@ static int handle_vmwrite(struct kvm_vcpu *vcpu)
> }
> }
>
> + vmcs12 = get_vmcs12(vcpu);
> + if (is_guest_mode(vcpu)) {
> + /*
> + * When vmcs->vmcs_link_pointer is -1ull, any VMWRITE
> + * to shadowed-field sets the ALU flags for VMfailInvalid.
> + */
> + if (vmcs12->vmcs_link_pointer == -1ull)
> + return nested_vmx_failInvalid(vcpu);
> + vmcs12 = get_shadow_vmcs12(vcpu);
> + }
>
> field = kvm_register_readl(vcpu, (((vmx_instruction_info) >> 28) & 0xf));
> +
> /*
> * If the vCPU supports "VMWRITE to any supported field in the
> * VMCS," then the "read-only" fields are actually read/write.
> @@ -4889,24 +4899,12 @@ static int handle_vmwrite(struct kvm_vcpu *vcpu)
> return nested_vmx_failValid(vcpu,
> VMXERR_VMWRITE_READ_ONLY_VMCS_COMPONENT);
>
> - if (!is_guest_mode(vcpu)) {
> - vmcs12 = get_vmcs12(vcpu);
> -
> - /*
> - * Ensure vmcs12 is up-to-date before any VMWRITE that dirties
> - * vmcs12, else we may crush a field or consume a stale value.
> - */
> - if (!is_shadow_field_rw(field))
> - copy_vmcs02_to_vmcs12_rare(vcpu, vmcs12);
> - } else {
> - /*
> - * When vmcs->vmcs_link_pointer is -1ull, any VMWRITE
> - * to shadowed-field sets the ALU flags for VMfailInvalid.
> - */
> - if (get_vmcs12(vcpu)->vmcs_link_pointer == -1ull)
> - return nested_vmx_failInvalid(vcpu);
> - vmcs12 = get_shadow_vmcs12(vcpu);
> - }
> + /*
> + * Ensure vmcs12 is up-to-date before any VMWRITE that dirties
> + * vmcs12, else we may crush a field or consume a stale value.
> + */
> + if (!is_guest_mode(vcpu) && !is_shadow_field_rw(field))
> + copy_vmcs02_to_vmcs12_rare(vcpu, vmcs12);
>
> offset = vmcs_field_to_offset(field);
> if (offset < 0)
>
>
> ... and also, do you have a matching kvm-unit-tests patch?
I'll put one together, along with a test that shows the current
priority inversion between read-only and unsupported VMCS fields.
> Thanks,
>
> Paolo
>
