On Thu, Aug 29, 2019 at 2:25 PM Krish Sadhukhan
<krish.sadhukhan@xxxxxxxxxx> wrote:
>
> According to section "Checks on Guest Control Registers, Debug Registers, and
> and MSRs" in Intel SDM vol 3C, the following checks are performed on vmentry
> of nested guests:
>
> If the "load debug controls" VM-entry control is 1, bits reserved in the
> IA32_DEBUGCTL MSR must be 0 in the field for that register. The first
> processors to support the virtual-machine extensions supported only the
> 1-setting of this control and thus performed this check unconditionally.
>
> Signed-off-by: Krish Sadhukhan <krish.sadhukhan@xxxxxxxxxx>
> Reviewed-by: Karl Heubaum <karl.heubaum@xxxxxxxxxx>
> ---
> arch/x86/kvm/vmx/nested.c | 4 ++++
> arch/x86/kvm/x86.h | 6 ++++++
> 2 files changed, 10 insertions(+)
>
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 46af3a5e9209..0b234e95e0ed 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -2677,6 +2677,10 @@ static int nested_vmx_check_guest_state(struct kvm_vcpu *vcpu,
> !nested_guest_cr4_valid(vcpu, vmcs12->guest_cr4))
> return -EINVAL;
>
> + if ((vmcs12->vm_entry_controls & VM_ENTRY_LOAD_DEBUG_CONTROLS) &&
> + !kvm_debugctl_valid(vmcs12->guest_ia32_debugctl))
> + return -EINVAL;
> +
> if ((vmcs12->vm_entry_controls & VM_ENTRY_LOAD_IA32_PAT) &&
> !kvm_pat_valid(vmcs12->guest_ia32_pat))
> return -EINVAL;
> diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
> index a470ff0868c5..28ba6d0c359f 100644
> --- a/arch/x86/kvm/x86.h
> +++ b/arch/x86/kvm/x86.h
> @@ -354,6 +354,12 @@ static inline bool kvm_pat_valid(u64 data)
> return (data | ((data & 0x0202020202020202ull) << 1)) == data;
> }
>
> +static inline bool kvm_debugctl_valid(u64 data)
> +{
> + /* Bits 2, 3, 4, 5, 13 and [31:16] are reserved */
> + return ((data & 0xFFFFFFFFFFFF203Cull) ? false : true);
> +}
This should actually be consistent with the constraints in kvm_set_msr_common:
case MSR_IA32_DEBUGCTLMSR:
if (!data) {
/* We support the non-activated case already */
break;
} else if (data & ~(DEBUGCTLMSR_LBR | DEBUGCTLMSR_BTF)) {
/* Values other than LBR and BTF are vendor-specific,
thus reserved and should throw a #GP */
return 1;
}
Also, as I said earlier...
I'd rather see this built on an interface like:
bool kvm_valid_msr_value(u32 msr_index, u64 value);
Strange that we allow IA32_DEBUGCTL.BTF, since kvm_vcpu_do_singlestep
ignores it. And vLBR still isn't a thing, is it?
It's a bit scary to me that we allow any architecturally legal
IA32_DEBUGCTL bits to be set today. There's probably a CVE in there
somewhere.
