Re: [PATCH 2/4] KVM: nVMX: Check GUEST_DR7 on vmentry of nested guests

[Jim Mattson <jmattson@google.com>]

On Thu, Aug 29, 2019 at 2:25 PM Krish Sadhukhan
<krish.sadhukhan@oracle.com> 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 63:32 in the DR7
>     field must be 0.
>
> Signed-off-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
> Reviewed-by: Karl Heubaum <karl.heubaum@oracle.com>
> ---
>  arch/x86/kvm/vmx/nested.c | 6 ++++++
>  arch/x86/kvm/x86.c        | 2 +-
>  arch/x86/kvm/x86.h        | 6 ++++++
>  3 files changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 0b234e95e0ed..f04619daf906 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -2681,6 +2681,12 @@ static int nested_vmx_check_guest_state(struct kvm_vcpu *vcpu,
>             !kvm_debugctl_valid(vmcs12->guest_ia32_debugctl))
>                 return -EINVAL;
>
> +#ifdef CONFIG_X86_64
> +       if ((vmcs12->vm_entry_controls & VM_ENTRY_LOAD_DEBUG_CONTROLS) &&
> +           !kvm_dr7_valid(vmcs12->guest_dr7))
> +               return -EINVAL;
> +#endif
> +
>         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.c b/arch/x86/kvm/x86.c
> index fafd81d2c9ea..423a7a573608 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1051,7 +1051,7 @@ static int __kvm_set_dr(struct kvm_vcpu *vcpu, int dr, unsigned long val)
>         case 5:
>                 /* fall through */
>         default: /* 7 */
> -               if (val & 0xffffffff00000000ULL)
> +               if (!kvm_dr7_valid(val))
>                         return -1; /* #GP */
>                 vcpu->arch.dr7 = (val & DR7_VOLATILE) | DR7_FIXED_1;
>                 kvm_update_dr7(vcpu);
> diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
> index 28ba6d0c359f..4e55851fc3fb 100644
> --- a/arch/x86/kvm/x86.h
> +++ b/arch/x86/kvm/x86.h
> @@ -360,6 +360,12 @@ static inline bool kvm_debugctl_valid(u64 data)
>         return ((data & 0xFFFFFFFFFFFF203Cull) ? false : true);
>  }
>
> +static inline bool kvm_dr7_valid(u64 data)

This should be 'unsigned long data.'

> +{
> +       /* Bits [63:32] are reserved */
> +       return ((data & 0xFFFFFFFF00000000ull) ? false : true);

    return !(data & 0xFFFFFFFF00000000ull);

Or, shorter:

    return (u32)data == data;

> +}
> +
>  void kvm_load_guest_xcr0(struct kvm_vcpu *vcpu);
>  void kvm_put_guest_xcr0(struct kvm_vcpu *vcpu);
>
> --
> 2.20.1
>