Re: [PATCH 6/6] KVM: x86: check DR6/7 high-bits are clear only on long-mode

Paolo Bonzini
2014-06-16T10:17:35Z

Il 15/06/2014 15:13, Nadav Amit ha scritto:
> From: Nadav Amit <nadav.amit@gmail.com>
>
> When the guest sets DR6 and DR7, KVM asserts the high 32-bits are clear, and
> otherwise injects a #GP exception. This exception should only be injected only
> if running in long-mode.
>
> Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
> ---
> arch/x86/kvm/x86.c | 13 +++++++++++--
> 1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 57eac30..71fe841 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -756,6 +756,15 @@ static void kvm_update_dr7(struct kvm_vcpu *vcpu)
> vcpu->arch.switch_db_regs |= KVM_DEBUGREG_BP_ENABLED;
> }
>
> +static bool is_64_bit_mode(struct kvm_vcpu *vcpu)
> +{
> + int cs_db, cs_l;
> + if (!is_long_mode(vcpu))
> + return false;
> + kvm_x86_ops->get_cs_db_l_bits(vcpu, &cs_db, &cs_l);
> + return cs_l;
> +}
> +
> static int __kvm_set_dr(struct kvm_vcpu *vcpu, int dr, unsigned long val)
> {
> switch (dr) {
> @@ -769,7 +778,7 @@ static int __kvm_set_dr(struct kvm_vcpu *vcpu, int dr, unsigned long val)
> return 1; /* #UD */
> /* fall through */
> case 6:
> - if (val & 0xffffffff00000000ULL)
> + if ((val & 0xffffffff00000000ULL) && is_64_bit_mode(vcpu))
> return -1; /* #GP */
> vcpu->arch.dr6 = (val & DR6_VOLATILE) | DR6_FIXED_1;
> kvm_update_dr6(vcpu);
> @@ -779,7 +788,7 @@ static int __kvm_set_dr(struct kvm_vcpu *vcpu, int dr, unsigned long val)
> return 1; /* #UD */
> /* fall through */
> default: /* 7 */
> - if (val & 0xffffffff00000000ULL)
> + if ((val & 0xffffffff00000000ULL) && is_64_bit_mode(vcpu))
> return -1; /* #GP */
> vcpu->arch.dr7 = (val & DR7_VOLATILE) | DR7_FIXED_1;
> kvm_update_dr7(vcpu);
>

Do you get this if the input register has bit 31 set?

Paolo