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

Nadav Amit
2014-06-15T13:13:02Z

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);
--
1.9.1