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

[Nadav Amit]

From: Nadav Amit <nadav.amit@xxxxxxxxx>

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@xxxxxxxxxxxxxxxxx>
---
 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

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