KVM: x86: Breakpoints do not consider CS.base

x86 debug registers hold a linear address. Therefore, breakpoints detection
should consider CS.base, and check whether instruction linear address equals
(CS.base + RIP). This patch introduces a function to evaluate RIP linear
address and uses it for breakpoints detection.

Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -1067,6 +1067,7 @@ void kvm_arch_mmu_notifier_invalidate_page(struct kvm *kvm,
 void kvm_define_shared_msr(unsigned index, u32 msr);
 int kvm_set_shared_msr(unsigned index, u64 val, u64 mask);
 
+unsigned long kvm_get_linear_rip(struct kvm_vcpu *vcpu);
 bool kvm_is_linear_rip(struct kvm_vcpu *vcpu, unsigned long linear_rip);
 
 void kvm_arch_async_page_not_present(struct kvm_vcpu *vcpu,

arch/x86/kvm/vmx.c

@@ -5118,9 +5118,7 @@ static int handle_dr(struct kvm_vcpu *vcpu)
 		if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP) {
 			vcpu->run->debug.arch.dr6 = vcpu->arch.dr6;
 			vcpu->run->debug.arch.dr7 = dr7;
-			vcpu->run->debug.arch.pc =
-				vmcs_readl(GUEST_CS_BASE) +
-				vmcs_readl(GUEST_RIP);
+			vcpu->run->debug.arch.pc = kvm_get_linear_rip(vcpu);
 			vcpu->run->debug.arch.exception = DB_VECTOR;
 			vcpu->run->exit_reason = KVM_EXIT_DEBUG;
 			return 0;

arch/x86/kvm/x86.c

@@ -5207,21 +5207,17 @@ static void kvm_vcpu_check_singlestep(struct kvm_vcpu *vcpu, unsigned long rflag
 
 static bool kvm_vcpu_check_breakpoint(struct kvm_vcpu *vcpu, int *r)
 {
-	struct kvm_run *kvm_run = vcpu->run;
-	unsigned long eip = vcpu->arch.emulate_ctxt.eip;
-	u32 dr6 = 0;
-
 	if (unlikely(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP) &&
 	    (vcpu->arch.guest_debug_dr7 & DR7_BP_EN_MASK)) {
-		dr6 = kvm_vcpu_check_hw_bp(eip, 0,
+		struct kvm_run *kvm_run = vcpu->run;
+		unsigned long eip = kvm_get_linear_rip(vcpu);
+		u32 dr6 = kvm_vcpu_check_hw_bp(eip, 0,
 					   vcpu->arch.guest_debug_dr7,
 					   vcpu->arch.eff_db);
 
 		if (dr6 != 0) {
 			kvm_run->debug.arch.dr6 = dr6 | DR6_FIXED_1 | DR6_RTM;
-			kvm_run->debug.arch.pc = kvm_rip_read(vcpu) +
-				get_segment_base(vcpu, VCPU_SREG_CS);
-
+			kvm_run->debug.arch.pc = eip;
 			kvm_run->debug.arch.exception = DB_VECTOR;
 			kvm_run->exit_reason = KVM_EXIT_DEBUG;
 			*r = EMULATE_USER_EXIT;
@@ -5231,7 +5227,8 @@ static bool kvm_vcpu_check_breakpoint(struct kvm_vcpu *vcpu, int *r)
 
 	if (unlikely(vcpu->arch.dr7 & DR7_BP_EN_MASK) &&
 	    !(kvm_get_rflags(vcpu) & X86_EFLAGS_RF)) {
-		dr6 = kvm_vcpu_check_hw_bp(eip, 0,
+		unsigned long eip = kvm_get_linear_rip(vcpu);
+		u32 dr6 = kvm_vcpu_check_hw_bp(eip, 0,
 					   vcpu->arch.dr7,
 					   vcpu->arch.db);
 
@@ -7538,12 +7535,18 @@ int kvm_arch_interrupt_allowed(struct kvm_vcpu *vcpu)
 	return kvm_x86_ops->interrupt_allowed(vcpu);
 }
 
-bool kvm_is_linear_rip(struct kvm_vcpu *vcpu, unsigned long linear_rip)
+unsigned long kvm_get_linear_rip(struct kvm_vcpu *vcpu)
 {
-	unsigned long current_rip = kvm_rip_read(vcpu) +
-		get_segment_base(vcpu, VCPU_SREG_CS);
+	if (is_64_bit_mode(vcpu))
+		return kvm_rip_read(vcpu);
+	return (u32)(get_segment_base(vcpu, VCPU_SREG_CS) +
+		     kvm_rip_read(vcpu));
+}
+EXPORT_SYMBOL_GPL(kvm_get_linear_rip);
 
-	return current_rip == linear_rip;
+bool kvm_is_linear_rip(struct kvm_vcpu *vcpu, unsigned long linear_rip)
+{
+	return kvm_get_linear_rip(vcpu) == linear_rip;
 }
 EXPORT_SYMBOL_GPL(kvm_is_linear_rip);