[PATCH v3 04/10] KVM: x86: Honor KVM_GUESTDBG_USE_HW_BP when emulating MOV DR (in emulator)

[Sean Christopherson]

From: Hou Wenlong <houwenlong.hwl@xxxxxxxxxxxx>

When emulating a MOV DR instruction, honor KVM_GUESTDBG_USE_HW_BP when
checking DR7.GD, and if there is a general-detect #DB, route it to host
userspace as appropriate.  Consulting only the guest's actual DR7 causes
KVM to fail to report a DR access to userspace (assuming the guest itself
doesn't have DR7.GD=1).

Fixes: ae675ef01cd8 ("KVM: x86: Wire-up hardware breakpoints for guest debugging")
Suggested-by: Lai Jiangshan <jiangshan.ljs@xxxxxxxxxxxx>
Signed-off-by: Hou Wenlong <houwenlong.hwl@xxxxxxxxxxxx>
[sean: only expose effective DR7 to emulator, massage changelog]
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/x86/kvm/emulate.c     |  2 +-
 arch/x86/kvm/kvm_emulate.h |  1 +
 arch/x86/kvm/x86.c         | 41 ++++++++++++++++++++++++++++++--------
 3 files changed, 35 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 510244555a74..917a521c299f 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -3848,7 +3848,7 @@ static int check_dr_read(struct x86_emulate_ctxt *ctxt)
 	if ((cr4 & X86_CR4_DE) && (dr == 4 || dr == 5))
 		return emulate_ud(ctxt);
 
-	if (ctxt->ops->get_dr(ctxt, 7) & DR7_GD)
+	if (ctxt->ops->get_eff_dr7(ctxt) & DR7_GD)
 		return emulate_db(ctxt, DR6_BD);
 
 	return X86EMUL_CONTINUE;
diff --git a/arch/x86/kvm/kvm_emulate.h b/arch/x86/kvm/kvm_emulate.h
index bb2a2aee0e13..33bfc9aa948e 100644
--- a/arch/x86/kvm/kvm_emulate.h
+++ b/arch/x86/kvm/kvm_emulate.h
@@ -215,6 +215,7 @@ struct x86_emulate_ops {
 	ulong (*get_cr)(struct x86_emulate_ctxt *ctxt, int cr);
 	int (*set_cr)(struct x86_emulate_ctxt *ctxt, int cr, ulong val);
 	int (*cpl)(struct x86_emulate_ctxt *ctxt);
+	ulong (*get_eff_dr7)(struct x86_emulate_ctxt *ctxt);
 	ulong (*get_dr)(struct x86_emulate_ctxt *ctxt, int dr);
 	int (*set_dr)(struct x86_emulate_ctxt *ctxt, int dr, ulong value);
 	int (*set_msr_with_filter)(struct x86_emulate_ctxt *ctxt, u32 msr_index, u64 data);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8a862d39302c..8b07bd2f8310 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1601,6 +1601,14 @@ unsigned long kvm_get_dr(struct kvm_vcpu *vcpu, int dr)
 }
 EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_get_dr);
 
+static unsigned long kvm_get_eff_dr7(struct kvm_vcpu *vcpu)
+{
+	if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP)
+		return vcpu->arch.guest_debug_dr7;
+
+	return vcpu->arch.dr7;
+}
+
 int kvm_emulate_rdpmc(struct kvm_vcpu *vcpu)
 {
 	u32 pmc = kvm_rcx_read(vcpu);
@@ -8548,6 +8556,11 @@ static void emulator_wbinvd(struct x86_emulate_ctxt *ctxt)
 	kvm_emulate_wbinvd_noskip(emul_to_vcpu(ctxt));
 }
 
+static unsigned long emulator_get_eff_dr7(struct x86_emulate_ctxt *ctxt)
+{
+	return kvm_get_eff_dr7(emul_to_vcpu(ctxt));
+}
+
 static unsigned long emulator_get_dr(struct x86_emulate_ctxt *ctxt, int dr)
 {
 	return kvm_get_dr(emul_to_vcpu(ctxt), dr);
@@ -8930,6 +8943,7 @@ static const struct x86_emulate_ops emulate_ops = {
 	.get_cr              = emulator_get_cr,
 	.set_cr              = emulator_set_cr,
 	.cpl                 = emulator_get_cpl,
+	.get_eff_dr7         = emulator_get_eff_dr7,
 	.get_dr              = emulator_get_dr,
 	.set_dr              = emulator_set_dr,
 	.set_msr_with_filter = emulator_set_msr_with_filter,
@@ -8976,23 +8990,36 @@ static void toggle_interruptibility(struct kvm_vcpu *vcpu, u32 mask)
 	}
 }
 
-static void kvm_inject_emulated_db(struct kvm_vcpu *vcpu, unsigned long dr6)
+static int kvm_inject_emulated_db(struct kvm_vcpu *vcpu, unsigned long dr6)
 {
+	struct kvm_run *kvm_run = vcpu->run;
+
+	if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP) {
+		kvm_run->debug.arch.dr6 = dr6 | DR6_ACTIVE_LOW;
+		kvm_run->debug.arch.pc = kvm_get_linear_rip(vcpu);
+		kvm_run->debug.arch.exception = DB_VECTOR;
+		kvm_run->exit_reason = KVM_EXIT_DEBUG;
+		return 0;
+	}
+
 	kvm_queue_exception_p(vcpu, DB_VECTOR, dr6);
+	return 1;
 }
 
-static void inject_emulated_exception(struct kvm_vcpu *vcpu)
+static int inject_emulated_exception(struct kvm_vcpu *vcpu)
 {
 	struct x86_exception *ex = &vcpu->arch.emulate_ctxt->exception;
 
 	if (ex->vector == DB_VECTOR)
-		kvm_inject_emulated_db(vcpu, ex->dr6);
-	else if (ex->vector == PF_VECTOR)
+		return kvm_inject_emulated_db(vcpu, ex->dr6);
+
+	if (ex->vector == PF_VECTOR)
 		kvm_inject_emulated_page_fault(vcpu, ex);
 	else if (ex->error_code_valid)
 		kvm_queue_exception_e(vcpu, ex->vector, ex->error_code);
 	else
 		kvm_queue_exception(vcpu, ex->vector);
+	return 1;
 }
 
 static struct x86_emulate_ctxt *alloc_emulate_ctxt(struct kvm_vcpu *vcpu)
@@ -9501,8 +9528,7 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 				 */
 				WARN_ON_ONCE(ctxt->exception.vector == UD_VECTOR ||
 					     exception_type(ctxt->exception.vector) == EXCPT_TRAP);
-				inject_emulated_exception(vcpu);
-				return 1;
+				return inject_emulated_exception(vcpu);
 			}
 			return handle_emulation_failure(vcpu, emulation_type);
 		}
@@ -9597,8 +9623,7 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 	if (ctxt->have_exception) {
 		WARN_ON_ONCE(vcpu->mmio_needed && !vcpu->mmio_is_write);
 		vcpu->mmio_needed = false;
-		r = 1;
-		inject_emulated_exception(vcpu);
+		r = inject_emulated_exception(vcpu);
 	} else if (vcpu->arch.pio.count) {
 		if (!vcpu->arch.pio.in) {
 			/* FIXME: return into emulator if single-stepping.  */
-- 
2.54.0.563.g4f69b47b94-goog