KVM: x86: fix CR8 handling

The handling of CR8 writes in KVM is currently somewhat cumbersome.
This patch makes it look like the other CR register handlers
and fixes a possible issue in VMX, where the RIP would be incremented
despite an injected #GP.

Signed-off-by: Andre Przywara <andre.przywara@amd.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

4 files changed, 15 insertions, 16 deletions

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 4461429957a9..cb5cad2f2d46 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -661,7 +661,7 @@ int kvm_task_switch(struct kvm_vcpu *vcpu, u16 tss_selector, int reason,
 int kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0);
 int kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3);
 int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4);
-void kvm_set_cr8(struct kvm_vcpu *vcpu, unsigned long cr8);
+int kvm_set_cr8(struct kvm_vcpu *vcpu, unsigned long cr8);
 int kvm_set_dr(struct kvm_vcpu *vcpu, int dr, unsigned long val);
 int kvm_get_dr(struct kvm_vcpu *vcpu, int dr, unsigned long *val);
 unsigned long kvm_get_cr8(struct kvm_vcpu *vcpu);
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 73461b1cfb05..3d4b88af50f9 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -2676,16 +2676,17 @@ static int cr0_write_interception(struct vcpu_svm *svm)
 static int cr8_write_interception(struct vcpu_svm *svm)
 {
         struct kvm_run *kvm_run = svm->vcpu.run;
+        int r;
 
         u8 cr8_prev = kvm_get_cr8(&svm->vcpu);
         /* instruction emulation calls kvm_set_cr8() */
-        emulate_instruction(&svm->vcpu, 0, 0, 0);
+        r = emulate_instruction(&svm->vcpu, 0, 0, 0);
         if (irqchip_in_kernel(svm->vcpu.kvm)) {
                 clr_cr_intercept(svm, INTERCEPT_CR8_WRITE);
-                return 1;
+                return r == EMULATE_DONE;
         }
         if (cr8_prev <= kvm_get_cr8(&svm->vcpu))
-                return 1;
+                return r == EMULATE_DONE;
         kvm_run->exit_reason = KVM_EXIT_SET_TPR;
         return 0;
 }
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index c1952603d580..8e87bae09a7a 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3185,8 +3185,8 @@ static int handle_cr(struct kvm_vcpu *vcpu)
                 case 8: {
                                 u8 cr8_prev = kvm_get_cr8(vcpu);
                                 u8 cr8 = kvm_register_read(vcpu, reg);
-                                kvm_set_cr8(vcpu, cr8);
-                                skip_emulated_instruction(vcpu);
+                                err = kvm_set_cr8(vcpu, cr8);
+                                complete_insn_gp(vcpu, err);
                                 if (irqchip_in_kernel(vcpu->kvm))
                                         return 1;
                                 if (cr8_prev <= cr8)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index f569da8ff839..2dbf68cd46e3 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -662,7 +662,7 @@ int kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
 }
 EXPORT_SYMBOL_GPL(kvm_set_cr3);
 
-int __kvm_set_cr8(struct kvm_vcpu *vcpu, unsigned long cr8)
+int kvm_set_cr8(struct kvm_vcpu *vcpu, unsigned long cr8)
 {
         if (cr8 & CR8_RESERVED_BITS)
                 return 1;
@@ -672,12 +672,6 @@ int __kvm_set_cr8(struct kvm_vcpu *vcpu, unsigned long cr8)
                 vcpu->arch.cr8 = cr8;
         return 0;
 }
-
-void kvm_set_cr8(struct kvm_vcpu *vcpu, unsigned long cr8)
-{
-        if (__kvm_set_cr8(vcpu, cr8))
-                kvm_inject_gp(vcpu, 0);
-}
 EXPORT_SYMBOL_GPL(kvm_set_cr8);
 
 unsigned long kvm_get_cr8(struct kvm_vcpu *vcpu)
@@ -4104,7 +4098,7 @@ static int emulator_set_cr(int cr, unsigned long val, struct kvm_vcpu *vcpu)
                 res = kvm_set_cr4(vcpu, mk_cr_64(kvm_read_cr4(vcpu), val));
                 break;
         case 8:
-                res = __kvm_set_cr8(vcpu, val & 0xfUL);
+                res = kvm_set_cr8(vcpu, val);
                 break;
         default:
                 vcpu_printf(vcpu, "%s: unexpected cr %u\n", __func__, cr);
@@ -5381,8 +5375,12 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
         }
 
         /* re-sync apic's tpr */
-        if (!irqchip_in_kernel(vcpu->kvm))
-                kvm_set_cr8(vcpu, kvm_run->cr8);
+        if (!irqchip_in_kernel(vcpu->kvm)) {
+                if (kvm_set_cr8(vcpu, kvm_run->cr8) != 0) {
+                        r = -EINVAL;
+                        goto out;
+                }
+        }
 
         if (vcpu->arch.pio.count || vcpu->mmio_needed) {
                 if (vcpu->mmio_needed) {