KVM: s390: protvirt: Only sync fmt4 registers

A lot of the registers are controlled by the Ultravisor and never
visible to KVM. Also some registers are overlayed, like gbea is with
sidad, which might leak data to userspace.

Hence we sync a minimal set of registers for both SIE formats and then
check and sync format 2 registers if necessary.
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
[borntraeger@de.ibm.com: patch merging, splitting, fixing]
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

arch/s390/kvm/kvm-s390.c

@@ -4113,7 +4113,7 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
 	return rc;
 }
 
-static void sync_regs(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
+static void sync_regs_fmt2(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 {
 	struct runtime_instr_cb *riccb;
 	struct gs_cb *gscb;
@@ -4122,16 +4122,7 @@ static void sync_regs(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 	gscb = (struct gs_cb *) &kvm_run->s.regs.gscb;
 	vcpu->arch.sie_block->gpsw.mask = kvm_run->psw_mask;
 	vcpu->arch.sie_block->gpsw.addr = kvm_run->psw_addr;
-	if (kvm_run->kvm_dirty_regs & KVM_SYNC_PREFIX)
-		kvm_s390_set_prefix(vcpu, kvm_run->s.regs.prefix);
-	if (kvm_run->kvm_dirty_regs & KVM_SYNC_CRS) {
-		memcpy(&vcpu->arch.sie_block->gcr, &kvm_run->s.regs.crs, 128);
-		/* some control register changes require a tlb flush */
-		kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
-	}
 	if (kvm_run->kvm_dirty_regs & KVM_SYNC_ARCH0) {
-		kvm_s390_set_cpu_timer(vcpu, kvm_run->s.regs.cputm);
-		vcpu->arch.sie_block->ckc = kvm_run->s.regs.ckc;
 		vcpu->arch.sie_block->todpr = kvm_run->s.regs.todpr;
 		vcpu->arch.sie_block->pp = kvm_run->s.regs.pp;
 		vcpu->arch.sie_block->gbea = kvm_run->s.regs.gbea;
@@ -4172,6 +4163,36 @@ static void sync_regs(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 		vcpu->arch.sie_block->fpf &= ~FPF_BPBC;
 		vcpu->arch.sie_block->fpf |= kvm_run->s.regs.bpbc ? FPF_BPBC : 0;
 	}
+	if (MACHINE_HAS_GS) {
+		preempt_disable();
+		__ctl_set_bit(2, 4);
+		if (current->thread.gs_cb) {
+			vcpu->arch.host_gscb = current->thread.gs_cb;
+			save_gs_cb(vcpu->arch.host_gscb);
+		}
+		if (vcpu->arch.gs_enabled) {
+			current->thread.gs_cb = (struct gs_cb *)
+						&vcpu->run->s.regs.gscb;
+			restore_gs_cb(current->thread.gs_cb);
+		}
+		preempt_enable();
+	}
+	/* SIE will load etoken directly from SDNX and therefore kvm_run */
+}
+
+static void sync_regs(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
+{
+	if (kvm_run->kvm_dirty_regs & KVM_SYNC_PREFIX)
+		kvm_s390_set_prefix(vcpu, kvm_run->s.regs.prefix);
+	if (kvm_run->kvm_dirty_regs & KVM_SYNC_CRS) {
+		memcpy(&vcpu->arch.sie_block->gcr, &kvm_run->s.regs.crs, 128);
+		/* some control register changes require a tlb flush */
+		kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
+	}
+	if (kvm_run->kvm_dirty_regs & KVM_SYNC_ARCH0) {
+		kvm_s390_set_cpu_timer(vcpu, kvm_run->s.regs.cputm);
+		vcpu->arch.sie_block->ckc = kvm_run->s.regs.ckc;
+	}
 	save_access_regs(vcpu->arch.host_acrs);
 	restore_access_regs(vcpu->run->s.regs.acrs);
 	/* save host (userspace) fprs/vrs */
@@ -4186,23 +4207,47 @@ static void sync_regs(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 	if (test_fp_ctl(current->thread.fpu.fpc))
 		/* User space provided an invalid FPC, let's clear it */
 		current->thread.fpu.fpc = 0;
+
+	/* Sync fmt2 only data */
+	if (likely(!kvm_s390_pv_cpu_is_protected(vcpu))) {
+		sync_regs_fmt2(vcpu, kvm_run);
+	} else {
+		/*
+		 * In several places we have to modify our internal view to
+		 * not do things that are disallowed by the ultravisor. For
+		 * example we must not inject interrupts after specific exits
+		 * (e.g. 112 prefix page not secure). We do this by turning
+		 * off the machine check, external and I/O interrupt bits
+		 * of our PSW copy. To avoid getting validity intercepts, we
+		 * do only accept the condition code from userspace.
+		 */
+		vcpu->arch.sie_block->gpsw.mask &= ~PSW_MASK_CC;
+		vcpu->arch.sie_block->gpsw.mask |= kvm_run->psw_mask &
+						   PSW_MASK_CC;
+	}
+
+	kvm_run->kvm_dirty_regs = 0;
+}
+
+static void store_regs_fmt2(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
+{
+	kvm_run->s.regs.todpr = vcpu->arch.sie_block->todpr;
+	kvm_run->s.regs.pp = vcpu->arch.sie_block->pp;
+	kvm_run->s.regs.gbea = vcpu->arch.sie_block->gbea;
+	kvm_run->s.regs.bpbc = (vcpu->arch.sie_block->fpf & FPF_BPBC) == FPF_BPBC;
 	if (MACHINE_HAS_GS) {
-		preempt_disable();
 		__ctl_set_bit(2, 4);
-		if (current->thread.gs_cb) {
-			vcpu->arch.host_gscb = current->thread.gs_cb;
-			save_gs_cb(vcpu->arch.host_gscb);
-		}
-		if (vcpu->arch.gs_enabled) {
-			current->thread.gs_cb = (struct gs_cb *)
-						&vcpu->run->s.regs.gscb;
-			restore_gs_cb(current->thread.gs_cb);
-		}
+		if (vcpu->arch.gs_enabled)
+			save_gs_cb(current->thread.gs_cb);
+		preempt_disable();
+		current->thread.gs_cb = vcpu->arch.host_gscb;
+		restore_gs_cb(vcpu->arch.host_gscb);
 		preempt_enable();
+		if (!vcpu->arch.host_gscb)
+			__ctl_clear_bit(2, 4);
+		vcpu->arch.host_gscb = NULL;
 	}
-	/* SIE will load etoken directly from SDNX and therefore kvm_run */
-
-	kvm_run->kvm_dirty_regs = 0;
+	/* SIE will save etoken directly into SDNX and therefore kvm_run */
 }
 
 static void store_regs(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
@@ -4213,13 +4258,9 @@ static void store_regs(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 	memcpy(&kvm_run->s.regs.crs, &vcpu->arch.sie_block->gcr, 128);
 	kvm_run->s.regs.cputm = kvm_s390_get_cpu_timer(vcpu);
 	kvm_run->s.regs.ckc = vcpu->arch.sie_block->ckc;
-	kvm_run->s.regs.todpr = vcpu->arch.sie_block->todpr;
-	kvm_run->s.regs.pp = vcpu->arch.sie_block->pp;
-	kvm_run->s.regs.gbea = vcpu->arch.sie_block->gbea;
 	kvm_run->s.regs.pft = vcpu->arch.pfault_token;
 	kvm_run->s.regs.pfs = vcpu->arch.pfault_select;
 	kvm_run->s.regs.pfc = vcpu->arch.pfault_compare;
-	kvm_run->s.regs.bpbc = (vcpu->arch.sie_block->fpf & FPF_BPBC) == FPF_BPBC;
 	save_access_regs(vcpu->run->s.regs.acrs);
 	restore_access_regs(vcpu->arch.host_acrs);
 	/* Save guest register state */
@@ -4228,19 +4269,8 @@ static void store_regs(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 	/* Restore will be done lazily at return */
 	current->thread.fpu.fpc = vcpu->arch.host_fpregs.fpc;
 	current->thread.fpu.regs = vcpu->arch.host_fpregs.regs;
-	if (MACHINE_HAS_GS) {
-		__ctl_set_bit(2, 4);
-		if (vcpu->arch.gs_enabled)
-			save_gs_cb(current->thread.gs_cb);
-		preempt_disable();
-		current->thread.gs_cb = vcpu->arch.host_gscb;
-		restore_gs_cb(vcpu->arch.host_gscb);
-		preempt_enable();
-		if (!vcpu->arch.host_gscb)
-			__ctl_clear_bit(2, 4);
-		vcpu->arch.host_gscb = NULL;
-	}
-	/* SIE will save etoken directly into SDNX and therefore kvm_run */
+	if (likely(!kvm_s390_pv_cpu_is_protected(vcpu)))
+		store_regs_fmt2(vcpu, kvm_run);
 }
 
 int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)