KVM: x86/xen: Use kvm_read_guest_virt() instead of open-coding it badly

In particular, we shouldn't assume that being contiguous in guest virtual
address space means being contiguous in guest *physical* address space.

In dropping the manual calls to kvm_mmu_gva_to_gpa_system(), also drop
the srcu_read_lock() that was around them. All call sites are reached
from kvm_xen_hypercall() which is called from the handle_exit function
with the read lock already held.

       5363952 ("KVM: x86/xen: handle PV timers oneshot mode")
       1a65105 ("KVM: x86/xen: handle PV spinlocks slowpath")

Fixes: 2fd6df2 ("KVM: x86/xen: intercept EVTCHNOP_send from guests")
Signed-off-by: David Woodhouse <[email protected]>
Message-Id: <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>

arch/x86/kvm/xen.c

@@ -1184,30 +1184,22 @@ static bool wait_pending_event(struct kvm_vcpu *vcpu, int nr_ports,
 static bool kvm_xen_schedop_poll(struct kvm_vcpu *vcpu, bool longmode,
  u64 param, u64 *r)
 {
- int idx, i;
  struct sched_poll sched_poll;
  evtchn_port_t port, *ports;
- gpa_t gpa;
+ struct x86_exception e;
+ int i;
 
  if (!lapic_in_kernel(vcpu) ||
  !(vcpu->kvm->arch.xen_hvm_config.flags & KVM_XEN_HVM_CONFIG_EVTCHN_SEND))
  return false;
 
- idx = srcu_read_lock(&vcpu->kvm->srcu);
- gpa = kvm_mmu_gva_to_gpa_system(vcpu, param, NULL);
- srcu_read_unlock(&vcpu->kvm->srcu, idx);
- if (!gpa) {
- *r = -EFAULT;
- return true;
- }
-
  if (IS_ENABLED(CONFIG_64BIT) && !longmode) {
  struct compat_sched_poll sp32;
 
  /* Sanity check that the compat struct definition is correct */
  BUILD_BUG_ON(sizeof(sp32) != 16);
 
- if (kvm_vcpu_read_guest(vcpu, gpa, &sp32, sizeof(sp32))) {
+ if (kvm_read_guest_virt(vcpu, param, &sp32, sizeof(sp32), &e)) {
  *r = -EFAULT;
  return true;
  }
@@ -1221,8 +1213,8 @@ static bool kvm_xen_schedop_poll(struct kvm_vcpu *vcpu, bool longmode,
  sched_poll.nr_ports = sp32.nr_ports;
  sched_poll.timeout = sp32.timeout;
  } else {
- if (kvm_vcpu_read_guest(vcpu, gpa, &sched_poll,
- sizeof(sched_poll))) {
+ if (kvm_read_guest_virt(vcpu, param, &sched_poll,
+ sizeof(sched_poll), &e)) {
  *r = -EFAULT;
  return true;
  }
@@ -1244,18 +1236,13 @@ static bool kvm_xen_schedop_poll(struct kvm_vcpu *vcpu, bool longmode,
  } else
  ports = &port;
 
+ if (kvm_read_guest_virt(vcpu, (gva_t)sched_poll.ports, ports,
+ sched_poll.nr_ports * sizeof(*ports), &e)) {
+ *r = -EFAULT;
+ return true;
+ }
+
  for (i = 0; i < sched_poll.nr_ports; i++) {
- idx = srcu_read_lock(&vcpu->kvm->srcu);
- gpa = kvm_mmu_gva_to_gpa_system(vcpu,
- (gva_t)(sched_poll.ports + i),
- NULL);
- srcu_read_unlock(&vcpu->kvm->srcu, idx);
-
- if (!gpa || kvm_vcpu_read_guest(vcpu, gpa,
- &ports[i], sizeof(port))) {
- *r = -EFAULT;
- goto out;
- }
  if (ports[i] >= max_evtchn_port(vcpu->kvm)) {
  *r = -EINVAL;
  goto out;
@@ -1331,9 +1318,8 @@ static bool kvm_xen_hcall_vcpu_op(struct kvm_vcpu *vcpu, bool longmode, int cmd,
  int vcpu_id, u64 param, u64 *r)
 {
  struct vcpu_set_singleshot_timer oneshot;
+ struct x86_exception e;
  s64 delta;
- gpa_t gpa;
- int idx;
 
  if (!kvm_xen_timer_enabled(vcpu))
  return false;
@@ -1344,9 +1330,6 @@ static bool kvm_xen_hcall_vcpu_op(struct kvm_vcpu *vcpu, bool longmode, int cmd,
  *r = -EINVAL;
  return true;
  }
- idx = srcu_read_lock(&vcpu->kvm->srcu);
- gpa = kvm_mmu_gva_to_gpa_system(vcpu, param, NULL);
- srcu_read_unlock(&vcpu->kvm->srcu, idx);
 
  /*
  * The only difference for 32-bit compat is the 4 bytes of
@@ -1364,9 +1347,8 @@ static bool kvm_xen_hcall_vcpu_op(struct kvm_vcpu *vcpu, bool longmode, int cmd,
  BUILD_BUG_ON(sizeof_field(struct compat_vcpu_set_singleshot_timer, flags) !=
  sizeof_field(struct vcpu_set_singleshot_timer, flags));
 
- if (!gpa ||
- kvm_vcpu_read_guest(vcpu, gpa, &oneshot, longmode ? sizeof(oneshot) :
- sizeof(struct compat_vcpu_set_singleshot_timer))) {
+ if (kvm_read_guest_virt(vcpu, param, &oneshot, longmode ? sizeof(oneshot) :
+ sizeof(struct compat_vcpu_set_singleshot_timer), &e)) {
  *r = -EFAULT;
  return true;
  }
@@ -2003,14 +1985,12 @@ static bool kvm_xen_hcall_evtchn_send(struct kvm_vcpu *vcpu, u64 param, u64 *r)
 {
  struct evtchnfd *evtchnfd;
  struct evtchn_send send;
- gpa_t gpa;
- int idx;
+ struct x86_exception e;
 
- idx = srcu_read_lock(&vcpu->kvm->srcu);
- gpa = kvm_mmu_gva_to_gpa_system(vcpu, param, NULL);
- srcu_read_unlock(&vcpu->kvm->srcu, idx);
+ /* Sanity check: this structure is the same for 32-bit and 64-bit */
+ BUILD_BUG_ON(sizeof(send) != 4);
 
- if (!gpa || kvm_vcpu_read_guest(vcpu, gpa, &send, sizeof(send))) {
+ if (kvm_read_guest_virt(vcpu, param, &send, sizeof(send), &e)) {
  *r = -EFAULT;
  return true;
  }