viridian: make viridian_time_domain_freeze() safe to call...

...on a partially destroyed domain.

viridian_time_domain_freeze() and viridian_time_vcpu_freeze() rely
(respectively) on the dynamically allocated per-domain and per-vcpu viridian
areas [1], which are freed during domain_relinquish_resources().
Because arch_domain_pause() can call viridian_domain_time_freeze() this
can lead to host crashes if e.g. a XEN_DOMCTL_pausedomain is issued after
domain_relinquish_resources() has run.

To prevent such crashes, this patch adds a check of is_dying into
viridian_time_domain_freeze(), and viridian_time_domain_thaw() which is
similarly vulnerable to indirection into freed memory.

NOTE: The patch also makes viridian_time_vcpu_freeze/thaw() static, since
      they have no callers outside of the same source module.

[1] See commit e7a9b5e72f26 "viridian: separately allocate domain and vcpu
    structures".

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>

diff --git a/xen/arch/x86/hvm/viridian/time.c b/xen/arch/x86/hvm/viridian/time.c
index ac087383c8c16e988de8e9870cab7aa88bf5edd2..6ddca29b296ea947666e4b48dda9856d4bcde212 100644 (file)
--- a/xen/arch/x86/hvm/viridian/time.c
+++ b/xen/arch/x86/hvm/viridian/time.c
@@ -296,7 +296,7 @@ void viridian_time_poll_timers(struct vcpu *v)
         poll_stimer(v, i);
 }
 
-void viridian_time_vcpu_freeze(struct vcpu *v)
+static void time_vcpu_freeze(struct vcpu *v)
 {
     struct viridian_vcpu *vv = v->arch.hvm.viridian;
     unsigned int i;
@@ -314,7 +314,7 @@ void viridian_time_vcpu_freeze(struct vcpu *v)
     }
 }
 
-void viridian_time_vcpu_thaw(struct vcpu *v)
+static void time_vcpu_thaw(struct vcpu *v)
 {
     struct viridian_vcpu *vv = v->arch.hvm.viridian;
     unsigned int i;
@@ -336,11 +336,11 @@ void viridian_time_domain_freeze(const struct domain *d)
 {
     struct vcpu *v;
 
-    if ( !is_viridian_domain(d) )
+    if ( d->is_dying || !is_viridian_domain(d) )
         return;
 
     for_each_vcpu ( d, v )
-        viridian_time_vcpu_freeze(v);
+        time_vcpu_freeze(v);
 
     time_ref_count_freeze(d);
 }
@@ -349,13 +349,13 @@ void viridian_time_domain_thaw(const struct domain *d)
 {
     struct vcpu *v;
 
-    if ( !is_viridian_domain(d) )
+    if ( d->is_dying || !is_viridian_domain(d) )
         return;
 
     time_ref_count_thaw(d);
 
     for_each_vcpu ( d, v )
-        viridian_time_vcpu_thaw(v);
+        time_vcpu_thaw(v);
 }
 
 int viridian_time_wrmsr(struct vcpu *v, uint32_t idx, uint64_t val)