[Xen-devel] [PATCH] viridian: make viridian_time_domain_freeze() safe to call...

[Paul Durrant <paul.durrant@citrix.com>]

...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>
---
Cc: Jan Beulich <jbeulich@suse.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Wei Liu <wl@xen.org>
Cc: "Roger Pau Monné" <roger.pau@citrix.com>
---
 xen/arch/x86/hvm/viridian/time.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/hvm/viridian/time.c b/xen/arch/x86/hvm/viridian/time.c
index ac087383c8..e80330a6ae 100644
--- 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 viridian_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 viridian_time_vcpu_thaw(struct vcpu *v)
 {
     struct viridian_vcpu *vv = v->arch.hvm.viridian;
     unsigned int i;
@@ -336,7 +336,7 @@ 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 )
@@ -349,7 +349,7 @@ 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);
-- 
2.20.1.2.gb21ebb671


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