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-rw-r--r--main/xen/xsa228-4.8.patch198
1 files changed, 198 insertions, 0 deletions
diff --git a/main/xen/xsa228-4.8.patch b/main/xen/xsa228-4.8.patch
new file mode 100644
index 0000000000..57e6661cdb
--- /dev/null
+++ b/main/xen/xsa228-4.8.patch
@@ -0,0 +1,198 @@
+From cb91f4c43bd4158daa6561c73921a6455176f278 Mon Sep 17 00:00:00 2001
+From: Jan Beulich <jbeulich@suse.com>
+Date: Mon, 31 Jul 2017 15:17:56 +0100
+Subject: [PATCH] gnttab: split maptrack lock to make it fulfill its purpose
+ again
+
+The way the lock is currently being used in get_maptrack_handle(), it
+protects only the maptrack limit: The function acts on current's list
+only, so races on list accesses are impossible even without the lock.
+
+Otoh list access races are possible between __get_maptrack_handle() and
+put_maptrack_handle(), due to the invocation of the former for other
+than current from steal_maptrack_handle(). Introduce a per-vCPU lock
+for list accesses to become race free again. This lock will be
+uncontended except when it becomes necessary to take the steal path,
+i.e. in the common case there should be no meaningful performance
+impact.
+
+When in get_maptrack_handle adds a stolen entry to a fresh, empty,
+freelist, we think that there is probably no concurrency. However,
+this is not a fast path and adding the locking there makes the code
+clearly correct.
+
+Also, while we are here: the stolen maptrack_entry's tail pointer was
+not properly set. Set it.
+
+This is XSA-228.
+
+Reported-by: Ian Jackson <ian.jackson@eu.citrix.com>
+Signed-off-by: Jan Beulich <jbeulich@suse.com>
+Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>
+---
+ docs/misc/grant-tables.txt | 7 ++++++-
+ xen/common/grant_table.c | 30 ++++++++++++++++++++++++------
+ xen/include/xen/grant_table.h | 2 +-
+ xen/include/xen/sched.h | 1 +
+ 4 files changed, 32 insertions(+), 8 deletions(-)
+
+diff --git a/docs/misc/grant-tables.txt b/docs/misc/grant-tables.txt
+index 417ce2d..64da5cf 100644
+--- a/docs/misc/grant-tables.txt
++++ b/docs/misc/grant-tables.txt
+@@ -87,7 +87,8 @@ is complete.
+ inconsistent grant table state such as current
+ version, partially initialized active table pages,
+ etc.
+- grant_table->maptrack_lock : spinlock used to protect the maptrack free list
++ grant_table->maptrack_lock : spinlock used to protect the maptrack limit
++ v->maptrack_freelist_lock : spinlock used to protect the maptrack free list
+ active_grant_entry->lock : spinlock used to serialize modifications to
+ active entries
+
+@@ -102,6 +103,10 @@ is complete.
+ The maptrack free list is protected by its own spinlock. The maptrack
+ lock may be locked while holding the grant table lock.
+
++ The maptrack_freelist_lock is an innermost lock. It may be locked
++ while holding other locks, but no other locks may be acquired within
++ it.
++
+ Active entries are obtained by calling active_entry_acquire(gt, ref).
+ This function returns a pointer to the active entry after locking its
+ spinlock. The caller must hold the grant table read lock before
+diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c
+index f9654f1..593121c 100644
+--- a/xen/common/grant_table.c
++++ b/xen/common/grant_table.c
+@@ -304,11 +304,16 @@ __get_maptrack_handle(
+ {
+ unsigned int head, next, prev_head;
+
++ spin_lock(&v->maptrack_freelist_lock);
++
+ do {
+ /* No maptrack pages allocated for this VCPU yet? */
+ head = read_atomic(&v->maptrack_head);
+ if ( unlikely(head == MAPTRACK_TAIL) )
++ {
++ spin_unlock(&v->maptrack_freelist_lock);
+ return -1;
++ }
+
+ /*
+ * Always keep one entry in the free list to make it easier to
+@@ -316,12 +321,17 @@ __get_maptrack_handle(
+ */
+ next = read_atomic(&maptrack_entry(t, head).ref);
+ if ( unlikely(next == MAPTRACK_TAIL) )
++ {
++ spin_unlock(&v->maptrack_freelist_lock);
+ return -1;
++ }
+
+ prev_head = head;
+ head = cmpxchg(&v->maptrack_head, prev_head, next);
+ } while ( head != prev_head );
+
++ spin_unlock(&v->maptrack_freelist_lock);
++
+ return head;
+ }
+
+@@ -380,6 +390,8 @@ put_maptrack_handle(
+ /* 2. Add entry to the tail of the list on the original VCPU. */
+ v = currd->vcpu[maptrack_entry(t, handle).vcpu];
+
++ spin_lock(&v->maptrack_freelist_lock);
++
+ cur_tail = read_atomic(&v->maptrack_tail);
+ do {
+ prev_tail = cur_tail;
+@@ -388,6 +400,8 @@ put_maptrack_handle(
+
+ /* 3. Update the old tail entry to point to the new entry. */
+ write_atomic(&maptrack_entry(t, prev_tail).ref, handle);
++
++ spin_unlock(&v->maptrack_freelist_lock);
+ }
+
+ static inline int
+@@ -411,10 +425,6 @@ get_maptrack_handle(
+ */
+ if ( nr_maptrack_frames(lgt) >= max_maptrack_frames )
+ {
+- /*
+- * Can drop the lock since no other VCPU can be adding a new
+- * frame once they've run out.
+- */
+ spin_unlock(&lgt->maptrack_lock);
+
+ /*
+@@ -426,8 +436,12 @@ get_maptrack_handle(
+ handle = steal_maptrack_handle(lgt, curr);
+ if ( handle == -1 )
+ return -1;
++ spin_lock(&curr->maptrack_freelist_lock);
++ maptrack_entry(lgt, handle).ref = MAPTRACK_TAIL;
+ curr->maptrack_tail = handle;
+- write_atomic(&curr->maptrack_head, handle);
++ if ( curr->maptrack_head == MAPTRACK_TAIL )
++ write_atomic(&curr->maptrack_head, handle);
++ spin_unlock(&curr->maptrack_freelist_lock);
+ }
+ return steal_maptrack_handle(lgt, curr);
+ }
+@@ -460,12 +474,15 @@ get_maptrack_handle(
+ smp_wmb();
+ lgt->maptrack_limit += MAPTRACK_PER_PAGE;
+
++ spin_unlock(&lgt->maptrack_lock);
++ spin_lock(&curr->maptrack_freelist_lock);
++
+ do {
+ new_mt[i - 1].ref = read_atomic(&curr->maptrack_head);
+ head = cmpxchg(&curr->maptrack_head, new_mt[i - 1].ref, handle + 1);
+ } while ( head != new_mt[i - 1].ref );
+
+- spin_unlock(&lgt->maptrack_lock);
++ spin_unlock(&curr->maptrack_freelist_lock);
+
+ return handle;
+ }
+@@ -3474,6 +3491,7 @@ grant_table_destroy(
+
+ void grant_table_init_vcpu(struct vcpu *v)
+ {
++ spin_lock_init(&v->maptrack_freelist_lock);
+ v->maptrack_head = MAPTRACK_TAIL;
+ v->maptrack_tail = MAPTRACK_TAIL;
+ }
+diff --git a/xen/include/xen/grant_table.h b/xen/include/xen/grant_table.h
+index 4e77899..100f2b3 100644
+--- a/xen/include/xen/grant_table.h
++++ b/xen/include/xen/grant_table.h
+@@ -78,7 +78,7 @@ struct grant_table {
+ /* Mapping tracking table per vcpu. */
+ struct grant_mapping **maptrack;
+ unsigned int maptrack_limit;
+- /* Lock protecting the maptrack page list, head, and limit */
++ /* Lock protecting the maptrack limit */
+ spinlock_t maptrack_lock;
+ /* The defined versions are 1 and 2. Set to 0 if we don't know
+ what version to use yet. */
+diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
+index 1fbda87..ff0f38f 100644
+--- a/xen/include/xen/sched.h
++++ b/xen/include/xen/sched.h
+@@ -223,6 +223,7 @@ struct vcpu
+ int controller_pause_count;
+
+ /* Maptrack */
++ spinlock_t maptrack_freelist_lock;
+ unsigned int maptrack_head;
+ unsigned int maptrack_tail;
+
+--
+2.1.4
+