[PATCH] xen/common: Avoid undefined behaviour by shifting into a sign bit

[Andrew Cooper <andrew.cooper3@citrix.com>]

For d->shutdown_code, change the field to being unsigned and using an unsigned
sentinel.  The sentinal needs to be distinguishable from any value
representable in a u8.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: George Dunlap <george.dunlap@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: George Dunlap <George.Dunlap@eu.citrix.com>
CC: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
CC: Stefano Stabellini <sstabellini@kernel.org>
CC: Tim Deegan <tim@xen.org>

v2:
 * Change d->shutdown_code to being unsigned.
---
 xen/common/domain.c       | 6 +++---
 xen/common/schedule.c     | 2 +-
 xen/common/xmalloc_tlsf.c | 4 ++--
 xen/include/xen/sched.h   | 5 +++--
 4 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/xen/common/domain.c b/xen/common/domain.c
index 339ee56..a8804e4 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -293,7 +293,7 @@ struct domain *domain_create(domid_t domid, unsigned int domcr_flags,
     d->auto_node_affinity = 1;
 
     spin_lock_init(&d->shutdown_lock);
-    d->shutdown_code = -1;
+    d->shutdown_code = SHUTDOWN_CODE_INVALID;
 
     spin_lock_init(&d->pbuf_lock);
 
@@ -695,7 +695,7 @@ void domain_shutdown(struct domain *d, u8 reason)
 
     spin_lock(&d->shutdown_lock);
 
-    if ( d->shutdown_code == -1 )
+    if ( d->shutdown_code == SHUTDOWN_CODE_INVALID )
         d->shutdown_code = reason;
     reason = d->shutdown_code;
 
@@ -742,7 +742,7 @@ void domain_resume(struct domain *d)
     spin_lock(&d->shutdown_lock);
 
     d->is_shutting_down = d->is_shut_down = 0;
-    d->shutdown_code = -1;
+    d->shutdown_code = SHUTDOWN_CODE_INVALID;
 
     for_each_vcpu ( d, v )
     {
diff --git a/xen/common/schedule.c b/xen/common/schedule.c
index 852f840..32a300f 100644
--- a/xen/common/schedule.c
+++ b/xen/common/schedule.c
@@ -1120,7 +1120,7 @@ ret_t do_sched_op(int cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
                  d->domain_id, current->vcpu_id, sched_shutdown.reason);
 
         spin_lock(&d->shutdown_lock);
-        if ( d->shutdown_code == -1 )
+        if ( d->shutdown_code == SHUTDOWN_CODE_INVALID )
             d->shutdown_code = (u8)sched_shutdown.reason;
         spin_unlock(&d->shutdown_lock);
 
diff --git a/xen/common/xmalloc_tlsf.c b/xen/common/xmalloc_tlsf.c
index b13317e..6c1b882 100644
--- a/xen/common/xmalloc_tlsf.c
+++ b/xen/common/xmalloc_tlsf.c
@@ -177,7 +177,7 @@ static inline void MAPPING_INSERT(unsigned long r, int *fl, int *sl)
 static inline struct bhdr *FIND_SUITABLE_BLOCK(struct xmem_pool *p, int *fl,
                                                int *sl)
 {
-    u32 tmp = p->sl_bitmap[*fl] & (~0 << *sl);
+    u32 tmp = p->sl_bitmap[*fl] & (~0u << *sl);
     struct bhdr *b = NULL;
 
     if ( tmp )
@@ -187,7 +187,7 @@ static inline struct bhdr *FIND_SUITABLE_BLOCK(struct xmem_pool *p, int *fl,
     }
     else
     {
-        *fl = ffs(p->fl_bitmap & (~0 << (*fl + 1))) - 1;
+        *fl = ffs(p->fl_bitmap & (~0u << (*fl + 1))) - 1;
         if ( likely(*fl > 0) )
         {
             *sl = ffs(p->sl_bitmap[*fl]) - 1;
diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index 888bc19..2f9c15f 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -404,7 +404,8 @@ struct domain
     spinlock_t       shutdown_lock;
     bool_t           is_shutting_down; /* in process of shutting down? */
     bool_t           is_shut_down;     /* fully shut down? */
-    int              shutdown_code;
+#define SHUTDOWN_CODE_INVALID ~0u
+    unsigned int     shutdown_code;
 
     /* If this is not 0, send suspend notification here instead of
      * raising DOM_EXC */
@@ -483,7 +484,7 @@ extern struct vcpu *idle_vcpu[NR_CPUS];
 #define is_idle_domain(d) ((d)->domain_id == DOMID_IDLE)
 #define is_idle_vcpu(v)   (is_idle_domain((v)->domain))
 
-#define DOMAIN_DESTROYED (1<<31) /* assumes atomic_t is >= 32 bits */
+#define DOMAIN_DESTROYED (1u << 31) /* assumes atomic_t is >= 32 bits */
 #define put_domain(_d) \
   if ( atomic_dec_and_test(&(_d)->refcnt) ) domain_destroy(_d)
 
-- 
2.1.4


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