[PATCH] selinux: Reduce memory use by avtab

This patch improves memory use by SELinux by both reducing the avtab node
size and reducing the number of avtab nodes.  The memory savings are
substantial, e.g.  on a 64-bit system after boot, James Morris reported the
following data for the targeted and strict policies:

            #objs  objsize   kernmem
Targeted:
  Before:  237888       40     9.1MB
  After:    19968       24     468KB

Strict:
  Before:  571680       40   21.81MB
  After:   221052       24    5.06MB

The improvement in memory use comes at a cost in the speed of security
server computations of access vectors, but these computations are only
required on AVC cache misses, and performance measurements by James Morris
using a number of benchmarks have shown that the change does not cause any
significant degradation.

Note that a rebuilt policy via an updated policy toolchain
(libsepol/checkpolicy) is required in order to gain the full benefits of
this patch, although some memory savings benefits are immediately applied
even to older policies (in particular, the reduction in avtab node size).
Sources for the updated toolchain are presently available from the
sourceforge CVS tree (http://sourceforge.net/cvs/?group_id=21266), and
tarballs are available from http://www.flux.utah.edu/~sds.

Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: James Morris <jmorris@namei.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 30 insertions, 0 deletions

diff --git a/security/selinux/ss/ebitmap.h b/security/selinux/ss/ebitmap.h
index 471370233fd9..8bf41055a6cb 100644
--- a/security/selinux/ss/ebitmap.h
+++ b/security/selinux/ss/ebitmap.h
@@ -32,11 +32,41 @@ struct ebitmap {
 #define ebitmap_length(e) ((e)->highbit)
 #define ebitmap_startbit(e) ((e)->node ? (e)->node->startbit : 0)
 
+static inline unsigned int ebitmap_start(struct ebitmap *e,
+                                         struct ebitmap_node **n)
+{
+        *n = e->node;
+        return ebitmap_startbit(e);
+}
+
 static inline void ebitmap_init(struct ebitmap *e)
 {
         memset(e, 0, sizeof(*e));
 }
 
+static inline unsigned int ebitmap_next(struct ebitmap_node **n,
+                                        unsigned int bit)
+{
+        if ((bit == ((*n)->startbit + MAPSIZE - 1)) &&
+            (*n)->next) {
+                *n = (*n)->next;
+                return (*n)->startbit;
+        }
+
+        return (bit+1);
+}
+
+static inline int ebitmap_node_get_bit(struct ebitmap_node * n,
+                                       unsigned int bit)
+{
+        if (n->map & (MAPBIT << (bit - n->startbit)))
+                return 1;
+        return 0;
+}
+
+#define ebitmap_for_each_bit(e, n, bit) \
+        for (bit = ebitmap_start(e, &n); bit < ebitmap_length(e); bit = ebitmap_next(&n, bit)) \
+
 int ebitmap_cmp(struct ebitmap *e1, struct ebitmap *e2);
 int ebitmap_cpy(struct ebitmap *dst, struct ebitmap *src);
 int ebitmap_contains(struct ebitmap *e1, struct ebitmap *e2);