SELinux: improve performance when AVC misses.

* We add ebitmap_for_each_positive_bit() which enables to walk on
  any positive bit on the given ebitmap, to improve its performance
  using common bit-operations defined in linux/bitops.h.
  In the previous version, this logic was implemented using a combination
  of ebitmap_for_each_bit() and ebitmap_node_get_bit(), but is was worse
  in performance aspect.
  This logic is most frequestly used to compute a new AVC entry,
  so this patch can improve SELinux performance when AVC misses are happen.
* struct ebitmap_node is redefined as an array of "unsigned long", to get
  suitable for using find_next_bit() which is fasted than iteration of
  shift and logical operation, and to maximize memory usage allocated
  from general purpose slab.
* Any ebitmap_for_each_bit() are repleced by the new implementation
  in ss/service.c and ss/mls.c. Some of related implementation are
  changed, however, there is no incompatibility with the previous
  version.
* The width of any new line are less or equal than 80-chars.

The following benchmark shows the effect of this patch, when we
access many files which have different security context one after
another. The number is more than /selinux/avc/cache_threshold, so
any access always causes AVC misses.

      selinux-2.6      selinux-2.6-ebitmap
AVG:   22.763 [s]          8.750 [s]
STD:    0.265              0.019
------------------------------------------
1st:   22.558 [s]          8.786 [s]
2nd:   22.458 [s]          8.750 [s]
3rd:   22.478 [s]          8.754 [s]
4th:   22.724 [s]          8.745 [s]
5th:   22.918 [s]          8.748 [s]
6th:   22.905 [s]          8.764 [s]
7th:   23.238 [s]          8.726 [s]
8th:   22.822 [s]          8.729 [s]

Signed-off-by: KaiGai Kohei <kaigai@ak.jp.nec.com>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: James Morris <jmorris@namei.org>

1 files changed, 75 insertions, 81 deletions

diff --git a/security/selinux/ss/mls.c b/security/selinux/ss/mls.c
index 4a8bab2f3c71..9a11deaaa9e7 100644
--- a/security/selinux/ss/mls.c
+++ b/security/selinux/ss/mls.c
@@ -34,7 +34,9 @@
  */
 int mls_compute_context_len(struct context * context)
 {
-	int i, l, len, range;
+	int i, l, len, head, prev;
+	char *nm;
+	struct ebitmap *e;
 	struct ebitmap_node *node;
 
 	if (!selinux_mls_enabled)
@@ -42,31 +44,33 @@ int mls_compute_context_len(struct context * context)
 
 	len = 1; /* for the beginning ":" */
 	for (l = 0; l < 2; l++) {
-		range = 0;
-		len += strlen(policydb.p_sens_val_to_name[context->range.level[l].sens - 1]);
-
-		ebitmap_for_each_bit(&context->range.level[l].cat, node, i) {
-			if (ebitmap_node_get_bit(node, i)) {
-				if (range) {
-					range++;
-					continue;
-				}
+		int index_sens = context->range.level[l].sens;
+		len += strlen(policydb.p_sens_val_to_name[index_sens - 1]);
 
-				len += strlen(policydb.p_cat_val_to_name[i]) + 1;
-				range++;
-			} else {
-				if (range > 1)
-					len += strlen(policydb.p_cat_val_to_name[i - 1]) + 1;
-				range = 0;
+		/* categories */
+		head = -2;
+		prev = -2;
+		e = &context->range.level[l].cat;
+		ebitmap_for_each_positive_bit(e, node, i) {
+			if (i - prev > 1) {
+				/* one or more negative bits are skipped */
+				if (head != prev) {
+					nm = policydb.p_cat_val_to_name[prev];
+					len += strlen(nm) + 1;
+				}
+				nm = policydb.p_cat_val_to_name[i];
+				len += strlen(nm) + 1;
+				head = i;
 			}
+			prev = i;
+		}
+		if (prev != head) {
+			nm = policydb.p_cat_val_to_name[prev];
+			len += strlen(nm) + 1;
 		}
-		/* Handle case where last category is the end of range */
-		if (range > 1)
-			len += strlen(policydb.p_cat_val_to_name[i - 1]) + 1;
-
 		if (l == 0) {
 			if (mls_level_eq(&context->range.level[0],
-			                 &context->range.level[1]))
+					 &context->range.level[1]))
 				break;
 			else
 				len++;
@@ -84,8 +88,9 @@ int mls_compute_context_len(struct context * context)
 void mls_sid_to_context(struct context *context,
                         char **scontext)
 {
-	char *scontextp;
-	int i, l, range, wrote_sep;
+	char *scontextp, *nm;
+	int i, l, head, prev;
+	struct ebitmap *e;
 	struct ebitmap_node *node;
 
 	if (!selinux_mls_enabled)
@@ -97,61 +102,54 @@ void mls_sid_to_context(struct context *context,
 	scontextp++;
 
 	for (l = 0; l < 2; l++) {
-		range = 0;
-		wrote_sep = 0;
 		strcpy(scontextp,
 		       policydb.p_sens_val_to_name[context->range.level[l].sens - 1]);
-		scontextp += strlen(policydb.p_sens_val_to_name[context->range.level[l].sens - 1]);
+		scontextp += strlen(scontextp);
 
 		/* categories */
-		ebitmap_for_each_bit(&context->range.level[l].cat, node, i) {
-			if (ebitmap_node_get_bit(node, i)) {
-				if (range) {
-					range++;
-					continue;
-				}
-
-				if (!wrote_sep) {
-					*scontextp++ = ':';
-					wrote_sep = 1;
-				} else
-					*scontextp++ = ',';
-				strcpy(scontextp, policydb.p_cat_val_to_name[i]);
-				scontextp += strlen(policydb.p_cat_val_to_name[i]);
-				range++;
-			} else {
-				if (range > 1) {
-					if (range > 2)
+		head = -2;
+		prev = -2;
+		e = &context->range.level[l].cat;
+		ebitmap_for_each_positive_bit(e, node, i) {
+			if (i - prev > 1) {
+				/* one or more negative bits are skipped */
+				if (prev != head) {
+					if (prev - head > 1)
 						*scontextp++ = '.';
 					else
 						*scontextp++ = ',';
-
-					strcpy(scontextp, policydb.p_cat_val_to_name[i - 1]);
-					scontextp += strlen(policydb.p_cat_val_to_name[i - 1]);
+					nm = policydb.p_cat_val_to_name[prev];
+					strcpy(scontextp, nm);
+					scontextp += strlen(nm);
 				}
-				range = 0;
+				if (prev < 0)
+					*scontextp++ = ':';
+				else
+					*scontextp++ = ',';
+				nm = policydb.p_cat_val_to_name[i];
+				strcpy(scontextp, nm);
+				scontextp += strlen(nm);
+				head = i;
 			}
+			prev = i;
 		}
 
-		/* Handle case where last category is the end of range */
-		if (range > 1) {
-			if (range > 2)
+		if (prev != head) {
+			if (prev - head > 1)
 				*scontextp++ = '.';
 			else
 				*scontextp++ = ',';
-
-			strcpy(scontextp, policydb.p_cat_val_to_name[i - 1]);
-			scontextp += strlen(policydb.p_cat_val_to_name[i - 1]);
+			nm = policydb.p_cat_val_to_name[prev];
+			strcpy(scontextp, nm);
+			scontextp += strlen(nm);
 		}
 
 		if (l == 0) {
 			if (mls_level_eq(&context->range.level[0],
 			                 &context->range.level[1]))
 				break;
-			else {
-				*scontextp = '-';
-				scontextp++;
-			}
+			else
+				*scontextp++ = '-';
 		}
 	}
 
@@ -190,17 +188,15 @@ int mls_context_isvalid(struct policydb *p, struct context *c)
 		if (!levdatum)
 			return 0;
 
-		ebitmap_for_each_bit(&c->range.level[l].cat, node, i) {
-			if (ebitmap_node_get_bit(node, i)) {
-				if (i > p->p_cats.nprim)
-					return 0;
-				if (!ebitmap_get_bit(&levdatum->level->cat, i))
-					/*
-					 * Category may not be associated with
-					 * sensitivity in low level.
-					 */
-					return 0;
-			}
+		ebitmap_for_each_positive_bit(&c->range.level[l].cat, node, i) {
+			if (i > p->p_cats.nprim)
+				return 0;
+			if (!ebitmap_get_bit(&levdatum->level->cat, i))
+				/*
+				 * Category may not be associated with
+				 * sensitivity in low level.
+				 */
+				return 0;
 		}
 	}
 
@@ -485,18 +481,16 @@ int mls_convert_context(struct policydb *oldp,
 		c->range.level[l].sens = levdatum->level->sens;
 
 		ebitmap_init(&bitmap);
-		ebitmap_for_each_bit(&c->range.level[l].cat, node, i) {
-			if (ebitmap_node_get_bit(node, i)) {
-				int rc;
-
-				catdatum = hashtab_search(newp->p_cats.table,
-				         	oldp->p_cat_val_to_name[i]);
-				if (!catdatum)
-					return -EINVAL;
-				rc = ebitmap_set_bit(&bitmap, catdatum->value - 1, 1);
-				if (rc)
-					return rc;
-			}
+		ebitmap_for_each_positive_bit(&c->range.level[l].cat, node, i) {
+			int rc;
+
+			catdatum = hashtab_search(newp->p_cats.table,
+						  oldp->p_cat_val_to_name[i]);
+			if (!catdatum)
+				return -EINVAL;
+			rc = ebitmap_set_bit(&bitmap, catdatum->value - 1, 1);
+			if (rc)
+				return rc;
 		}
 		ebitmap_destroy(&c->range.level[l].cat);
 		c->range.level[l].cat = bitmap;