[PATCH 3/9] SELinux: Expose AVC sizing tunables via Kconfig

[siarhei.liakh@concurrent-rt.com]

From: Siarhei Liakh <siarhei.liakh@concurrent-rt.com>

This change exposes previously hardcoded AVC sizing tunables via Kconfig,
which provides a more convenient tuning mechanism for downstream distributions.
Default sizing is not affected.

Signed-off-by: Siarhei Liakh <siarhei.liakh@concurrent-rt.com>
---
Please CC me directly in all replies.

 security/selinux/Kconfig | 32 ++++++++++++++++++++++++++++++++
 security/selinux/avc.c   |  6 +++---
 2 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/security/selinux/Kconfig b/security/selinux/Kconfig
index 4b5c9fa510a1..3a736a1c6806 100644
--- a/security/selinux/Kconfig
+++ b/security/selinux/Kconfig
@@ -79,6 +79,38 @@ config SECURITY_SELINUX_AVC_STATS
 	  /sys/fs/selinux/avc/cache_stats, which may be monitored via
 	  tools such as avcstat.
 
+config SECURITY_SELINUX_AVC_DEF_THRESHOLD
+	int "Default value for AVC reclamation threshold"
+	depends on SECURITY_SELINUX
+	range 64 1048576
+	default "512"
+	help
+	  Reclamation threshold effectively sets a limit on AVC size.
+	  Increasing this number could improve performance of busy
+	  systems with lots of complex policies. Threshold value can
+	  also be changed at run-time via selinuxfs.
+
+config SECURITY_SELINUX_AVC_HASH_BITS
+	int "Number of slots (buckets) for AVC hash table, expressed as number of bits (i.e. 2^n)"
+	depends on SECURITY_SELINUX
+	range 1 32
+	default "9"
+	help
+	  This is a power of 2 representing the number of slots (buckets)
+	  used for AVC hash table. Smaller value reduces memory footprint
+	  at price of hash table lookup efficiency.
+
+config SECURITY_SELINUX_AVC_RECLAIM_COUNT
+	int "Number of AVC entries to reclaim in a single cycle"
+	depends on SECURITY_SELINUX
+	range 1 SECURITY_SELINUX_AVC_DEF_THRESHOLD
+	default "16"
+	help
+	  A single reclamation cycle will evict this many AVC entries
+	  from the cache. Small values may require multiple reclamation
+	  cycles to bring AVC size under the threshold. Large values may
+	  cause excessive latency of reclamation events.
+
 config SECURITY_SELINUX_CHECKREQPROT_VALUE
 	int "NSA SELinux checkreqprot default value"
 	depends on SECURITY_SELINUX
diff --git a/security/selinux/avc.c b/security/selinux/avc.c
index b5893621290b..80af3d1f31fd 100644
--- a/security/selinux/avc.c
+++ b/security/selinux/avc.c
@@ -31,9 +31,9 @@
 #include "avc_ss.h"
 #include "classmap.h"
 
-#define AVC_CACHE_SLOTS			512
-#define AVC_DEF_CACHE_THRESHOLD		512
-#define AVC_CACHE_RECLAIM		16
+#define AVC_CACHE_SLOTS			(1 << CONFIG_SECURITY_SELINUX_AVC_HASH_BITS)
+#define AVC_DEF_CACHE_THRESHOLD		CONFIG_SECURITY_SELINUX_AVC_DEF_THRESHOLD
+#define AVC_CACHE_RECLAIM		CONFIG_SECURITY_SELINUX_AVC_RECLAIM_COUNT
 
 #ifdef CONFIG_SECURITY_SELINUX_AVC_STATS
 #define avc_cache_stats_incr(field)	this_cpu_inc(avc_cache_stats.field)
-- 
2.17.1