X-Git-Url: https://git.saurik.com/apple/xnu.git/blobdiff_plain/d1ecb069dfe24481e4a83f44cb5217a2b06746d7..e2d2fc5c71f7d145cba7267989251af45e3bb5ba:/bsd/dev/random/randomdev.c

diff --git a/bsd/dev/random/randomdev.c b/bsd/dev/random/randomdev.c
index c081bd209..c29e9f877 100644
--- a/bsd/dev/random/randomdev.c
+++ b/bsd/dev/random/randomdev.c
@@ -56,6 +56,7 @@
 #include <dev/random/YarrowCoreLib/include/yarrow.h>
 
 #include <libkern/OSByteOrder.h>
+#include <libkern/OSAtomic.h>
 
 #include <mach/mach_time.h>
 #include <machine/machine_routines.h>
@@ -101,13 +102,14 @@ static struct cdevsw random_cdevsw =
 
 
 /* Used to detect whether we've already been initialized */
-static int gRandomInstalled = 0;
+static UInt8 gRandomInstalled = 0;
 static PrngRef gPrngRef;
 static int gRandomError = 1;
 static lck_grp_t *gYarrowGrp;
 static lck_attr_t *gYarrowAttr;
 static lck_grp_attr_t *gYarrowGrpAttr;
 static lck_mtx_t *gYarrowMutex = 0;
+static UInt8 gYarrowInitializationLock = 0;
 
 #define RESEED_TICKS 50 /* how long a reseed operation can take */
 
@@ -307,6 +309,27 @@ PreliminarySetup(void)
 {
     prng_error_status perr;
 
+	/* Multiple threads can enter this as a result of an earlier
+	 * check of gYarrowMutex.  We make sure that only one of them
+	 * can enter at a time.  If one of them enters and discovers
+	 * that gYarrowMutex is no longer NULL, we know that another
+	 * thread has initialized the Yarrow state and we can exit.
+	 */
+	
+	/* The first thread that enters this function will find
+	 * gYarrowInitializationLock set to 0.  It will atomically
+	 * set the value to 1 and, seeing that it was zero, drop
+	 * out of the loop.  Other threads will see that the value is
+	 * 1 and continue to loop until we are initialized.
+     */
+
+	while (OSTestAndSet(0, &gYarrowInitializationLock)); /* serialize access to this function */
+	
+	if (gYarrowMutex) {
+		/*  we've already been initialized, clear and get out */
+		goto function_exit;
+	}
+
     /* create a Yarrow object */
     perr = prngInitialize(&gPrngRef);
     if (perr != 0) {
@@ -321,6 +344,8 @@ PreliminarySetup(void)
     char buffer [16];
 
     /* get a little non-deterministic data as an initial seed. */
+	/* On OSX, securityd will add much more entropy as soon as it */
+	/* comes up.  On iOS, entropy is added with each system interrupt. */
     microtime(&tt);
 
     /*
@@ -334,7 +359,7 @@ PreliminarySetup(void)
     if (perr != 0) {
         /* an error, complain */
         printf ("Couldn't seed Yarrow.\n");
-        return;
+        goto function_exit;
     }
     
     /* turn the data around */
@@ -350,6 +375,10 @@ PreliminarySetup(void)
     gYarrowMutex   = lck_mtx_alloc_init(gYarrowGrp, gYarrowAttr);
 	
 	fips_initialize ();
+
+function_exit:
+	/* allow other threads to figure out whether or not we have been initialized. */
+	gYarrowInitializationLock = 0;
 }
 
 const Block kKnownAnswer = {0x92, 0xb4, 0x04, 0xe5, 0x56, 0x58, 0x8c, 0xed, 0x6c, 0x1a, 0xcd, 0x4e, 0xbf, 0x05, 0x3f, 0x68, 0x09, 0xf7, 0x3a, 0x93};
@@ -384,14 +413,11 @@ random_init(void)
 {
 	int ret;
 
-	if (gRandomInstalled)
+	if (OSTestAndSet(0, &gRandomInstalled)) {
+		/* do this atomically so that it works correctly with
+		 multiple threads */
 		return;
-
-	/* install us in the file system */
-	gRandomInstalled = 1;
-
-	/* setup yarrow and the mutex */
-	PreliminarySetup();
+	}
 
 	ret = cdevsw_add(RANDOM_MAJOR, &random_cdevsw);
 	if (ret < 0) {
@@ -409,6 +435,9 @@ random_init(void)
 	 */
 	devfs_make_node(makedev (ret, 1), DEVFS_CHAR,
 		UID_ROOT, GID_WHEEL, 0666, "urandom", 0);
+
+	/* setup yarrow and the mutex if needed*/
+	PreliminarySetup();
 }
 
 int