Merge tag 'random_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/random

Pull randomness updates from Ted Ts'o:

 - initialize the random driver earler

 - fix CRNG initialization when we trust the CPU's RNG on NUMA systems

 - other miscellaneous cleanups and fixes.

* tag 'random_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/random:
  random: add a spinlock_t to struct batched_entropy
  random: document get_random_int() family
  random: fix CRNG initialization when random.trust_cpu=1
  random: move rand_initialize() earlier
  random: only read from /dev/random after its pool has received 128 bits
  drivers/char/random.c: make primary_crng static
  drivers/char/random.c: remove unused stuct poolinfo::poolbits
  drivers/char/random.c: constify poolinfo_table

Author: torvalds

drivers/char/random.c

@@ -101,15 +101,13 @@
  * Exported interfaces ---- output
  * ===============================
  *
- * There are three exported interfaces; the first is one designed to
- * be used from within the kernel:
+ * There are four exported interfaces; two for use within the kernel,
+ * and two or use from userspace.
  *
- * 	void get_random_bytes(void *buf, int nbytes);
- *
- * This interface will return the requested number of random bytes,
- * and place it in the requested buffer.
+ * Exported interfaces ---- userspace output
+ * -----------------------------------------
  *
- * The two other interfaces are two character devices /dev/random and
+ * The userspace interfaces are two character devices /dev/random and
  * /dev/urandom.  /dev/random is suitable for use when very high
  * quality randomness is desired (for example, for key generation or
  * one-time pads), as it will only return a maximum of the number of
@@ -122,6 +120,77 @@
  * this will result in random numbers that are merely cryptographically
  * strong.  For many applications, however, this is acceptable.
  *
+ * Exported interfaces ---- kernel output
+ * --------------------------------------
+ *
+ * The primary kernel interface is
+ *
+ * 	void get_random_bytes(void *buf, int nbytes);
+ *
+ * This interface will return the requested number of random bytes,
+ * and place it in the requested buffer.  This is equivalent to a
+ * read from /dev/urandom.
+ *
+ * For less critical applications, there are the functions:
+ *
+ * 	u32 get_random_u32()
+ * 	u64 get_random_u64()
+ * 	unsigned int get_random_int()
+ * 	unsigned long get_random_long()
+ *
+ * These are produced by a cryptographic RNG seeded from get_random_bytes,
+ * and so do not deplete the entropy pool as much.  These are recommended
+ * for most in-kernel operations *if the result is going to be stored in
+ * the kernel*.
+ *
+ * Specifically, the get_random_int() family do not attempt to do
+ * "anti-backtracking".  If you capture the state of the kernel (e.g.
+ * by snapshotting the VM), you can figure out previous get_random_int()
+ * return values.  But if the value is stored in the kernel anyway,
+ * this is not a problem.
+ *
+ * It *is* safe to expose get_random_int() output to attackers (e.g. as
+ * network cookies); given outputs 1..n, it's not feasible to predict
+ * outputs 0 or n+1.  The only concern is an attacker who breaks into
+ * the kernel later; the get_random_int() engine is not reseeded as
+ * often as the get_random_bytes() one.
+ *
+ * get_random_bytes() is needed for keys that need to stay secret after
+ * they are erased from the kernel.  For example, any key that will
+ * be wrapped and stored encrypted.  And session encryption keys: we'd
+ * like to know that after the session is closed and the keys erased,
+ * the plaintext is unrecoverable to someone who recorded the ciphertext.
+ *
+ * But for network ports/cookies, stack canaries, PRNG seeds, address
+ * space layout randomization, session *authentication* keys, or other
+ * applications where the sensitive data is stored in the kernel in
+ * plaintext for as long as it's sensitive, the get_random_int() family
+ * is just fine.
+ *
+ * Consider ASLR.  We want to keep the address space secret from an
+ * outside attacker while the process is running, but once the address
+ * space is torn down, it's of no use to an attacker any more.  And it's
+ * stored in kernel data structures as long as it's alive, so worrying
+ * about an attacker's ability to extrapolate it from the get_random_int()
+ * CRNG is silly.
+ *
+ * Even some cryptographic keys are safe to generate with get_random_int().
+ * In particular, keys for SipHash are generally fine.  Here, knowledge
+ * of the key authorizes you to do something to a kernel object (inject
+ * packets to a network connection, or flood a hash table), and the
+ * key is stored with the object being protected.  Once it goes away,
+ * we no longer care if anyone knows the key.
+ *
+ * prandom_u32()
+ * -------------
+ *
+ * For even weaker applications, see the pseudorandom generator
+ * prandom_u32(), prandom_max(), and prandom_bytes().  If the random
+ * numbers aren't security-critical at all, these are *far* cheaper.
+ * Useful for self-tests, random error simulation, randomized backoffs,
+ * and any other application where you trust that nobody is trying to
+ * maliciously mess with you by guessing the "random" numbers.
+ *
  * Exported interfaces ---- input
  * ==============================
  *
@@ -295,7 +364,7 @@
  * To allow fractional bits to be tracked, the entropy_count field is
  * denominated in units of 1/8th bits.
  *
- * 2*(ENTROPY_SHIFT + log2(poolbits)) must <= 31, or the multiply in
+ * 2*(ENTROPY_SHIFT + poolbitshift) must <= 31, or the multiply in
  * credit_entropy_bits() needs to be 64 bits wide.
  */
 #define ENTROPY_SHIFT 3
@@ -359,9 +428,9 @@ static int random_write_wakeup_bits = 28 * OUTPUT_POOL_WORDS;
  * polynomial which improves the resulting TGFSR polynomial to be
  * irreducible, which we have made here.
  */
-static struct poolinfo {
-	int poolbitshift, poolwords, poolbytes, poolbits, poolfracbits;
-#define S(x) ilog2(x)+5, (x), (x)*4, (x)*32, (x) << (ENTROPY_SHIFT+5)
+static const struct poolinfo {
+	int poolbitshift, poolwords, poolbytes, poolfracbits;
+#define S(x) ilog2(x)+5, (x), (x)*4, (x) << (ENTROPY_SHIFT+5)
 	int tap1, tap2, tap3, tap4, tap5;
 } poolinfo_table[] = {
 	/* was: x^128 + x^103 + x^76 + x^51 +x^25 + x + 1 */
@@ -415,7 +484,7 @@ struct crng_state {
 	spinlock_t	lock;
 };
 
-struct crng_state primary_crng = {
+static struct crng_state primary_crng = {
 	.lock = __SPIN_LOCK_UNLOCKED(primary_crng.lock),
 };
 
@@ -470,7 +539,6 @@ struct entropy_store {
 	unsigned short add_ptr;
 	unsigned short input_rotate;
 	int entropy_count;
-	int entropy_total;
 	unsigned int initialized:1;
 	unsigned int last_data_init:1;
 	__u8 last_data[EXTRACT_SIZE];
@@ -643,7 +711,7 @@ static void process_random_ready_list(void)
  */
 static void credit_entropy_bits(struct entropy_store *r, int nbits)
 {
-	int entropy_count, orig;
+	int entropy_count, orig, has_initialized = 0;
 	const int pool_size = r->poolinfo->poolfracbits;
 	int nfrac = nbits << ENTROPY_SHIFT;
 
@@ -698,23 +766,25 @@ static void credit_entropy_bits(struct entropy_store *r, int nbits)
 		entropy_count = 0;
 	} else if (entropy_count > pool_size)
 		entropy_count = pool_size;
+	if ((r == &blocking_pool) && !r->initialized &&
+	    (entropy_count >> ENTROPY_SHIFT) > 128)
+		has_initialized = 1;
 	if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
 		goto retry;
 
-	r->entropy_total += nbits;
-	if (!r->initialized && r->entropy_total > 128) {
+	if (has_initialized)
 		r->initialized = 1;
-		r->entropy_total = 0;
-	}
 
 	trace_credit_entropy_bits(r->name, nbits,
-				  entropy_count >> ENTROPY_SHIFT,
-				  r->entropy_total, _RET_IP_);
+				  entropy_count >> ENTROPY_SHIFT, _RET_IP_);
 
 	if (r == &input_pool) {
 		int entropy_bits = entropy_count >> ENTROPY_SHIFT;
+		struct entropy_store *other = &blocking_pool;
 
-		if (crng_init < 2 && entropy_bits >= 128) {
+		if (crng_init < 2) {
+			if (entropy_bits < 128)
+				return;
 			crng_reseed(&primary_crng, r);
 			entropy_bits = r->entropy_count >> ENTROPY_SHIFT;
 		}
@@ -725,20 +795,14 @@ static void credit_entropy_bits(struct entropy_store *r, int nbits)
 			wake_up_interruptible(&random_read_wait);
 			kill_fasync(&fasync, SIGIO, POLL_IN);
 		}
-		/* If the input pool is getting full, send some
-		 * entropy to the blocking pool until it is 75% full.
+		/* If the input pool is getting full, and the blocking
+		 * pool has room, send some entropy to the blocking
+		 * pool.
 		 */
-		if (entropy_bits > random_write_wakeup_bits &&
-		    r->initialized &&
-		    r->entropy_total >= 2*random_read_wakeup_bits) {
-			struct entropy_store *other = &blocking_pool;
-
-			if (other->entropy_count <=
-			    3 * other->poolinfo->poolfracbits / 4) {
-				schedule_work(&other->push_work);
-				r->entropy_total = 0;
-			}
-		}
+		if (!work_pending(&other->push_work) &&
+		    (ENTROPY_BITS(r) > 6 * r->poolinfo->poolbytes) &&
+		    (ENTROPY_BITS(other) <= 6 * other->poolinfo->poolbytes))
+			schedule_work(&other->push_work);
 	}
 }
 
@@ -777,6 +841,7 @@ static struct crng_state **crng_node_pool __read_mostly;
 #endif
 
 static void invalidate_batched_entropy(void);
+static void numa_crng_init(void);
 
 static bool trust_cpu __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU);
 static int __init parse_trust_cpu(char *arg)
@@ -805,7 +870,9 @@ static void crng_initialize(struct crng_state *crng)
 		}
 		crng->state[i] ^= rv;
 	}
-	if (trust_cpu && arch_init) {
+	if (trust_cpu && arch_init && crng == &primary_crng) {
+		invalidate_batched_entropy();
+		numa_crng_init();
 		crng_init = 2;
 		pr_notice("random: crng done (trusting CPU's manufacturer)\n");
 	}
@@ -1553,6 +1620,11 @@ static ssize_t extract_entropy_user(struct entropy_store *r, void __user *buf,
 	int large_request = (nbytes > 256);
 
 	trace_extract_entropy_user(r->name, nbytes, ENTROPY_BITS(r), _RET_IP_);
+	if (!r->initialized && r->pull) {
+		xfer_secondary_pool(r, ENTROPY_BITS(r->pull)/8);
+		if (!r->initialized)
+			return 0;
+	}
 	xfer_secondary_pool(r, nbytes);
 	nbytes = account(r, nbytes, 0, 0);
 
@@ -1783,7 +1855,7 @@ EXPORT_SYMBOL(get_random_bytes_arch);
  * data into the pool to prepare it for use. The pool is not cleared
  * as that can only decrease the entropy in the pool.
  */
-static void init_std_data(struct entropy_store *r)
+static void __init init_std_data(struct entropy_store *r)
 {
 	int i;
 	ktime_t now = ktime_get_real();
@@ -1810,7 +1882,7 @@ static void init_std_data(struct entropy_store *r)
  * take care not to overwrite the precious per platform data
  * we were given.
  */
-static int rand_initialize(void)
+int __init rand_initialize(void)
 {
 	init_std_data(&input_pool);
 	init_std_data(&blocking_pool);
@@ -1822,7 +1894,6 @@ static int rand_initialize(void)
 	}
 	return 0;
 }
-early_initcall(rand_initialize);
 
 #ifdef CONFIG_BLOCK
 void rand_initialize_disk(struct gendisk *disk)
@@ -2211,8 +2282,8 @@ struct batched_entropy {
 		u32 entropy_u32[CHACHA_BLOCK_SIZE / sizeof(u32)];
 	};
 	unsigned int position;
+	spinlock_t batch_lock;
 };
-static rwlock_t batched_entropy_reset_lock = __RW_LOCK_UNLOCKED(batched_entropy_reset_lock);
 
 /*
  * Get a random word for internal kernel use only. The quality of the random
@@ -2222,12 +2293,14 @@ static rwlock_t batched_entropy_reset_lock = __RW_LOCK_UNLOCKED(batched_entropy_
  * wait_for_random_bytes() should be called and return 0 at least once
  * at any point prior.
  */
-static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u64);
+static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u64) = {
+	.batch_lock	= __SPIN_LOCK_UNLOCKED(batched_entropy_u64.lock),
+};
+
 u64 get_random_u64(void)
 {
 	u64 ret;
-	bool use_lock;
-	unsigned long flags = 0;
+	unsigned long flags;
 	struct batched_entropy *batch;
 	static void *previous;
 
@@ -2242,28 +2315,25 @@ u64 get_random_u64(void)
 
 	warn_unseeded_randomness(&previous);
 
-	use_lock = READ_ONCE(crng_init) < 2;
-	batch = &get_cpu_var(batched_entropy_u64);
-	if (use_lock)
-		read_lock_irqsave(&batched_entropy_reset_lock, flags);
+	batch = raw_cpu_ptr(&batched_entropy_u64);
+	spin_lock_irqsave(&batch->batch_lock, flags);
 	if (batch->position % ARRAY_SIZE(batch->entropy_u64) == 0) {
 		extract_crng((u8 *)batch->entropy_u64);
 		batch->position = 0;
 	}
 	ret = batch->entropy_u64[batch->position++];
-	if (use_lock)
-		read_unlock_irqrestore(&batched_entropy_reset_lock, flags);
-	put_cpu_var(batched_entropy_u64);
+	spin_unlock_irqrestore(&batch->batch_lock, flags);
 	return ret;
 }
 EXPORT_SYMBOL(get_random_u64);
 
-static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u32);
+static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u32) = {
+	.batch_lock	= __SPIN_LOCK_UNLOCKED(batched_entropy_u32.lock),
+};
 u32 get_random_u32(void)
 {
 	u32 ret;
-	bool use_lock;
-	unsigned long flags = 0;
+	unsigned long flags;
 	struct batched_entropy *batch;
 	static void *previous;
 
@@ -2272,18 +2342,14 @@ u32 get_random_u32(void)
 
 	warn_unseeded_randomness(&previous);
 
-	use_lock = READ_ONCE(crng_init) < 2;
-	batch = &get_cpu_var(batched_entropy_u32);
-	if (use_lock)
-		read_lock_irqsave(&batched_entropy_reset_lock, flags);
+	batch = raw_cpu_ptr(&batched_entropy_u32);
+	spin_lock_irqsave(&batch->batch_lock, flags);
 	if (batch->position % ARRAY_SIZE(batch->entropy_u32) == 0) {
 		extract_crng((u8 *)batch->entropy_u32);
 		batch->position = 0;
 	}
 	ret = batch->entropy_u32[batch->position++];
-	if (use_lock)
-		read_unlock_irqrestore(&batched_entropy_reset_lock, flags);
-	put_cpu_var(batched_entropy_u32);
+	spin_unlock_irqrestore(&batch->batch_lock, flags);
 	return ret;
 }
 EXPORT_SYMBOL(get_random_u32);
@@ -2297,12 +2363,19 @@ static void invalidate_batched_entropy(void)
 	int cpu;
 	unsigned long flags;
 
-	write_lock_irqsave(&batched_entropy_reset_lock, flags);
 	for_each_possible_cpu (cpu) {
-		per_cpu_ptr(&batched_entropy_u32, cpu)->position = 0;
-		per_cpu_ptr(&batched_entropy_u64, cpu)->position = 0;
+		struct batched_entropy *batched_entropy;
+
+		batched_entropy = per_cpu_ptr(&batched_entropy_u32, cpu);
+		spin_lock_irqsave(&batched_entropy->batch_lock, flags);
+		batched_entropy->position = 0;
+		spin_unlock(&batched_entropy->batch_lock);
+
+		batched_entropy = per_cpu_ptr(&batched_entropy_u64, cpu);
+		spin_lock(&batched_entropy->batch_lock);
+		batched_entropy->position = 0;
+		spin_unlock_irqrestore(&batched_entropy->batch_lock, flags);
 	}
-	write_unlock_irqrestore(&batched_entropy_reset_lock, flags);
 }
 
 /**

include/linux/random.h

@@ -36,6 +36,7 @@ extern void add_interrupt_randomness(int irq, int irq_flags) __latent_entropy;
 
 extern void get_random_bytes(void *buf, int nbytes);
 extern int wait_for_random_bytes(void);
+extern int __init rand_initialize(void);
 extern bool rng_is_initialized(void);
 extern int add_random_ready_callback(struct random_ready_callback *rdy);
 extern void del_random_ready_callback(struct random_ready_callback *rdy);