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Subject[PATCH 4.19 100/234] random: group entropy extraction functions
Date
From: "Jason A. Donenfeld" <Jason@zx2c4.com>

commit a5ed7cb1a7732ef11959332d507889fbc39ebbb4 upstream.

This pulls all of the entropy extraction-focused functions into the
third labeled section.

No functional changes.

Cc: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/char/random.c | 216 +++++++++++++++++++++++++-------------------------
1 file changed, 109 insertions(+), 107 deletions(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -890,23 +890,36 @@ size_t __must_check get_random_bytes_arc
}
EXPORT_SYMBOL(get_random_bytes_arch);

+
+/**********************************************************************
+ *
+ * Entropy accumulation and extraction routines.
+ *
+ * Callers may add entropy via:
+ *
+ * static void mix_pool_bytes(const void *in, size_t nbytes)
+ *
+ * After which, if added entropy should be credited:
+ *
+ * static void credit_entropy_bits(size_t nbits)
+ *
+ * Finally, extract entropy via these two, with the latter one
+ * setting the entropy count to zero and extracting only if there
+ * is POOL_MIN_BITS entropy credited prior:
+ *
+ * static void extract_entropy(void *buf, size_t nbytes)
+ * static bool drain_entropy(void *buf, size_t nbytes)
+ *
+ **********************************************************************/
+
enum {
POOL_BITS = BLAKE2S_HASH_SIZE * 8,
POOL_MIN_BITS = POOL_BITS /* No point in settling for less. */
};

-/*
- * Static global variables
- */
+/* For notifying userspace should write into /dev/random. */
static DECLARE_WAIT_QUEUE_HEAD(random_write_wait);

-/**********************************************************************
- *
- * OS independent entropy store. Here are the functions which handle
- * storing entropy in an entropy pool.
- *
- **********************************************************************/
-
static struct {
struct blake2s_state hash;
spinlock_t lock;
@@ -919,28 +932,106 @@ static struct {
.lock = __SPIN_LOCK_UNLOCKED(input_pool.lock),
};

-static void extract_entropy(void *buf, size_t nbytes);
-static bool drain_entropy(void *buf, size_t nbytes);
-
-static void crng_reseed(void);
+static void _mix_pool_bytes(const void *in, size_t nbytes)
+{
+ blake2s_update(&input_pool.hash, in, nbytes);
+}

/*
* This function adds bytes into the entropy "pool". It does not
* update the entropy estimate. The caller should call
* credit_entropy_bits if this is appropriate.
*/
-static void _mix_pool_bytes(const void *in, size_t nbytes)
+static void mix_pool_bytes(const void *in, size_t nbytes)
{
- blake2s_update(&input_pool.hash, in, nbytes);
+ unsigned long flags;
+
+ spin_lock_irqsave(&input_pool.lock, flags);
+ _mix_pool_bytes(in, nbytes);
+ spin_unlock_irqrestore(&input_pool.lock, flags);
}

-static void mix_pool_bytes(const void *in, size_t nbytes)
+static void credit_entropy_bits(size_t nbits)
+{
+ unsigned int entropy_count, orig, add;
+
+ if (!nbits)
+ return;
+
+ add = min_t(size_t, nbits, POOL_BITS);
+
+ do {
+ orig = READ_ONCE(input_pool.entropy_count);
+ entropy_count = min_t(unsigned int, POOL_BITS, orig + add);
+ } while (cmpxchg(&input_pool.entropy_count, orig, entropy_count) != orig);
+
+ if (crng_init < 2 && entropy_count >= POOL_MIN_BITS)
+ crng_reseed();
+}
+
+/*
+ * This is an HKDF-like construction for using the hashed collected entropy
+ * as a PRF key, that's then expanded block-by-block.
+ */
+static void extract_entropy(void *buf, size_t nbytes)
{
unsigned long flags;
+ u8 seed[BLAKE2S_HASH_SIZE], next_key[BLAKE2S_HASH_SIZE];
+ struct {
+ unsigned long rdseed[32 / sizeof(long)];
+ size_t counter;
+ } block;
+ size_t i;
+
+ for (i = 0; i < ARRAY_SIZE(block.rdseed); ++i) {
+ if (!arch_get_random_seed_long(&block.rdseed[i]) &&
+ !arch_get_random_long(&block.rdseed[i]))
+ block.rdseed[i] = random_get_entropy();
+ }

spin_lock_irqsave(&input_pool.lock, flags);
- _mix_pool_bytes(in, nbytes);
+
+ /* seed = HASHPRF(last_key, entropy_input) */
+ blake2s_final(&input_pool.hash, seed);
+
+ /* next_key = HASHPRF(seed, RDSEED || 0) */
+ block.counter = 0;
+ blake2s(next_key, (u8 *)&block, seed, sizeof(next_key), sizeof(block), sizeof(seed));
+ blake2s_init_key(&input_pool.hash, BLAKE2S_HASH_SIZE, next_key, sizeof(next_key));
+
spin_unlock_irqrestore(&input_pool.lock, flags);
+ memzero_explicit(next_key, sizeof(next_key));
+
+ while (nbytes) {
+ i = min_t(size_t, nbytes, BLAKE2S_HASH_SIZE);
+ /* output = HASHPRF(seed, RDSEED || ++counter) */
+ ++block.counter;
+ blake2s(buf, (u8 *)&block, seed, i, sizeof(block), sizeof(seed));
+ nbytes -= i;
+ buf += i;
+ }
+
+ memzero_explicit(seed, sizeof(seed));
+ memzero_explicit(&block, sizeof(block));
+}
+
+/*
+ * First we make sure we have POOL_MIN_BITS of entropy in the pool, and then we
+ * set the entropy count to zero (but don't actually touch any data). Only then
+ * can we extract a new key with extract_entropy().
+ */
+static bool drain_entropy(void *buf, size_t nbytes)
+{
+ unsigned int entropy_count;
+ do {
+ entropy_count = READ_ONCE(input_pool.entropy_count);
+ if (entropy_count < POOL_MIN_BITS)
+ return false;
+ } while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count);
+ extract_entropy(buf, nbytes);
+ wake_up_interruptible(&random_write_wait);
+ kill_fasync(&fasync, SIGIO, POLL_OUT);
+ return true;
}

struct fast_pool {
@@ -983,24 +1074,6 @@ static void fast_mix(u32 pool[4])
pool[2] = c; pool[3] = d;
}

-static void credit_entropy_bits(size_t nbits)
-{
- unsigned int entropy_count, orig, add;
-
- if (!nbits)
- return;
-
- add = min_t(size_t, nbits, POOL_BITS);
-
- do {
- orig = READ_ONCE(input_pool.entropy_count);
- entropy_count = min_t(unsigned int, POOL_BITS, orig + add);
- } while (cmpxchg(&input_pool.entropy_count, orig, entropy_count) != orig);
-
- if (crng_init < 2 && entropy_count >= POOL_MIN_BITS)
- crng_reseed();
-}
-
/*********************************************************************
*
* Entropy input management
@@ -1197,77 +1270,6 @@ void add_disk_randomness(struct gendisk
EXPORT_SYMBOL_GPL(add_disk_randomness);
#endif

-/*********************************************************************
- *
- * Entropy extraction routines
- *
- *********************************************************************/
-
-/*
- * This is an HKDF-like construction for using the hashed collected entropy
- * as a PRF key, that's then expanded block-by-block.
- */
-static void extract_entropy(void *buf, size_t nbytes)
-{
- unsigned long flags;
- u8 seed[BLAKE2S_HASH_SIZE], next_key[BLAKE2S_HASH_SIZE];
- struct {
- unsigned long rdseed[32 / sizeof(long)];
- size_t counter;
- } block;
- size_t i;
-
- for (i = 0; i < ARRAY_SIZE(block.rdseed); ++i) {
- if (!arch_get_random_seed_long(&block.rdseed[i]) &&
- !arch_get_random_long(&block.rdseed[i]))
- block.rdseed[i] = random_get_entropy();
- }
-
- spin_lock_irqsave(&input_pool.lock, flags);
-
- /* seed = HASHPRF(last_key, entropy_input) */
- blake2s_final(&input_pool.hash, seed);
-
- /* next_key = HASHPRF(seed, RDSEED || 0) */
- block.counter = 0;
- blake2s(next_key, (u8 *)&block, seed, sizeof(next_key), sizeof(block), sizeof(seed));
- blake2s_init_key(&input_pool.hash, BLAKE2S_HASH_SIZE, next_key, sizeof(next_key));
-
- spin_unlock_irqrestore(&input_pool.lock, flags);
- memzero_explicit(next_key, sizeof(next_key));
-
- while (nbytes) {
- i = min_t(size_t, nbytes, BLAKE2S_HASH_SIZE);
- /* output = HASHPRF(seed, RDSEED || ++counter) */
- ++block.counter;
- blake2s(buf, (u8 *)&block, seed, i, sizeof(block), sizeof(seed));
- nbytes -= i;
- buf += i;
- }
-
- memzero_explicit(seed, sizeof(seed));
- memzero_explicit(&block, sizeof(block));
-}
-
-/*
- * First we make sure we have POOL_MIN_BITS of entropy in the pool, and then we
- * set the entropy count to zero (but don't actually touch any data). Only then
- * can we extract a new key with extract_entropy().
- */
-static bool drain_entropy(void *buf, size_t nbytes)
-{
- unsigned int entropy_count;
- do {
- entropy_count = READ_ONCE(input_pool.entropy_count);
- if (entropy_count < POOL_MIN_BITS)
- return false;
- } while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count);
- extract_entropy(buf, nbytes);
- wake_up_interruptible(&random_write_wait);
- kill_fasync(&fasync, SIGIO, POLL_OUT);
- return true;
-}
-
/*
* Each time the timer fires, we expect that we got an unpredictable
* jump in the cycle counter. Even if the timer is running on another

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