Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit b64adad8 authored by Jason A. Donenfeld's avatar Jason A. Donenfeld Committed by Greg Kroah-Hartman
Browse files

random: unify early init crng load accounting 



commit da792c6d5f59a76c10a310c5d4c93428fd18f996 upstream.

crng_fast_load() and crng_slow_load() have different semantics:

- crng_fast_load() xors and accounts with crng_init_cnt.
- crng_slow_load() hashes and doesn't account.

However add_hwgenerator_randomness() can afford to hash (it's called
from a kthread), and it should account. Additionally, ones that can
afford to hash don't need to take a trylock but can take a normal lock.
So, we combine these into one function, crng_pre_init_inject(), which
allows us to control these in a uniform way. This will make it simpler
later to simplify this all down when the time comes for that.

Cc: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: default avatarDominik Brodowski <linux@dominikbrodowski.net>
Reviewed-by: default avatarEric Biggers <ebiggers@google.com>
Signed-off-by: default avatarJason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent b195259c

drivers/char/random.c

+58 −54
Original line number Diff line number Diff line
@@ -385,7 +385,7 @@ static void crng_make_state(u32 chacha_state[CHACHA20_BLOCK_SIZE / sizeof(u32)], 
	 * For the fast path, we check whether we're ready, unlocked first, and

	 * then re-check once locked later. In the case where we're really not

	 * ready, we do fast key erasure with the base_crng directly, because

	 * this is what crng_{fast,slow}_load mutate during early init.

	 * this is what crng_pre_init_inject() mutates during early init.

	 */

	if (unlikely(!crng_ready())) {

		bool ready;
@@ -436,72 +436,75 @@ static void crng_make_state(u32 chacha_state[CHACHA20_BLOCK_SIZE / sizeof(u32)], 
}



/*

 * This function is for crng_init == 0 only.

 *

 * crng_fast_load() can be called by code in the interrupt service

 * path.  So we can't afford to dilly-dally. Returns the number of

 * bytes processed from cp.

 * This function is for crng_init == 0 only. It loads entropy directly

 * into the crng's key, without going through the input pool. It is,

 * generally speaking, not very safe, but we use this only at early

 * boot time when it's better to have something there rather than

 * nothing.

 *

 * There are two paths, a slow one and a fast one. The slow one

 * hashes the input along with the current key. The fast one simply

 * xors it in, and should only be used from interrupt context.

 *

 * If account is set, then the crng_init_cnt counter is incremented.

 * This shouldn't be set by functions like add_device_randomness(),

 * where we can't trust the buffer passed to it is guaranteed to be

 * unpredictable (so it might not have any entropy at all).

 *

 * Returns the number of bytes processed from input, which is bounded

 * by CRNG_INIT_CNT_THRESH if account is true.

 */

static size_t crng_fast_load(const void *cp, size_t len)

static size_t crng_pre_init_inject(const void *input, size_t len,

				   bool fast, bool account)

{

	static int crng_init_cnt = 0;

	unsigned long flags;

	const u8 *src = (const u8 *)cp;

	size_t ret = 0;



	if (fast) {

		if (!spin_trylock_irqsave(&base_crng.lock, flags))

			return 0;

	} else {

		spin_lock_irqsave(&base_crng.lock, flags);

	}



	if (crng_init != 0) {

		spin_unlock_irqrestore(&base_crng.lock, flags);

		return 0;

	}

	while (len > 0 && crng_init_cnt < CRNG_INIT_CNT_THRESH) {

		base_crng.key[crng_init_cnt % sizeof(base_crng.key)] ^= *src;

		src++; crng_init_cnt++; len--; ret++;



	if (account)

		len = min_t(size_t, len, CRNG_INIT_CNT_THRESH - crng_init_cnt);



	if (fast) {

		const u8 *src = input;

		size_t i;



		for (i = 0; i < len; ++i)

			base_crng.key[(crng_init_cnt + i) %

				      sizeof(base_crng.key)] ^= src[i];

	} else {

		struct blake2s_state hash;



		blake2s_init(&hash, sizeof(base_crng.key));

		blake2s_update(&hash, base_crng.key, sizeof(base_crng.key));

		blake2s_update(&hash, input, len);

		blake2s_final(&hash, base_crng.key);

	}



	if (account) {

		crng_init_cnt += len;

		if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) {

			++base_crng.generation;

			crng_init = 1;

		}

	spin_unlock_irqrestore(&base_crng.lock, flags);

	if (crng_init == 1)

		pr_notice("fast init done\n");

	return ret;

	}



/*

 * This function is for crng_init == 0 only.

 *

 * crng_slow_load() is called by add_device_randomness, which has two

 * attributes.  (1) We can't trust the buffer passed to it is

 * guaranteed to be unpredictable (so it might not have any entropy at

 * all), and (2) it doesn't have the performance constraints of

 * crng_fast_load().

 *

 * So, we simply hash the contents in with the current key. Finally,

 * we do *not* advance crng_init_cnt since buffer we may get may be

 * something like a fixed DMI table (for example), which might very

 * well be unique to the machine, but is otherwise unvarying.

 */

static void crng_slow_load(const void *cp, size_t len)

{

	unsigned long flags;

	struct blake2s_state hash;



	blake2s_init(&hash, sizeof(base_crng.key));



	if (!spin_trylock_irqsave(&base_crng.lock, flags))

		return;

	if (crng_init != 0) {

	spin_unlock_irqrestore(&base_crng.lock, flags);

		return;

	}



	blake2s_update(&hash, base_crng.key, sizeof(base_crng.key));

	blake2s_update(&hash, cp, len);

	blake2s_final(&hash, base_crng.key);

	if (crng_init == 1)

		pr_notice("fast init done\n");



	spin_unlock_irqrestore(&base_crng.lock, flags);

	return len;

}



static void _get_random_bytes(void *buf, size_t nbytes)
@@ -1014,7 +1017,7 @@ void add_device_randomness(const void *buf, size_t size) 
	unsigned long flags;



	if (!crng_ready() && size)

		crng_slow_load(buf, size);

		crng_pre_init_inject(buf, size, false, false);



	spin_lock_irqsave(&input_pool.lock, flags);

	_mix_pool_bytes(buf, size);
@@ -1131,7 +1134,7 @@ void add_hwgenerator_randomness(const void *buffer, size_t count, 
				size_t entropy)

{

	if (unlikely(crng_init == 0)) {

		size_t ret = crng_fast_load(buffer, count);

		size_t ret = crng_pre_init_inject(buffer, count, false, true);

		mix_pool_bytes(buffer, ret);

		count -= ret;

		buffer += ret;
@@ -1294,7 +1297,8 @@ void add_interrupt_randomness(int irq) 


	if (unlikely(crng_init == 0)) {

		if (new_count >= 64 &&

		    crng_fast_load(fast_pool->pool32, sizeof(fast_pool->pool32)) > 0) {

		    crng_pre_init_inject(fast_pool->pool32, sizeof(fast_pool->pool32),

					 true, true) > 0) {

			atomic_set(&fast_pool->count, 0);

			fast_pool->last = now;

			if (spin_trylock(&input_pool.lock)) {