From: "Jason A. Donenfeld" Jason@zx2c4.com
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: Dominik Brodowski linux@dominikbrodowski.net Reviewed-by: Eric Biggers ebiggers@google.com Signed-off-by: Jason A. Donenfeld Jason@zx2c4.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/char/random.c | 114 +++++++++++++++++++++++++------------------------- 1 file changed, 59 insertions(+), 55 deletions(-)
--- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -385,7 +385,7 @@ static void crng_make_state(u32 chacha_s * 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_s }
/* - * This function is for crng_init == 0 only. + * 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). * - * 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. + * 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 (!spin_trylock_irqsave(&base_crng.lock, flags)) - return 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 (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; + if (account) + len = min_t(size_t, len, CRNG_INIT_CNT_THRESH - crng_init_cnt);
- 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; + 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; + } }
- blake2s_update(&hash, base_crng.key, sizeof(base_crng.key)); - blake2s_update(&hash, cp, len); - blake2s_final(&hash, base_crng.key); - spin_unlock_irqrestore(&base_crng.lock, flags); + + if (crng_init == 1) + pr_notice("fast init done\n"); + + return len; }
static void _get_random_bytes(void *buf, size_t nbytes) @@ -1014,7 +1017,7 @@ void add_device_randomness(const void *b 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 vo 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)) {