From: Jason A. Donenfeld Jason@zx2c4.com
[ Upstream commit 73c7733f122e8d0107f88655a12011f68f69e74b ]
When crng_fast_load() is called by add_hwgenerator_randomness(), we currently will advance to crng_init==1 once we've acquired 64 bytes, and then throw away the rest of the buffer. Usually, that is not a problem: When add_hwgenerator_randomness() gets called via EFI or DT during setup_arch(), there won't be any IRQ randomness. Therefore, the 64 bytes passed by EFI exactly matches what is needed to advance to crng_init==1. Usually, DT seems to pass 64 bytes as well -- with one notable exception being kexec, which hands over 128 bytes of entropy to the kexec'd kernel. In that case, we'll advance to crng_init==1 once 64 of those bytes are consumed by crng_fast_load(), but won't continue onward feeding in bytes to progress to crng_init==2. This commit fixes the issue by feeding any leftover bytes into the next phase in add_hwgenerator_randomness().
[linux@dominikbrodowski.net: rewrite commit message] Signed-off-by: Dominik Brodowski linux@dominikbrodowski.net Signed-off-by: Jason A. Donenfeld Jason@zx2c4.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/char/random.c | 19 ++++++++++++------- 1 file changed, 12 insertions(+), 7 deletions(-)
diff --git a/drivers/char/random.c b/drivers/char/random.c index 7470ee24db2f9..a27ae3999ff32 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -912,12 +912,14 @@ static struct crng_state *select_crng(void)
/* * crng_fast_load() can be called by code in the interrupt service - * path. So we can't afford to dilly-dally. + * path. So we can't afford to dilly-dally. Returns the number of + * bytes processed from cp. */ -static int crng_fast_load(const char *cp, size_t len) +static size_t crng_fast_load(const char *cp, size_t len) { unsigned long flags; char *p; + size_t ret = 0;
if (!spin_trylock_irqsave(&primary_crng.lock, flags)) return 0; @@ -928,7 +930,7 @@ static int crng_fast_load(const char *cp, size_t len) p = (unsigned char *) &primary_crng.state[4]; while (len > 0 && crng_init_cnt < CRNG_INIT_CNT_THRESH) { p[crng_init_cnt % CHACHA_KEY_SIZE] ^= *cp; - cp++; crng_init_cnt++; len--; + cp++; crng_init_cnt++; len--; ret++; } spin_unlock_irqrestore(&primary_crng.lock, flags); if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) { @@ -936,7 +938,7 @@ static int crng_fast_load(const char *cp, size_t len) crng_init = 1; pr_notice("fast init done\n"); } - return 1; + return ret; }
/* @@ -1287,7 +1289,7 @@ void add_interrupt_randomness(int irq, int irq_flags) if (unlikely(crng_init == 0)) { if ((fast_pool->count >= 64) && crng_fast_load((char *) fast_pool->pool, - sizeof(fast_pool->pool))) { + sizeof(fast_pool->pool)) > 0) { fast_pool->count = 0; fast_pool->last = now; } @@ -2295,8 +2297,11 @@ void add_hwgenerator_randomness(const char *buffer, size_t count, struct entropy_store *poolp = &input_pool;
if (unlikely(crng_init == 0)) { - crng_fast_load(buffer, count); - return; + size_t ret = crng_fast_load(buffer, count); + count -= ret; + buffer += ret; + if (!count || crng_init == 0) + return; }
/* Suspend writing if we're above the trickle threshold.