From: Jason A. Donenfeld Date: Tue, 22 Mar 2022 00:48:05 +0000 (-0600) Subject: random: skip fast_init if hwrng provides large chunk of entropy X-Git-Tag: v5.15.73~4030 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=a704248b4590ce5738360935ea688e7369c4ed6f;p=platform%2Fkernel%2Flinux-rpi.git random: skip fast_init if hwrng provides large chunk of entropy commit af704c856e888fb044b058d731d61b46eeec499d upstream. At boot time, EFI calls add_bootloader_randomness(), which in turn calls add_hwgenerator_randomness(). Currently add_hwgenerator_randomness() feeds the first 64 bytes of randomness to the "fast init" non-crypto-grade phase. But if add_hwgenerator_randomness() gets called with more than POOL_MIN_BITS of entropy, there's no point in passing it off to the "fast init" stage, since that's enough entropy to bootstrap the real RNG. The "fast init" stage is just there to provide _something_ in the case where we don't have enough entropy to properly bootstrap the RNG. But if we do have enough entropy to bootstrap the RNG, the current logic doesn't serve a purpose. So, in the case where we're passed greater than or equal to POOL_MIN_BITS of entropy, this commit makes us skip the "fast init" phase. Cc: Dominik Brodowski Signed-off-by: Jason A. Donenfeld Signed-off-by: Greg Kroah-Hartman --- diff --git a/drivers/char/random.c b/drivers/char/random.c index 4c0a12c..382ff01 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1125,7 +1125,7 @@ void rand_initialize_disk(struct gendisk *disk) void add_hwgenerator_randomness(const void *buffer, size_t count, size_t entropy) { - if (unlikely(crng_init == 0)) { + if (unlikely(crng_init == 0 && entropy < POOL_MIN_BITS)) { size_t ret = crng_pre_init_inject(buffer, count, true); mix_pool_bytes(buffer, ret); count -= ret;