The patch below does not apply to the 5.17-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From af704c856e888fb044b058d731d61b46eeec499d Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Jason@zx2c4.com Date: Mon, 21 Mar 2022 18:48:05 -0600 Subject: [PATCH] random: skip fast_init if hwrng provides large chunk of entropy
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 linux@dominikbrodowski.net Signed-off-by: Jason A. Donenfeld Jason@zx2c4.com
diff --git a/drivers/char/random.c b/drivers/char/random.c index 66ce7c03a142..74e0b069972e 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1128,7 +1128,7 @@ 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;