linux-kernel - [PATCH v8 2/7] random: do not re-init if crng

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Message-Id: <20211229211009.108091-2-linux@dominikbrodowski.net>
Date:   Wed, 29 Dec 2021 22:10:04 +0100
From:   Dominik Brodowski <linux@...inikbrodowski.net>
To:     "Jason A . Donenfeld" <Jason@...c4.com>
Cc:     linux-kernel@...r.kernel.org, Theodore Ts'o <tytso@....edu>,
        "Ivan T . Ivanov" <iivanov@...e.de>,
        Ard Biesheuvel <ardb@...nel.org>, linux-efi@...r.kernel.org,
        linux@...inikbrodowski.net
Subject: [PATCH v8 2/7] random: do not re-init if crng_reseed completes before primary init

From: "Jason A. Donenfeld" <Jason@...c4.com>

If the bootloader supplies sufficient material and crng_reseed() is called
very early on, but not too early that wqs aren't available yet, then we
might transition to crng_init==2 before rand_initialize()'s call to
crng_initialize_primary() made. Then, when crng_initialize_primary() is
called, if we're trusting the CPU's RDRAND instructions, we'll
needlessly reinitialize the RNG and emit a message about it. This is
mostly harmless, as numa_crng_init() will allocate and then free what it
just allocated, and excessive calls to invalidate_batched_entropy()
aren't so harmful. But it is funky and the extra message is confusing,
so avoid the re-initialization all together by checking for crng_init <
2 in crng_initialize_primary(), just as we already do in crng_reseed().

Reviewed-by: Dominik Brodowski <linux@...inikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
---
 drivers/char/random.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 144e8841bff4..916cf791ed0e 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -827,7 +827,7 @@ static void __init crng_initialize_primary(struct crng_state *crng)
 {
 	chacha_init_consts(crng->state);
 	_extract_entropy(&input_pool, &crng->state[4], sizeof(__u32) * 12, 0);
-	if (crng_init_try_arch_early(crng) && trust_cpu) {
+	if (crng_init_try_arch_early(crng) && trust_cpu && crng_init < 2) {
 		invalidate_batched_entropy();
 		numa_crng_init();
 		crng_init = 2;
-- 
2.34.1