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From:   "Jason A. Donenfeld" <Jason@zx2c4.com>
To:     linux-kernel@vger.kernel, linux-crypto@vger.kernel.org
Cc:     "Jason A. Donenfeld" <Jason@zx2c4.com>,
        Theodore Ts'o <tytso@mit.edu>,
        Dominik Brodowski <linux@dominikbrodowski.net>
Subject: [PATCH] random: do not use batches when !crng_ready()
Date:   Tue,  3 May 2022 14:18:36 +0200
Message-Id: <20220503121836.522258-1-Jason@zx2c4.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

It's too hard to keep the batches synchronized, and pointless anyway,
since in !crng_ready(), we're updating the base_crng key really often,
where batching only hurts. So instead, if the crng isn't ready, just
call into get_random_bytes(). At this stage nothing is performance
critical anyhow.

Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 drivers/char/random.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 346c9b16a7f1..53b8237687ed 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -610,6 +610,11 @@ u64 get_random_u64(void)
 
 	warn_unseeded_randomness(&previous);
 
+	if  (!crng_ready()) {
+		_get_random_bytes(&ret, sizeof(ret));
+		return ret;
+	}
+
 	local_lock_irqsave(&batched_entropy_u64.lock, flags);
 	batch = raw_cpu_ptr(&batched_entropy_u64);
 
@@ -644,6 +649,11 @@ u32 get_random_u32(void)
 
 	warn_unseeded_randomness(&previous);
 
+	if  (!crng_ready()) {
+		_get_random_bytes(&ret, sizeof(ret));
+		return ret;
+	}
+
 	local_lock_irqsave(&batched_entropy_u32.lock, flags);
 	batch = raw_cpu_ptr(&batched_entropy_u32);
 
@@ -820,10 +830,8 @@ static void credit_entropy_bits(size_t nbits)
 
 	if (unlikely(crng_init == 0 && entropy_count >= POOL_FAST_INIT_BITS)) {
 		spin_lock_irqsave(&base_crng.lock, flags);
-		if (crng_init == 0) {
-			++base_crng.generation;
+		if (crng_init == 0)
 			crng_init = 1;
-		}
 		spin_unlock_irqrestore(&base_crng.lock, flags);
 	}
 
@@ -1029,7 +1037,6 @@ int __init rand_initialize(void)
 	_mix_pool_bytes(utsname(), sizeof(*(utsname())));
 
 	extract_entropy(base_crng.key, sizeof(base_crng.key));
-	++base_crng.generation;
 
 	if (arch_init && trust_cpu && !crng_ready()) {
 		crng_init = 2;
-- 
2.35.1