[PATCH 5.4 146/240] random: do not use batches when !crng_ready()

Greg Kroah-Hartman
2022-06-20T13:52:45Z

commit cbe89e5a375a51bbb952929b93fa973416fea74e upstream.

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>
Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/char/random.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -465,10 +465,8 @@ static void crng_pre_init_inject(const v

if (account) {
crng_init_cnt += min_t(size_t, len, CRNG_INIT_CNT_THRESH - crng_init_cnt);
- if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) {
- ++base_crng.generation;
+ if (crng_init_cnt >= CRNG_INIT_CNT_THRESH)
crng_init = 1;
- }
}

spin_unlock_irqrestore(&base_crng.lock, flags);
@@ -622,6 +620,11 @@ u64 get_random_u64(void)

warn_unseeded_randomness(&previous);

+ if (!crng_ready()) {
+ _get_random_bytes(&ret, sizeof(ret));
+ return ret;
+ }
+
local_irq_save(flags);
batch = raw_cpu_ptr(&batched_entropy_u64);

@@ -655,6 +658,11 @@ u32 get_random_u32(void)

warn_unseeded_randomness(&previous);

+ if (!crng_ready()) {
+ _get_random_bytes(&ret, sizeof(ret));
+ return ret;
+ }
+
local_irq_save(flags);
batch = raw_cpu_ptr(&batched_entropy_u32);