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Subject[PATCH v2] random: mix build-time latent entropy into pool at init
Prior, the "input_pool_data" array needed no real initialization, and so
it was easy to mark it with __latent_entropy to populate it during
compile-time. In switching to using a hash function, this required us to
specifically initialize it to some specific state, which means we
dropped the __latent_entropy attribute. An unfortunate side effect was
this meant the pool was no longer seeded using compile-time random data.
In order to bring this back, we declare an array in rand_initialize()
with __latent_entropy and call mix_pool_bytes() on that at init, which
accomplishes the same thing as before. We make this __initconst, so that
it doesn't take up space at runtime after init.

Fixes: 6e8ec2552c7d ("random: use computational hash for entropy extraction")
Cc: Dominik Brodowski <>
Cc: Theodore Ts'o <>
Signed-off-by: Jason A. Donenfeld <>
Changes v1->v2:
- Use __initconst.

drivers/char/random.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 40107f8b9e9e..1d8242969751 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -975,6 +975,11 @@ int __init rand_initialize(void)
bool arch_init = true;
unsigned long rv;

+ static const u8 compiletime_seed[BLAKE2S_BLOCK_SIZE] __initconst __latent_entropy;
+ _mix_pool_bytes(compiletime_seed, sizeof(compiletime_seed));
for (i = 0; i < BLAKE2S_BLOCK_SIZE; i += sizeof(rv)) {
if (!arch_get_random_seed_long_early(&rv) &&
!arch_get_random_long_early(&rv)) {
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