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random: ensure early RDSEED goes through mixer on init

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Continuing the reasoning of "random: use RDSEED instead of RDRAND in
entropy extraction" from this series, at init time we also don't want to
be xoring RDSEED directly into the crng. Instead it's safer to put it
into our entropy collector and then re-extract it, so that it goes
through a hash function with preimage resistance. As a matter of hygiene,
we also order these now so that the RDSEED byte are hashed in first,
followed by the bytes that are likely more predictable (e.g. utsname()).

Cc: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
This commit is contained in:
Jason A. Donenfeld 2022-02-08 12:44:28 +01:00
parent 8566417221
commit a02cf3d0dd
1 changed files with 5 additions and 11 deletions
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16
drivers/char/random.c
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@ -1208,24 +1208,18 @@ int __init rand_initialize(void)
bool arch_init = true;
unsigned long rv;
mix_pool_bytes(&now, sizeof(now));
for (i = BLAKE2S_BLOCK_SIZE; i > 0; i -= sizeof(rv)) {
if (!arch_get_random_seed_long(&rv) &&
!arch_get_random_long(&rv))
rv = random_get_entropy();
mix_pool_bytes(&rv, sizeof(rv));
}
mix_pool_bytes(utsname(), sizeof(*(utsname())));
extract_entropy(&primary_crng.state[4], sizeof(u32) * 12);
for (i = 4; i < 16; i++) {
if (!arch_get_random_seed_long_early(&rv) &&
!arch_get_random_long_early(&rv)) {
rv = random_get_entropy();
arch_init = false;
}
primary_crng.state[i] ^= rv;
mix_pool_bytes(&rv, sizeof(rv));
}
mix_pool_bytes(&now, sizeof(now));
mix_pool_bytes(utsname(), sizeof(*(utsname())));
extract_entropy(&primary_crng.state[4], sizeof(u32) * 12);
if (arch_init && trust_cpu && crng_init < 2) {
invalidate_batched_entropy();
crng_init = 2;