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random: ensure early RDSEED goes through mixer on init

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commit a02cf3d0dd upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Jason A. Donenfeld 2022-02-08 12:44:28 +01:00 • committed by Greg Kroah-Hartman
commit 16a6e4ae71
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;