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random: credit architectural init the exact amount
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RDRAND and RDSEED can fail sometimes, which is fine. We currently
initialize the RNG with 512 bits of RDRAND/RDSEED. We only need 256 bits
of those to succeed in order to initialize the RNG. Instead of the
current "all or nothing" approach, actually credit these contributions
the amount that is actually contributed.

Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
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zx2c4 committed May 18, 2022
1 parent 2f14062 commit 12e45a2
Showing 1 changed file with 6 additions and 6 deletions.
12 changes: 6 additions & 6 deletions drivers/char/random.c
Original file line number Diff line number Diff line change
Expand Up @@ -927,21 +927,21 @@ static struct notifier_block pm_notifier = { .notifier_call = random_pm_notifica
*/
int __init random_init(const char *command_line)
{
size_t i;
ktime_t now = ktime_get_real();
bool arch_init = true;
unsigned int i, arch_bytes;
unsigned long rv;

#if defined(LATENT_ENTROPY_PLUGIN)
static const u8 compiletime_seed[BLAKE2S_BLOCK_SIZE] __initconst __latent_entropy;
_mix_pool_bytes(compiletime_seed, sizeof(compiletime_seed));
#endif

for (i = 0; i < BLAKE2S_BLOCK_SIZE; i += sizeof(rv)) {
for (i = 0, arch_bytes = BLAKE2S_BLOCK_SIZE;
i < BLAKE2S_BLOCK_SIZE; i += sizeof(rv)) {
if (!arch_get_random_seed_long_early(&rv) &&
!arch_get_random_long_early(&rv)) {
rv = random_get_entropy();
arch_init = false;
arch_bytes -= sizeof(rv);
}
_mix_pool_bytes(&rv, sizeof(rv));
}
Expand All @@ -952,8 +952,8 @@ int __init random_init(const char *command_line)

if (crng_ready())
crng_reseed();
else if (arch_init && trust_cpu)
credit_init_bits(BLAKE2S_BLOCK_SIZE * 8);
else if (trust_cpu)
credit_init_bits(arch_bytes * 8);

WARN_ON(register_pm_notifier(&pm_notifier));

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