random: ensure early RDSEED goes through mixer on init

commit a02cf3d0dd77244fd5333ac48d78871de459ae6d 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>

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 2b655f1fbf8c35fff8088599d1b7364c48daa0b8..f3e16bf620d4faf5269533d4c3fbe18263cc8f67 100644 (file)
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -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;