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 c7b3256c543b134a660a468fa808e7ae95449209..092b31354cf3d8d045ed74644de6028f4d6651fb 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;