random: credit architectural init the exact amount

commit 12e45a2a6308105469968951e6d563e8f4fea187 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/char/random.c b/drivers/char/random.c
index f53e8a9820d81e9b72fba86f84764f5df5b75a93..dbe363bc644a32558d9dc9cb1629e7455f8ce4ca 100644 (file)
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -891,9 +891,8 @@ early_param("random.trust_bootloader", parse_trust_bootloader);
  */
 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)
@@ -901,11 +900,12 @@ int __init random_init(const char *command_line)
        _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));
        }
@@ -916,8 +916,8 @@ 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);
 
        return 0;
 }