random: credit architectural init the exact amount

stable inclusion
from stable-v5.10.119
commit 04d61b96bd8a97755d416fbbe07b4ba8bffba564
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5L6BB

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=04d61b96bd8a97755d416fbbe07b4ba8bffba564

--------------------------------

commit 12e45a2a 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: NDominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: NJason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>
Acked-by: NXie XiuQi <xiexiuqi@huawei.com>

drivers/char/random.c

@@ -896,9 +896,8 @@ 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)
@@ -906,11 +905,12 @@ 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));
 	}
@@ -921,8 +921,8 @@ 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;
 }