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082193ef2b
This patch fixes two issues in the ia32 RDRAND assembly code that result in a (possibly significant) loss of entropy. The first, less significant, issue is that, by returning success as 0 from OPENSSL_ia32_rdrand() and OPENSSL_ia32_rdseed(), a subtle bias was introduced. Specifically, because the assembly routine copied the remaining number of retries over the result when RDRAND/RDSEED returned 'successful but zero', a bias towards values 1-8 (primarily 8) was introduced. The second, more worrying issue was that, due to a mixup in registers, when a buffer that was not size 0 or 1 mod 8 was passed to OPENSSL_ia32_rdrand_bytes or OPENSSL_ia32_rdseed_bytes, the last (n mod 8) bytes were all the same value. This issue impacts only the 64-bit variant of the assembly. This change fixes both issues by first eliminating the only use of OPENSSL_ia32_rdrand, replacing it with OPENSSL_ia32_rdrand_bytes, and fixes the register mixup in OPENSSL_ia32_rdrand_bytes. It also adds a sanity test for OPENSSL_ia32_rdrand_bytes and OPENSSL_ia32_rdseed_bytes to help catch problems of this nature in the future. Reviewed-by: Andy Polyakov <appro@openssl.org> Reviewed-by: Rich Salz <rsalz@openssl.org> (Merged from https://github.com/openssl/openssl/pull/5342)