Fix issues in ia32 RDRAND asm leading to reduced entropy
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)
2018-03-07 21:01:06 +00:00
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#! /usr/bin/perl
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2018-03-20 13:00:17 +00:00
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# Copyright 2018 The OpenSSL Project Authors. All Rights Reserved.
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Fix issues in ia32 RDRAND asm leading to reduced entropy
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)
2018-03-07 21:01:06 +00:00
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#
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# Licensed under the OpenSSL license (the "License"). You may not use
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# this file except in compliance with the License. You can obtain a copy
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# in the file LICENSE in the source distribution or at
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# https://www.openssl.org/source/license.html
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use strict;
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use OpenSSL::Test; # get 'plan'
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use OpenSSL::Test::Simple;
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use OpenSSL::Test::Utils;
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setup("test_rdrand_sanity");
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plan skip_all => "This test is unsupported in a shared library build on Windows"
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if $^O eq 'MSWin32' && !disabled("shared");
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# We also need static builds to be enabled even on linux
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plan skip_all => "This test is unsupported if static builds are not enabled"
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if disabled("static");
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simple_test("test_rdrand_sanity", "rdrand_sanitytest");
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