From 7c068998bac3e4a254d8542458b2068e38fca435 Mon Sep 17 00:00:00 2001 From: Pieter Wuille Date: Wed, 12 Aug 2020 15:52:20 -0700 Subject: [PATCH] Compile-time check assumptions on integer types --- Makefile.am | 1 + src/assumptions.h | 74 +++++++++++++++++++++++++++++++++++++++ src/bench_internal.c | 1 + src/gen_context.c | 1 + src/secp256k1.c | 1 + src/tests_exhaustive.c | 1 + src/valgrind_ctime_test.c | 1 + 7 files changed, 80 insertions(+) create mode 100644 src/assumptions.h diff --git a/Makefile.am b/Makefile.am index a30a84cd599c7..1c19e14debb91 100644 --- a/Makefile.am +++ b/Makefile.am @@ -34,6 +34,7 @@ noinst_HEADERS += src/field_5x52.h noinst_HEADERS += src/field_5x52_impl.h noinst_HEADERS += src/field_5x52_int128_impl.h noinst_HEADERS += src/field_5x52_asm_impl.h +noinst_HEADERS += src/assumptions.h noinst_HEADERS += src/util.h noinst_HEADERS += src/scratch.h noinst_HEADERS += src/scratch_impl.h diff --git a/src/assumptions.h b/src/assumptions.h new file mode 100644 index 0000000000000..f9d4e8e793516 --- /dev/null +++ b/src/assumptions.h @@ -0,0 +1,74 @@ +/********************************************************************** + * Copyright (c) 2020 Pieter Wuille * + * Distributed under the MIT software license, see the accompanying * + * file COPYING or http://www.opensource.org/licenses/mit-license.php.* + **********************************************************************/ + +#ifndef SECP256K1_ASSUMPTIONS_H +#define SECP256K1_ASSUMPTIONS_H + +#include "util.h" + +/* This library, like most software, relies on a number of compiler implementation defined (but not undefined) + behaviours. Although the behaviours we require are essentially universal we test them specifically here to + reduce the odds of experiencing an unwelcome surprise. +*/ + +struct secp256k1_assumption_checker { + /* This uses a trick to implement a static assertion in C89: a type with an array of negative size is not + allowed. */ + int dummy_array[( + /* Bytes are 8 bits. */ + CHAR_BIT == 8 && + + /* Conversions from unsigned to signed outside of the bounds of the signed type are + implementation-defined. Verify that they function as reinterpreting the lower + bits of the input in two's complement notation. Do this for conversions: + - from uint(N)_t to int(N)_t with negative result + - from uint(2N)_t to int(N)_t with negative result + - from int(2N)_t to int(N)_t with negative result + - from int(2N)_t to int(N)_t with positive result */ + + /* To int8_t. */ + ((int8_t)(uint8_t)0xAB == (int8_t)-(int8_t)0x55) && + ((int8_t)(uint16_t)0xABCD == (int8_t)-(int8_t)0x33) && + ((int8_t)(int16_t)(uint16_t)0xCDEF == (int8_t)(uint8_t)0xEF) && + ((int8_t)(int16_t)(uint16_t)0x9234 == (int8_t)(uint8_t)0x34) && + + /* To int16_t. */ + ((int16_t)(uint16_t)0xBCDE == (int16_t)-(int16_t)0x4322) && + ((int16_t)(uint32_t)0xA1B2C3D4 == (int16_t)-(int16_t)0x3C2C) && + ((int16_t)(int32_t)(uint32_t)0xC1D2E3F4 == (int16_t)(uint16_t)0xE3F4) && + ((int16_t)(int32_t)(uint32_t)0x92345678 == (int16_t)(uint16_t)0x5678) && + + /* To int32_t. */ + ((int32_t)(uint32_t)0xB2C3D4E5 == (int32_t)-(int32_t)0x4D3C2B1B) && + ((int32_t)(uint64_t)0xA123B456C789D012ULL == (int32_t)-(int32_t)0x38762FEE) && + ((int32_t)(int64_t)(uint64_t)0xC1D2E3F4A5B6C7D8ULL == (int32_t)(uint32_t)0xA5B6C7D8) && + ((int32_t)(int64_t)(uint64_t)0xABCDEF0123456789ULL == (int32_t)(uint32_t)0x23456789) && + + /* To int64_t. */ + ((int64_t)(uint64_t)0xB123C456D789E012ULL == (int64_t)-(int64_t)0x4EDC3BA928761FEEULL) && +#if defined(SECP256K1_WIDEMUL_INT128) + ((int64_t)(((uint128_t)0xA1234567B8901234ULL << 64) + 0xC5678901D2345678ULL) == (int64_t)-(int64_t)0x3A9876FE2DCBA988ULL) && + (((int64_t)(int128_t)(((uint128_t)0xB1C2D3E4F5A6B7C8ULL << 64) + 0xD9E0F1A2B3C4D5E6ULL)) == (int64_t)(uint64_t)0xD9E0F1A2B3C4D5E6ULL) && + (((int64_t)(int128_t)(((uint128_t)0xABCDEF0123456789ULL << 64) + 0x0123456789ABCDEFULL)) == (int64_t)(uint64_t)0x0123456789ABCDEFULL) && + + /* To int128_t. */ + ((int128_t)(((uint128_t)0xB1234567C8901234ULL << 64) + 0xD5678901E2345678ULL) == (int128_t)(-(int128_t)0x8E1648B3F50E80DCULL * 0x8E1648B3F50E80DDULL + 0x5EA688D5482F9464ULL)) && +#endif + + /* Right shift on negative signed values is implementation defined. Verify that it + acts as a right shift in two's complement with sign extension (i.e duplicating + the top bit into newly added bits). */ + ((((int8_t)0xE8) >> 2) == (int8_t)(uint8_t)0xFA) && + ((((int16_t)0xE9AC) >> 4) == (int16_t)(uint16_t)0xFE9A) && + ((((int32_t)0x937C918A) >> 9) == (int32_t)(uint32_t)0xFFC9BE48) && + ((((int64_t)0xA8B72231DF9CF4B9ULL) >> 19) == (int64_t)(uint64_t)0xFFFFF516E4463BF3ULL) && +#if defined(SECP256K1_WIDEMUL_INT128) + ((((int128_t)(((uint128_t)0xCD833A65684A0DBCULL << 64) + 0xB349312F71EA7637ULL)) >> 39) == (int128_t)(((uint128_t)0xFFFFFFFFFF9B0674ULL << 64) + 0xCAD0941B79669262ULL)) && +#endif + 1) * 2 - 1]; +}; + +#endif /* SECP256K1_ASSUMPTIONS_H */ diff --git a/src/bench_internal.c b/src/bench_internal.c index 20759127d3c9f..cb8368ddff628 100644 --- a/src/bench_internal.c +++ b/src/bench_internal.c @@ -7,6 +7,7 @@ #include "include/secp256k1.h" +#include "assumptions.h" #include "util.h" #include "hash_impl.h" #include "num_impl.h" diff --git a/src/gen_context.c b/src/gen_context.c index 539f574bfd0c6..8b7729aee4c8d 100644 --- a/src/gen_context.c +++ b/src/gen_context.c @@ -13,6 +13,7 @@ #include "basic-config.h" #include "include/secp256k1.h" +#include "assumptions.h" #include "util.h" #include "field_impl.h" #include "scalar_impl.h" diff --git a/src/secp256k1.c b/src/secp256k1.c index 3e7926503825d..b43a9592eb63d 100644 --- a/src/secp256k1.c +++ b/src/secp256k1.c @@ -7,6 +7,7 @@ #include "include/secp256k1.h" #include "include/secp256k1_preallocated.h" +#include "assumptions.h" #include "util.h" #include "num_impl.h" #include "field_impl.h" diff --git a/src/tests_exhaustive.c b/src/tests_exhaustive.c index 8f346701aa7af..681ed80bd0bc4 100644 --- a/src/tests_exhaustive.c +++ b/src/tests_exhaustive.c @@ -22,6 +22,7 @@ #endif #include "include/secp256k1.h" +#include "assumptions.h" #include "group.h" #include "secp256k1.c" #include "testrand_impl.h" diff --git a/src/valgrind_ctime_test.c b/src/valgrind_ctime_test.c index 60a82d599e8f9..090fde2b6e495 100644 --- a/src/valgrind_ctime_test.c +++ b/src/valgrind_ctime_test.c @@ -6,6 +6,7 @@ #include #include "include/secp256k1.h" +#include "assumptions.h" #include "util.h" #if ENABLE_MODULE_ECDH