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c998f74ae3
BCryptGenRandom can be broken, but the Rust stdlib and the getrandom crate rely on it, and this is a source of crashes which are Rust panics. This happens the most on Windows 7 after bcryptprimitives.dll fails to load (see bug 1788004). To mitigate these crashes, we hook BCryptGenRandom if we detect that it is broken, and install a fallback based on RtlGenRandom. We only protect calls that use BCRYPT_USE_SYSTEM_PREFERRED_RNG; so code that relies on using BCryptOpenAlgorithmProvider and doesn't have its own fallback can still fail. We will hopefully remove this hook when the Rust stdlib and the getrandom crate both have their own RtlGenRandom-based fallback. Differential Revision: https://phabricator.services.mozilla.com/D170662
149 lines
4.1 KiB
C++
149 lines
4.1 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at https://mozilla.org/MPL/2.0/. */
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#include "mozilla/RandomNum.h"
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#include <fcntl.h>
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#ifdef XP_UNIX
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# include <unistd.h>
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#endif
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#if defined(XP_WIN)
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// Microsoft doesn't "officially" support using RtlGenRandom() directly
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// anymore, and the Windows headers assume that __stdcall is
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// the default calling convention (which is true when Microsoft uses this
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// function to build their own CRT libraries).
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// We will explicitly declare it with the proper calling convention.
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# include "minwindef.h"
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# define RtlGenRandom SystemFunction036
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extern "C" BOOLEAN NTAPI RtlGenRandom(PVOID RandomBuffer,
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ULONG RandomBufferLength);
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#endif
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#if defined(ANDROID) || defined(XP_DARWIN) || defined(__DragonFly__) || \
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defined(__FreeBSD__) || defined(__NetBSD__) || defined(__OpenBSD__) || \
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defined(__wasi__)
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# include <stdlib.h>
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# define USE_ARC4RANDOM
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#endif
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#if defined(__linux__)
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# include <linux/random.h> // For GRND_NONBLOCK.
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# include <sys/syscall.h> // For SYS_getrandom.
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// Older glibc versions don't define SYS_getrandom, so we define it here if
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// it's not available. See bug 995069.
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# if defined(__x86_64__)
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# define GETRANDOM_NR 318
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# elif defined(__i386__)
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# define GETRANDOM_NR 355
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# elif defined(__aarch64__)
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# define GETRANDOM_NR 278
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# elif defined(__arm__)
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# define GETRANDOM_NR 384
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# elif defined(__powerpc__)
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# define GETRANDOM_NR 359
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# elif defined(__s390__)
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# define GETRANDOM_NR 349
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# elif defined(__mips__)
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# include <sgidefs.h>
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# if _MIPS_SIM == _MIPS_SIM_ABI32
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# define GETRANDOM_NR 4353
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# elif _MIPS_SIM == _MIPS_SIM_ABI64
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# define GETRANDOM_NR 5313
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# elif _MIPS_SIM == _MIPS_SIM_NABI32
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# define GETRANDOM_NR 6317
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# endif
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# endif
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# if defined(SYS_getrandom)
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// We have SYS_getrandom. Use it to check GETRANDOM_NR. Only do this if we set
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// GETRANDOM_NR so tier 3 platforms with recent glibc are not forced to define
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// it for no good reason.
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# if defined(GETRANDOM_NR)
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static_assert(GETRANDOM_NR == SYS_getrandom,
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"GETRANDOM_NR should match the actual SYS_getrandom value");
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# endif
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# else
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# define SYS_getrandom GETRANDOM_NR
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# endif
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# if defined(GRND_NONBLOCK)
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static_assert(GRND_NONBLOCK == 1,
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"If GRND_NONBLOCK is not 1 the #define below is wrong");
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# else
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# define GRND_NONBLOCK 1
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# endif
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#endif // defined(__linux__)
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namespace mozilla {
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MFBT_API bool GenerateRandomBytesFromOS(void* aBuffer, size_t aLength) {
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MOZ_ASSERT(aBuffer);
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MOZ_ASSERT(aLength > 0);
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#if defined(XP_WIN)
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// Note: This function is used as a fallback for BCryptGenRandom in
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// WindowsBCryptInitialization(). Do not use BCryptGenRandom here!
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return !!RtlGenRandom(aBuffer, aLength);
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#elif defined(USE_ARC4RANDOM) // defined(XP_WIN)
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arc4random_buf(aBuffer, aLength);
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return true;
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#elif defined(XP_UNIX) // defined(USE_ARC4RANDOM)
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# if defined(__linux__)
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long bytesGenerated = syscall(SYS_getrandom, aBuffer, aLength, GRND_NONBLOCK);
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if (static_cast<unsigned long>(bytesGenerated) == aLength) {
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return true;
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}
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// Fall-through to UNIX behavior if failed
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# endif // defined(__linux__)
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int fd = open("/dev/urandom", O_RDONLY);
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if (fd < 0) {
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return false;
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}
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ssize_t bytesRead = read(fd, aBuffer, aLength);
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close(fd);
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return (static_cast<size_t>(bytesRead) == aLength);
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#else // defined(XP_UNIX)
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# error "Platform needs to implement GenerateRandomBytesFromOS()"
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#endif
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}
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MFBT_API Maybe<uint64_t> RandomUint64() {
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uint64_t randomNum;
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if (!GenerateRandomBytesFromOS(&randomNum, sizeof(randomNum))) {
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return Nothing();
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}
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return Some(randomNum);
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}
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MFBT_API uint64_t RandomUint64OrDie() {
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uint64_t randomNum;
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MOZ_RELEASE_ASSERT(GenerateRandomBytesFromOS(&randomNum, sizeof(randomNum)));
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return randomNum;
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}
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} // namespace mozilla
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