// Copyright 2017 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// HERMETIC NOTE: The randen_hwaes target must not introduce duplicate
// symbols from arbitrary system and other headers, since it may be built
// with different flags from other targets, using different levels of
// optimization, potentially introducing ODR violations.
#include "absl/random/internal/randen_detect.h"
#include <cstdint>
#include <cstring>
#include "absl/random/internal/platform.h"
#if defined(ABSL_ARCH_X86_64)
#define ABSL_INTERNAL_USE_X86_CPUID
#elif defined(ABSL_ARCH_PPC) || defined(ABSL_ARCH_ARM) || \
defined(ABSL_ARCH_AARCH64)
#if defined(__ANDROID__)
#define ABSL_INTERNAL_USE_ANDROID_GETAUXVAL
#define ABSL_INTERNAL_USE_GETAUXVAL
#elif defined(__linux__)
#define ABSL_INTERNAL_USE_LINUX_GETAUXVAL
#define ABSL_INTERNAL_USE_GETAUXVAL
#endif
#endif
#if defined(ABSL_INTERNAL_USE_X86_CPUID)
#if defined(_WIN32) || defined(_WIN64)
#include <intrin.h> // NOLINT(build/include_order)
#pragma intrinsic(__cpuid)
#else
// MSVC-equivalent __cpuid intrinsic function.
static void __cpuid(int cpu_info[4], int info_type) {
__asm__ volatile("cpuid \n\t"
: "=a"(cpu_info[0]), "=b"(cpu_info[1]), "=c"(cpu_info[2]),
"=d"(cpu_info[3])
: "a"(info_type), "c"(0));
}
#endif
#endif // ABSL_INTERNAL_USE_X86_CPUID
// On linux, just use the c-library getauxval call.
#if defined(ABSL_INTERNAL_USE_LINUX_GETAUXVAL)
extern "C" unsigned long getauxval(unsigned long type); // NOLINT(runtime/int)
static uint32_t GetAuxval(uint32_t hwcap_type) {
return static_cast<uint32_t>(getauxval(hwcap_type));
}
#endif
// On android, probe the system's C library for getauxval().
// This is the same technique used by the android NDK cpu features library
// as well as the google open-source cpu_features library.
//
// TODO(absl-team): Consider implementing a fallback of directly reading
// /proc/self/auxval.
#if defined(ABSL_INTERNAL_USE_ANDROID_GETAUXVAL)
#include <dlfcn.h>
static uint32_t GetAuxval(uint32_t hwcap_type) {
// NOLINTNEXTLINE(runtime/int)
typedef unsigned long (*getauxval_func_t)(unsigned long);
dlerror(); // Cleaning error state before calling dlopen.
void* libc_handle = dlopen("libc.so", RTLD_NOW);
if (!libc_handle) {
return 0;
}
uint32_t result = 0;
void* sym = dlsym(libc_handle, "getauxval");
if (sym) {
getauxval_func_t func;
memcpy(&func, &sym, sizeof(func));
result = static_cast<uint32_t>((*func)(hwcap_type));
}
dlclose(libc_handle);
return result;
}
#endif
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace random_internal {
// The default return at the end of the function might be unreachable depending
// on the configuration. Ignore that warning.
#if defined(__clang__)
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wunreachable-code-return"
#endif
// CPUSupportsRandenHwAes returns whether the CPU is a microarchitecture
// which supports the crpyto/aes instructions or extensions necessary to use the
// accelerated RandenHwAes implementation.
//
// 1. For x86 it is sufficient to use the CPUID instruction to detect whether
// the cpu supports AES instructions. Done.
//
// Fon non-x86 it is much more complicated.
//
// 2. When ABSL_INTERNAL_USE_GETAUXVAL is defined, use getauxval() (either
// the direct c-library version, or the android probing version which loads
// libc), and read the hardware capability bits.
// This is based on the technique used by boringssl uses to detect
// cpu capabilities, and should allow us to enable crypto in the android
// builds where it is supported.
//
// 3. Use the default for the compiler architecture.
//
bool CPUSupportsRandenHwAes() {
#if defined(ABSL_INTERNAL_USE_X86_CPUID)
// 1. For x86: Use CPUID to detect the required AES instruction set.
int regs[4];
__cpuid(reinterpret_cast<int*>(regs), 1);
return regs[2] & (1 << 25); // AES
#elif defined(ABSL_INTERNAL_USE_GETAUXVAL)
// 2. Use getauxval() to read the hardware bits and determine
// cpu capabilities.
#define AT_HWCAP 16
#define AT_HWCAP2 26
#if defined(ABSL_ARCH_PPC)
// For Power / PPC: Expect that the cpu supports VCRYPTO
// See https://members.openpowerfoundation.org/document/dl/576
// VCRYPTO should be present in POWER8 >= 2.07.
// Uses Linux kernel constants from arch/powerpc/include/uapi/asm/cputable.h
static const uint32_t kVCRYPTO = 0x02000000;
const uint32_t hwcap = GetAuxval(AT_HWCAP2);
return (hwcap & kVCRYPTO) != 0;
#elif defined(ABSL_ARCH_ARM)
// For ARM: Require crypto+neon
// http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0500f/CIHBIBBA.html
// Uses Linux kernel constants from arch/arm64/include/asm/hwcap.h
static const uint32_t kNEON = 1 << 12;
uint32_t hwcap = GetAuxval(AT_HWCAP);
if ((hwcap & kNEON) == 0) {
return false;
}
// And use it again to detect AES.
static const uint32_t kAES = 1 << 0;
const uint32_t hwcap2 = GetAuxval(AT_HWCAP2);
return (hwcap2 & kAES) != 0;
#elif defined(ABSL_ARCH_AARCH64)
// For AARCH64: Require crypto+neon
// http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0500f/CIHBIBBA.html
static const uint32_t kNEON = 1 << 1;
static const uint32_t kAES = 1 << 3;
const uint32_t hwcap = GetAuxval(AT_HWCAP);
return ((hwcap & kNEON) != 0) && ((hwcap & kAES) != 0);
#endif
#else // ABSL_INTERNAL_USE_GETAUXVAL
// 3. By default, assume that the compiler default.
return ABSL_HAVE_ACCELERATED_AES ? true : false;
#endif
// NOTE: There are some other techniques that may be worth trying:
//
// * Use an environment variable: ABSL_RANDOM_USE_HWAES
//
// * Rely on compiler-generated target-based dispatch.
// Using x86/gcc it might look something like this:
//
// int __attribute__((target("aes"))) HasAes() { return 1; }
// int __attribute__((target("default"))) HasAes() { return 0; }
//
// This does not work on all architecture/compiler combinations.
//
// * On Linux consider reading /proc/cpuinfo and/or /proc/self/auxv.
// These files have lines which are easy to parse; for ARM/AARCH64 it is quite
// easy to find the Features: line and extract aes / neon. Likewise for
// PPC.
//
// * Fork a process and test for SIGILL:
//
// * Many architectures have instructions to read the ISA. Unfortunately
// most of those require that the code is running in ring 0 /
// protected-mode.
//
// There are several examples. e.g. Valgrind detects PPC ISA 2.07:
// https://github.com/lu-zero/valgrind/blob/master/none/tests/ppc64/test_isa_2_07_part1.c
//
// MRS <Xt>, ID_AA64ISAR0_EL1 ; Read ID_AA64ISAR0_EL1 into Xt
//
// uint64_t val;
// __asm __volatile("mrs %0, id_aa64isar0_el1" :"=&r" (val));
//
// * Use a CPUID-style heuristic database.
//
// * On Apple (__APPLE__), AES is available on Arm v8.
// https://stackoverflow.com/questions/45637888/how-to-determine-armv8-features-at-runtime-on-ios
}
#if defined(__clang__)
#pragma clang diagnostic pop
#endif
} // namespace random_internal
ABSL_NAMESPACE_END
} // namespace absl
