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Detect cpu features on ARM with getauxval()
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@marshallpierce
marshallpierce committed Jan 14, 2017
1 parent c431705 commit ddddb02
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377 changes: 32 additions & 345 deletions crypto/cpu-arm-linux.c
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/* Copyright (c) 2016, Google Inc.
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
* SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
* OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
* CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */

#include <openssl/cpu.h>

#if defined(OPENSSL_ARM) && !defined(OPENSSL_STATIC_ARMCAP)

#include <errno.h>
#include <fcntl.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>

#include <openssl/arm_arch.h>
#include <openssl/mem.h>

#include "internal.h"


#define AT_HWCAP 16
#define AT_HWCAP2 26

#define HWCAP_NEON (1 << 12)

/* See /usr/include/asm/hwcap.h on an ARM installation for the source of
* these values. */
#define HWCAP2_AES (1 << 0)
#define HWCAP2_PMULL (1 << 1)
#define HWCAP2_SHA1 (1 << 2)
#define HWCAP2_SHA2 (1 << 3)
#ifdef __linux__

/* |getauxval| is not available on Android until API level 20. Link it as a weak
* symbol and use other methods as fallback. */
* symbol and use other methods as fallback. As of Rust 1.14 this weak linkage
* isn't supported, so we do it in C.
*/
unsigned long getauxval(unsigned long type) __attribute__((weak));

static int open_eintr(const char *path, int flags) {
int ret;
do {
ret = open(path, flags);
} while (ret < 0 && errno == EINTR);
return ret;
}

static ssize_t read_eintr(int fd, void *out, size_t len) {
ssize_t ret;
do {
ret = read(fd, out, len);
} while (ret < 0 && errno == EINTR);
return ret;
}

/* read_full reads exactly |len| bytes from |fd| to |out|. On error or end of
* file, it returns zero. */
static int read_full(int fd, void *out, size_t len) {
while (len > 0) {
ssize_t ret = read_eintr(fd, out, len);
if (ret <= 0) {
return 0;
}
out = (uint8_t *)out + ret;
len -= ret;
}
return 1;
}

/* read_file opens |path| and reads until end-of-file. On success, it returns
* one and sets |*out_ptr| and |*out_len| to a newly-allocated buffer with the
* contents. Otherwise, it returns zero. */
static int read_file(char **out_ptr, size_t *out_len, const char *path) {
int fd = open_eintr(path, O_RDONLY);
if (fd < 0) {
return 0;
}

static const size_t kReadSize = 1024;
int ret = 0;
size_t cap = kReadSize, len = 0;
char *buf = OPENSSL_malloc(cap);
if (buf == NULL) {
goto err;
}

for (;;) {
if (cap - len < kReadSize) {
size_t new_cap = cap * 2;
if (new_cap < cap) {
goto err;
}
char *new_buf = OPENSSL_realloc(buf, new_cap);
if (new_buf == NULL) {
goto err;
}
buf = new_buf;
cap = new_cap;
}

ssize_t bytes_read = read_eintr(fd, buf + len, kReadSize);
if (bytes_read < 0) {
goto err;
}
if (bytes_read == 0) {
break;
}
len += bytes_read;
}

*out_ptr = buf;
*out_len = len;
ret = 1;
buf = NULL;

err:
OPENSSL_free(buf);
close(fd);
return ret;
}

/* getauxval_proc behaves like |getauxval| but reads from /proc/self/auxv. */
static unsigned long getauxval_proc(unsigned long type) {
int fd = open_eintr("/proc/self/auxv", O_RDONLY);
if (fd < 0) {
return 0;
}

struct {
unsigned long tag;
unsigned long value;
} entry;

for (;;) {
if (!read_full(fd, &entry, sizeof(entry)) ||
(entry.tag == 0 && entry.value == 0)) {
break;
}
if (entry.tag == type) {
close(fd);
return entry.value;
}
}
close(fd);
return 0;
}

typedef struct {
const char *data;
size_t len;
} STRING_PIECE;

static int STRING_PIECE_equals(const STRING_PIECE *a, const char *b) {
size_t b_len = strlen(b);
return a->len == b_len && memcmp(a->data, b, b_len) == 0;
}

/* STRING_PIECE_split finds the first occurence of |sep| in |in| and, if found,
* sets |*out_left| and |*out_right| to |in| split before and after it. It
* returns one if |sep| was found and zero otherwise. */
static int STRING_PIECE_split(STRING_PIECE *out_left, STRING_PIECE *out_right,
const STRING_PIECE *in, char sep) {
const char *p = memchr(in->data, sep, in->len);
if (p == NULL) {
return 0;
}
/* |out_left| or |out_right| may alias |in|, so make a copy. */
STRING_PIECE in_copy = *in;
out_left->data = in_copy.data;
out_left->len = p - in_copy.data;
out_right->data = in_copy.data + out_left->len + 1;
out_right->len = in_copy.len - out_left->len - 1;
return 1;
}

/* STRING_PIECE_trim removes leading and trailing whitespace from |s|. */
static void STRING_PIECE_trim(STRING_PIECE *s) {
while (s->len != 0 && (s->data[0] == ' ' || s->data[0] == '\t')) {
s->data++;
s->len--;
}
while (s->len != 0 &&
(s->data[s->len - 1] == ' ' || s->data[s->len - 1] == '\t')) {
s->len--;
}
}

/* extract_cpuinfo_field extracts a /proc/cpuinfo field named |field| from
* |in|. If found, it sets |*out| to the value and returns one. Otherwise, it
* returns zero. */
static int extract_cpuinfo_field(STRING_PIECE *out, const STRING_PIECE *in,
const char *field) {
/* Process |in| one line at a time. */
STRING_PIECE remaining = *in, line;
while (STRING_PIECE_split(&line, &remaining, &remaining, '\n')) {
STRING_PIECE key, value;
if (!STRING_PIECE_split(&key, &value, &line, ':')) {
continue;
}
STRING_PIECE_trim(&key);
if (STRING_PIECE_equals(&key, field)) {
STRING_PIECE_trim(&value);
*out = value;
return 1;
}
}

return 0;
}

static int cpuinfo_field_equals(const STRING_PIECE *cpuinfo, const char *field,
const char *value) {
STRING_PIECE extracted;
return extract_cpuinfo_field(&extracted, cpuinfo, field) &&
STRING_PIECE_equals(&extracted, value);
}

/* has_list_item treats |list| as a space-separated list of items and returns
* one if |item| is contained in |list| and zero otherwise. */
static int has_list_item(const STRING_PIECE *list, const char *item) {
STRING_PIECE remaining = *list, feature;
while (STRING_PIECE_split(&feature, &remaining, &remaining, ' ')) {
if (STRING_PIECE_equals(&feature, item)) {
return 1;
}
}
return 0;
}

static unsigned long get_hwcap_cpuinfo(const STRING_PIECE *cpuinfo) {
if (cpuinfo_field_equals(cpuinfo, "CPU architecture", "8")) {
/* This is a 32-bit ARM binary running on a 64-bit kernel. NEON is always
* available on ARMv8. Linux omits required features, so reading the
* "Features" line does not work. (For simplicity, use strict equality. We
* assume everything running on future ARM architectures will have a
* working |getauxval|.) */
return HWCAP_NEON;
}

STRING_PIECE features;
if (extract_cpuinfo_field(&features, cpuinfo, "Features") &&
has_list_item(&features, "neon")) {
return HWCAP_NEON;
}
return 0;
}

static unsigned long get_hwcap2_cpuinfo(const STRING_PIECE *cpuinfo) {
STRING_PIECE features;
if (!extract_cpuinfo_field(&features, cpuinfo, "Features")) {
return 0;
}

unsigned long ret = 0;
if (has_list_item(&features, "aes")) {
ret |= HWCAP2_AES;
}
if (has_list_item(&features, "pmull")) {
ret |= HWCAP2_PMULL;
}
if (has_list_item(&features, "sha1")) {
ret |= HWCAP2_SHA1;
}
if (has_list_item(&features, "sha2")) {
ret |= HWCAP2_SHA2;
}
return ret;
}

/* has_broken_neon returns one if |in| matches a CPU known to have a broken
* NEON unit. See https://crbug.com/341598. */
static int has_broken_neon(const STRING_PIECE *cpuinfo) {
return cpuinfo_field_equals(cpuinfo, "CPU implementer", "0x51") &&
cpuinfo_field_equals(cpuinfo, "CPU architecture", "7") &&
cpuinfo_field_equals(cpuinfo, "CPU variant", "0x1") &&
cpuinfo_field_equals(cpuinfo, "CPU part", "0x04d") &&
cpuinfo_field_equals(cpuinfo, "CPU revision", "0");
}

extern uint32_t GFp_armcap_P;

static int g_has_broken_neon;

void GFp_cpuid_setup(void) {
char *cpuinfo_data;
size_t cpuinfo_len;
if (!read_file(&cpuinfo_data, &cpuinfo_len, "/proc/cpuinfo")) {
return;
}
STRING_PIECE cpuinfo;
cpuinfo.data = cpuinfo_data;
cpuinfo.len = cpuinfo_len;

/* |getauxval| is not available on Android until API level 20. If it is
* unavailable, read from /proc/self/auxv as a fallback. This is unreadable
* on some versions of Android, so further fall back to /proc/cpuinfo.
*
* See
* https://android.googlesource.com/platform/ndk/+/882ac8f3392858991a0e1af33b4b7387ec856bd2
* and b/13679666 (Google-internal) for details. */
unsigned long hwcap = 0;
if (getauxval != NULL) {
hwcap = getauxval(AT_HWCAP);
}
if (hwcap == 0) {
hwcap = getauxval_proc(AT_HWCAP);
}
if (hwcap == 0) {
hwcap = get_hwcap_cpuinfo(&cpuinfo);
}
/*
* getauxval() may or may not be available. In addition, it may not find
* the type requested.
* - If getauxval() is not available, this returns -1.
* - If getauxval() is available but the requested type is not found or another
* error occurs, this returns 0.
* - If getauxval() is available but a different error occurs, this returns -2.
* - If getauxval() is available and the requested type is found, this returns
* 1 and also writes to the result pointer param.
*/
int32_t getauxval_wrapper(unsigned long type, unsigned long *result);

/* Clear NEON support if known broken. */
g_has_broken_neon = has_broken_neon(&cpuinfo);
if (g_has_broken_neon) {
hwcap &= ~HWCAP_NEON;
}

/* Matching OpenSSL, only report other features if NEON is present. */
if (hwcap & HWCAP_NEON) {
GFp_armcap_P |= ARMV7_NEON;
#include <errno.h>

/* Some ARMv8 Android devices don't expose AT_HWCAP2. Fall back to
* /proc/cpuinfo. See https://crbug.com/596156. */
unsigned long hwcap2 = 0;
if (getauxval != NULL) {
hwcap2 = getauxval(AT_HWCAP2);
}
if (hwcap2 == 0) {
hwcap2 = get_hwcap2_cpuinfo(&cpuinfo);
int32_t getauxval_wrapper(unsigned long type, unsigned long *result) {
if (getauxval == NULL) {
return -1;
}

if (hwcap2 & HWCAP2_AES) {
GFp_armcap_P |= ARMV8_AES;
}
if (hwcap2 & HWCAP2_PMULL) {
GFp_armcap_P |= ARMV8_PMULL;
unsigned long auxval = getauxval(type);
if (errno == ENOENT) {
// as of glibc 2.19, errno is ENOENT if the type is not found.
errno = 0;
return 0;
} else if (errno != 0) {
// as of glibc 2.23 the only error is enoent, but more errors
// may be added
errno = 0;
return -2;
}
if (hwcap2 & HWCAP2_SHA1) {
GFp_armcap_P |= ARMV8_SHA1;
}
if (hwcap2 & HWCAP2_SHA2) {
GFp_armcap_P |= ARMV8_SHA256;
}
}

OPENSSL_free(cpuinfo_data);
*result = auxval;
return 1;
}

int GFp_has_broken_NEON(void) { return g_has_broken_neon; }

#endif /* OPENSSL_ARM && !OPENSSL_STATIC_ARMCAP */
#endif
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