Revert "Revert "Attempt to use arc4random where getauxval(AT_RANDOM) is used.""
This reverts commit 60d052dda600f26fdb6180ac1a2c53e97df5a58a.
Bug: http://b/27729263
Change-Id: I7f32dc9f9a1f21fda3213f10da940821e1bdd63f
diff --git a/libc/bionic/__libc_init_main_thread.cpp b/libc/bionic/__libc_init_main_thread.cpp
index b5a83f4..f3dbfa5 100644
--- a/libc/bionic/__libc_init_main_thread.cpp
+++ b/libc/bionic/__libc_init_main_thread.cpp
@@ -29,6 +29,7 @@
#include "libc_init_common.h"
#include "private/KernelArgumentBlock.h"
+#include "private/bionic_arc4random.h"
#include "private/bionic_auxv.h"
#include "private/bionic_globals.h"
#include "private/bionic_ssp.h"
@@ -41,9 +42,7 @@
uintptr_t __stack_chk_guard = 0;
void __libc_init_global_stack_chk_guard(KernelArgumentBlock& args) {
- // AT_RANDOM is a pointer to 16 bytes of randomness on the stack.
- // Take the first 4/8 for the -fstack-protector implementation.
- __stack_chk_guard = *reinterpret_cast<uintptr_t*>(args.getauxval(AT_RANDOM));
+ __libc_safe_arc4random_buf(&__stack_chk_guard, sizeof(__stack_chk_guard), args);
}
// Setup for the main thread. For dynamic executables, this is called by the
diff --git a/libc/bionic/bionic_arc4random.cpp b/libc/bionic/bionic_arc4random.cpp
new file mode 100644
index 0000000..d20cb68
--- /dev/null
+++ b/libc/bionic/bionic_arc4random.cpp
@@ -0,0 +1,58 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * * Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in
+ * the documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include "private/bionic_arc4random.h"
+
+#include <errno.h>
+#include <stdlib.h>
+#include <sys/auxv.h>
+#include <syscall.h>
+#include <unistd.h>
+
+#include "private/KernelArgumentBlock.h"
+#include "private/libc_logging.h"
+
+void __libc_safe_arc4random_buf(void* buf, size_t n, KernelArgumentBlock& args) {
+ static bool have_getrandom = syscall(SYS_getrandom, nullptr, 0, 0) == -1 && errno != ENOSYS;
+ static bool have_urandom = access("/dev/urandom", R_OK) == 0;
+ static size_t at_random_bytes_consumed = 0;
+
+ if (have_getrandom || have_urandom) {
+ arc4random_buf(buf, n);
+ return;
+ }
+
+ if (at_random_bytes_consumed + n > 16) {
+ __libc_fatal("ran out of AT_RANDOM bytes, have %zu, requested %zu",
+ 16 - at_random_bytes_consumed, n);
+ }
+
+ memcpy(buf, reinterpret_cast<char*>(args.getauxval(AT_RANDOM)) + at_random_bytes_consumed, n);
+ at_random_bytes_consumed += n;
+ return;
+}
diff --git a/libc/bionic/setjmp_cookie.cpp b/libc/bionic/setjmp_cookie.cpp
index 3be675a..4fa68c2 100644
--- a/libc/bionic/setjmp_cookie.cpp
+++ b/libc/bionic/setjmp_cookie.cpp
@@ -34,14 +34,14 @@
#include <sys/auxv.h>
#include <sys/cdefs.h>
+#include "private/bionic_arc4random.h"
#include "private/bionic_globals.h"
#include "private/libc_logging.h"
#include "private/KernelArgumentBlock.h"
-void __libc_init_setjmp_cookie(libc_globals* globals,
- KernelArgumentBlock& args) {
- char* random_data = reinterpret_cast<char*>(args.getauxval(AT_RANDOM));
- long value = *reinterpret_cast<long*>(random_data + 8);
+void __libc_init_setjmp_cookie(libc_globals* globals, KernelArgumentBlock& args) {
+ long value;
+ __libc_safe_arc4random_buf(&value, sizeof(value), args);
// Mask off the last bit to store the signal flag.
globals->setjmp_cookie = value & ~1;