Set mmap_rnd_bits to maximum value.
Also make sure it is above a minimum threshold, else abort.
(cherry-pick of internal commit: 5d36813dc8d3be3f62856cf5147b828a7a8594a7)
Bug: 27681085
Change-Id: Ia1d9583254fd64828092533298a99ec64b8233f7
diff --git a/init/init.cpp b/init/init.cpp
index 9b7d108..b1e3a9d 100644
--- a/init/init.cpp
+++ b/init/init.cpp
@@ -18,6 +18,7 @@
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
+#include <fstream>
#include <libgen.h>
#include <paths.h>
#include <signal.h>
@@ -289,6 +290,95 @@
return result;
}
+static void security_failure() {
+ ERROR("Security failure; rebooting into recovery mode...\n");
+ android_reboot(ANDROID_RB_RESTART2, 0, "recovery");
+ while (true) { pause(); } // never reached
+}
+
+#define MMAP_RND_PATH "/proc/sys/vm/mmap_rnd_bits"
+#define MMAP_RND_COMPAT_PATH "/proc/sys/vm/mmap_rnd_compat_bits"
+
+/* __attribute__((unused)) due to lack of mips support: see mips block
+ * in set_mmap_rnd_bits_action */
+static bool __attribute__((unused)) set_mmap_rnd_bits_min(int start, int min, bool compat) {
+ std::string path;
+ if (compat) {
+ path = MMAP_RND_COMPAT_PATH;
+ } else {
+ path = MMAP_RND_PATH;
+ }
+ std::ifstream inf(path, std::fstream::in);
+ if (!inf) {
+ return false;
+ }
+ while (start >= min) {
+ // try to write out new value
+ std::string str_val = std::to_string(start);
+ std::ofstream of(path, std::fstream::out);
+ if (!of) {
+ return false;
+ }
+ of << str_val << std::endl;
+ of.close();
+
+ // check to make sure it was recorded
+ inf.seekg(0);
+ std::string str_rec;
+ inf >> str_rec;
+ if (str_val.compare(str_rec) == 0) {
+ break;
+ }
+ start--;
+ }
+ inf.close();
+ return (start >= min);
+}
+
+/*
+ * Set /proc/sys/vm/mmap_rnd_bits and potentially
+ * /proc/sys/vm/mmap_rnd_compat_bits to the maximum supported values.
+ * Returns -1 if unable to set these to an acceptable value. Apply
+ * upstream patch-sets https://lkml.org/lkml/2015/12/21/337 and
+ * https://lkml.org/lkml/2016/2/4/831 to enable this.
+ */
+static int set_mmap_rnd_bits_action(const std::vector<std::string>& args)
+{
+ int ret = -1;
+
+ /* values are arch-dependent */
+#if defined(__aarch64__)
+ /* arm64 supports 18 - 33 bits depending on pagesize and VA_SIZE */
+ if (set_mmap_rnd_bits_min(33, 24, false)
+ && set_mmap_rnd_bits_min(16, 16, true)) {
+ ret = 0;
+ }
+#elif defined(__x86__64__)
+ /* x86_64 supports 28 - 32 bits */
+ if (set_mmap_rnd_bits_min(32, 32, false)
+ && set_mmap_rnd_bits_min(16, 16, true)) {
+ ret = 0;
+ }
+#elif defined(__arm__) || defined(__i386__)
+ /* check to see if we're running on 64-bit kernel */
+ bool h64 = !access(MMAP_RND_COMPAT_PATH, F_OK);
+ /* supported 32-bit architecture must have 16 bits set */
+ if (set_mmap_rnd_bits_min(16, 16, h64)) {
+ ret = 0;
+ }
+#elif defined(__mips__) || defined(__mips64__)
+ // TODO: add mips support b/27788820
+ ret = 0;
+#else
+ ERROR("Unknown architecture\n");
+#endif
+ if (ret == -1) {
+ ERROR("Unable to set adequate mmap entropy value!\n");
+ security_failure();
+ }
+ return ret;
+}
+
static int keychord_init_action(const std::vector<std::string>& args)
{
keychord_init();
@@ -445,12 +535,6 @@
return 0;
}
-static void security_failure() {
- ERROR("Security failure; rebooting into recovery mode...\n");
- android_reboot(ANDROID_RB_RESTART2, 0, "recovery");
- while (true) { pause(); } // never reached
-}
-
static void selinux_initialize(bool in_kernel_domain) {
Timer t;
@@ -600,6 +684,7 @@
am.QueueBuiltinAction(wait_for_coldboot_done_action, "wait_for_coldboot_done");
// ... so that we can start queuing up actions that require stuff from /dev.
am.QueueBuiltinAction(mix_hwrng_into_linux_rng_action, "mix_hwrng_into_linux_rng");
+ am.QueueBuiltinAction(set_mmap_rnd_bits_action, "set_mmap_rnd_bits");
am.QueueBuiltinAction(keychord_init_action, "keychord_init");
am.QueueBuiltinAction(console_init_action, "console_init");