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Commit c819e78e authored by dcashman's avatar dcashman
Browse files

Set mmap_rnd_bits to maximum value. 

Also make sure it is above a minimum threshold, else abort.

(cherry-pick of internal commit: 5d36813d)

Bug: 27681085
Change-Id: Ia1d9583254fd64828092533298a99ec64b8233f7
parent 80b1b188

init/init.cpp

+91 −6
Original line number Diff line number Diff line
@@ -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 @@ ret: 
    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 @@ static int audit_callback(void *data, security_class_t /*cls*/, char *buf, size_ 
    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 @@ int main(int argc, char** argv) { 
    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");