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Commit f6112916 authored by Daniel Cashman's avatar Daniel Cashman Committed by dcashman
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Revert "Revert "Set mmap_rnd_bits to maximum value."" 

This reverts commit c8f026fc.

The above revert was meant only for AOSP, not internal master, since the
kernel prebuilts  were not yet available there.  Revert the revert
internally so that internal builds, which have the appropriate kernel
prebuilts, operate properly.

Bug: 27681085
Change-Id: Ide81d43cd22e37979c8266342677db896da1c792
parent f7a0afc3

init/init.cpp

+110 −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 +290,114 @@ 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) {

        ERROR("Cannot open for reading: %s!\n", path.c_str());

        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) {

            ERROR("Cannot open for writing: %s!\n", path.c_str());

            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();

    if (start < min) {

        ERROR("Unable to set minimum required entropy %d in %s!\n",

              min, path.c_str());

        return false;

    }

    return true;

}



/*

 * 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.

 *

 * To support this sysctl, the following upstream commits are needed:

 *

 * d07e22597d1d mm: mmap: add new /proc tunable for mmap_base ASLR

 * e0c25d958f78 arm: mm: support ARCH_MMAP_RND_BITS

 * 8f0d3aa9de57 arm64: mm: support ARCH_MMAP_RND_BITS

 * 9e08f57d684a x86: mm: support ARCH_MMAP_RND_BITS

 * ec9ee4acd97c drivers: char: random: add get_random_long()

 * 5ef11c35ce86 mm: ASLR: use get_random_long()

 */

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



#ifdef __BRILLO__

    // TODO: b/27794137

    ret = 0;

#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 +554,6 @@ 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 +703,7 @@ 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");