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Commit 39caeb5b authored by Kees Cook's avatar Kees Cook
Browse files

init: improve mmap ASLR failure reporting 

This should help people track down the reason for entropy setting
failures.

Bug: 27681085
Change-Id: I6bde342ca0215e32c1f851365a1723630c7d4372
parent 8108b80d

init/init.cpp

+18 −4
Original line number Diff line number Diff line
@@ -310,6 +310,7 @@ static bool __attribute__((unused)) set_mmap_rnd_bits_min(int start, int min, bo 
    }

    std::ifstream inf(path, std::fstream::in);

    if (!inf) {

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

        return false;

    }

    while (start >= min) {
@@ -317,6 +318,7 @@ static bool __attribute__((unused)) set_mmap_rnd_bits_min(int start, int min, bo 
        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;
@@ -332,15 +334,27 @@ static bool __attribute__((unused)) set_mmap_rnd_bits_min(int start, int min, bo 
        start--;

    }

    inf.close();

    return (start >= min);

    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.  Apply

 * upstream patch-sets https://lkml.org/lkml/2015/12/21/337 and

 * https://lkml.org/lkml/2016/2/4/831 to enable this.

 * 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)

{