linux-imx

/*

 * Copyright 2012-2016 by the PaX Team <pageexec@freemail.hu>

 * Copyright 2016 by Emese Revfy <re.emese@gmail.com>

 * Licensed under the GPL v2

 *

 * Note: the choice of the license means that the compilation process is

 *       NOT 'eligible' as defined by gcc's library exception to the GPL v3,

 *       but for the kernel it doesn't matter since it doesn't link against

 *       any of the gcc libraries

 *

 * This gcc plugin helps generate a little bit of entropy from program state,

 * used throughout the uptime of the kernel. Here is an instrumentation example:

 *

 * before:

 * void __latent_entropy test(int argc, char *argv[])

 * {

 *  if (argc <= 1)

 *      printf("%s: no command arguments :(\n", *argv);

 *  else

 *      printf("%s: %d command arguments!\n", *argv, args - 1);

 * }

 *

 * after:

 * void __latent_entropy test(int argc, char *argv[])

 * {

 *  // latent_entropy_execute() 1.

 *  unsigned long local_entropy;

 *  // init_local_entropy() 1.

 *  void *local_entropy_frameaddr;

 *  // init_local_entropy() 3.

 *  unsigned long tmp_latent_entropy;

 *

 *  // init_local_entropy() 2.

 *  local_entropy_frameaddr = __builtin_frame_address(0);

 *  local_entropy = (unsigned long) local_entropy_frameaddr;

 *

 *  // init_local_entropy() 4.

 *  tmp_latent_entropy = latent_entropy;

 *  // init_local_entropy() 5.

 *  local_entropy ^= tmp_latent_entropy;

 *

 *  // latent_entropy_execute() 3.

 *  if (argc <= 1) {

 *      // perturb_local_entropy()

 *      local_entropy += 4623067384293424948;

 *      printf("%s: no command arguments :(\n", *argv);

 *      // perturb_local_entropy()

 *  } else {

 *      local_entropy ^= 3896280633962944730;

 *      printf("%s: %d command arguments!\n", *argv, args - 1);

 *  }

 *

 *  // latent_entropy_execute() 4.

 *  tmp_latent_entropy = rol(tmp_latent_entropy, local_entropy);

 *  latent_entropy = tmp_latent_entropy;

 * }

 *

 * TODO:

 * - add ipa pass to identify not explicitly marked candidate functions

 * - mix in more program state (function arguments/return values,

 *   loop variables, etc)

 * - more instrumentation control via attribute parameters

 *

 * BUGS:

 * - none known

 *

 * Options:

 * -fplugin-arg-latent_entropy_plugin-disable

 *

 * Attribute: __attribute__((latent_entropy))

 *  The latent_entropy gcc attribute can be only on functions and variables.

 *  If it is on a function then the plugin will instrument it. If the attribute

 *  is on a variable then the plugin will initialize it with a random value.

 *  The variable must be an integer, an integer array type or a structure

 *  with integer fields.

 */

​

#include "gcc-common.h"

​

__visible int plugin_is_GPL_compatible;

​

static GTY(()) tree latent_entropy_decl;

​

static struct plugin_info latent_entropy_plugin_info = {

    .version    = "201606141920vanilla",

    .help       = "disable\tturn off latent entropy instrumentation\n",

};

​

static unsigned HOST_WIDE_INT seed;

/*

 * get_random_seed() (this is a GCC function) generates the seed.

 * This is a simple random generator without any cryptographic security because