scripts/gcc-plugins/latent_entropy_plugin.c

Source file repositories/reference/linux-study-clean/scripts/gcc-plugins/latent_entropy_plugin.c

File Facts

System
Linux kernel
Corpus path
scripts/gcc-plugins/latent_entropy_plugin.c
Extension
.c
Size
17100 bytes
Lines
627
Domain
Support Tooling And Documentation
Bucket
scripts
Inferred role
Support Tooling And Documentation: implementation source
Status
source implementation candidate

Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

Dependency Surface

Detected Declarations

Annotated Snippet

*	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, argc - 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	= PLUGIN_VERSION,
	.help		= "disable\tturn off latent entropy instrumentation\n",
};

static unsigned HOST_WIDE_INT deterministic_seed;
static unsigned HOST_WIDE_INT rnd_buf[32];
static size_t rnd_idx = ARRAY_SIZE(rnd_buf);
static int urandom_fd = -1;

static unsigned HOST_WIDE_INT get_random_const(void)
{
	if (deterministic_seed) {
		unsigned HOST_WIDE_INT w = deterministic_seed;
		w ^= w << 13;
		w ^= w >> 7;
		w ^= w << 17;
		deterministic_seed = w;
		return deterministic_seed;
	}

	if (urandom_fd < 0) {
		urandom_fd = open("/dev/urandom", O_RDONLY);
		gcc_assert(urandom_fd >= 0);
	}
	if (rnd_idx >= ARRAY_SIZE(rnd_buf)) {
		gcc_assert(read(urandom_fd, rnd_buf, sizeof(rnd_buf)) == sizeof(rnd_buf));
		rnd_idx = 0;
	}
	return rnd_buf[rnd_idx++];
}

static tree tree_get_random_const(tree type)
{
	unsigned long long mask;

	mask = 1ULL << (TREE_INT_CST_LOW(TYPE_SIZE(type)) - 1);
	mask = 2 * (mask - 1) + 1;

	if (TYPE_UNSIGNED(type))
		return build_int_cstu(type, mask & get_random_const());
	return build_int_cst(type, mask & get_random_const());
}

static tree handle_latent_entropy_attribute(tree *node, tree name,
						tree args __unused,
						int flags __unused,
						bool *no_add_attrs)
{

Annotation

Implementation Notes