linux/scripts/gcc-plugins/latent_entropy_plugin.c at master · penLab101/linux · GitHub

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* 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 = 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)

{

tree type;

vec<constructor_elt, va_gc> *vals;

switch (TREE_CODE(*node)) {

default:

*no_add_attrs = true;

error("%qE attribute only applies to functions and variables",

name);

break;

case VAR_DECL:

if (DECL_INITIAL(*node)) {

*no_add_attrs = true;

error("variable %qD with %qE attribute must not be initialized",

*node, name);

break;

}

if (!TREE_STATIC(*node)) {

*no_add_attrs = true;

error("variable %qD with %qE attribute must not be local",

*node, name);

break;

}

type = TREE_TYPE(*node);

switch (TREE_CODE(type)) {

default:

*no_add_attrs = true;

error("variable %qD with %qE attribute must be an integer or a fixed length integer array type or a fixed sized structure with integer fields",

*node, name);

break;

case RECORD_TYPE: {

tree fld, lst = TYPE_FIELDS(type);

unsigned int nelt = 0;

for (fld = lst; fld; nelt++, fld = TREE_CHAIN(fld)) {

tree fieldtype;

fieldtype = TREE_TYPE(fld);

if (TREE_CODE(fieldtype) == INTEGER_TYPE)

continue;

*no_add_attrs = true;

error("structure variable %qD with %qE attribute has a non-integer field %qE",

*node, name, fld);

break;

}

if (fld)

break;

vec_alloc(vals, nelt);

for (fld = lst; fld; fld = TREE_CHAIN(fld)) {

tree random_const, fld_t = TREE_TYPE(fld);

random_const = tree_get_random_const(fld_t);

CONSTRUCTOR_APPEND_ELT(vals, fld, random_const);

}

/* Initialize the fields with random constants */

DECL_INITIAL(*node) = build_constructor(type, vals);

break;

}

/* Initialize the variable with a random constant */

case INTEGER_TYPE:

DECL_INITIAL(*node) = tree_get_random_const(type);

break;

case ARRAY_TYPE: {

tree elt_type, array_size, elt_size;

unsigned int i, nelt;

HOST_WIDE_INT array_size_int, elt_size_int;

elt_type = TREE_TYPE(type);

elt_size = TYPE_SIZE_UNIT(TREE_TYPE(type));

array_size = TYPE_SIZE_UNIT(type);

if (TREE_CODE(elt_type) != INTEGER_TYPE || !array_size

|| TREE_CODE(array_size) != INTEGER_CST) {

*no_add_attrs = true;

error("array variable %qD with %qE attribute must be a fixed length integer array type",

*node, name);

break;

}

array_size_int = TREE_INT_CST_LOW(array_size);

elt_size_int = TREE_INT_CST_LOW(elt_size);

nelt = array_size_int / elt_size_int;

vec_alloc(vals, nelt);

for (i = 0; i < nelt; i++) {

tree cst = size_int(i);

tree rand_cst = tree_get_random_const(elt_type);

CONSTRUCTOR_APPEND_ELT(vals, cst, rand_cst);

}

* Initialize the elements of the array with random

* constants

DECL_INITIAL(*node) = build_constructor(type, vals);

break;

}

break;

case FUNCTION_DECL:

break;

}

return NULL_TREE;

}

static struct attribute_spec latent_entropy_attr = { };

static void register_attributes(void *event_data __unused, void *data __unused)

{

latent_entropy_attr.name = "latent_entropy";

latent_entropy_attr.decl_required = true;

latent_entropy_attr.handler = handle_latent_entropy_attribute;

register_attribute(&latent_entropy_attr);

}

static bool latent_entropy_gate(void)

{

tree list;

/* don't bother with noreturn functions for now */

if (TREE_THIS_VOLATILE(current_function_decl))

return false;

/* gcc-4.5 doesn't discover some trivial noreturn functions */

if (EDGE_COUNT(EXIT_BLOCK_PTR_FOR_FN(cfun)->preds) == 0)

return false;

list = DECL_ATTRIBUTES(current_function_decl);

return lookup_attribute("latent_entropy", list) != NULL_TREE;

}

static tree create_var(tree type, const char *name)

{

tree var;

var = create_tmp_var(type, name);

add_referenced_var(var);

mark_sym_for_renaming(var);

return var;

}

* Set up the next operation and its constant operand to use in the latent

* entropy PRNG. When RHS is specified, the request is for perturbing the

* local latent entropy variable, otherwise it is for perturbing the global

* latent entropy variable where the two operands are already given by the

* local and global latent entropy variables themselves.

* The operation is one of add/xor/rol when instrumenting the local entropy

* variable and one of add/xor when perturbing the global entropy variable.

* Rotation is not used for the latter case because it would transmit less

* entropy to the global variable than the other two operations.

static enum tree_code get_op(tree *rhs)

{

static enum tree_code op;

unsigned HOST_WIDE_INT random_const;

random_const = get_random_const();

switch (op) {

case BIT_XOR_EXPR:

op = PLUS_EXPR;

break;

case PLUS_EXPR:

if (rhs) {

op = LROTATE_EXPR;

* This code limits the value of random_const to

* the size of a long for the rotation

random_const %= TYPE_PRECISION(long_unsigned_type_node);

break;

}

case LROTATE_EXPR:

default:

op = BIT_XOR_EXPR;

break;

}

if (rhs)

*rhs = build_int_cstu(long_unsigned_type_node, random_const);

return op;

}

static gimple create_assign(enum tree_code code, tree lhs, tree op1,

tree op2)

{

return gimple_build_assign_with_ops(code, lhs, op1, op2);

}

static void perturb_local_entropy(basic_block bb, tree local_entropy)

{

gimple_stmt_iterator gsi;

gimple assign;

tree rhs;

enum tree_code op;

op = get_op(&rhs);

assign = create_assign(op, local_entropy, local_entropy, rhs);

gsi = gsi_after_labels(bb);

gsi_insert_before(&gsi, assign, GSI_NEW_STMT);

update_stmt(assign);

}

static void __perturb_latent_entropy(gimple_stmt_iterator *gsi,

tree local_entropy)

{

gimple assign;

tree temp;

enum tree_code op;

/* 1. create temporary copy of latent_entropy */

temp = create_var(long_unsigned_type_node, "temp_latent_entropy");

/* 2. read... */

add_referenced_var(latent_entropy_decl);

mark_sym_for_renaming(latent_entropy_decl);

assign = gimple_build_assign(temp, latent_entropy_decl);

gsi_insert_before(gsi, assign, GSI_NEW_STMT);

update_stmt(assign);

/* 3. ...modify... */

op = get_op(NULL);

assign = create_assign(op, temp, temp, local_entropy);

gsi_insert_after(gsi, assign, GSI_NEW_STMT);

update_stmt(assign);

/* 4. ...write latent_entropy */

assign = gimple_build_assign(latent_entropy_decl, temp);

gsi_insert_after(gsi, assign, GSI_NEW_STMT);

update_stmt(assign);

}

static bool handle_tail_calls(basic_block bb, tree local_entropy)

{

gimple_stmt_iterator gsi;

for (gsi = gsi_start_bb(bb); !gsi_end_p(gsi); gsi_next(&gsi)) {

gcall *call;

gimple stmt = gsi_stmt(gsi);

if (!is_gimple_call(stmt))

continue;

call = as_a_gcall(stmt);

if (!gimple_call_tail_p(call))

continue;

__perturb_latent_entropy(&gsi, local_entropy);

return true;

}

return false;

}

static void perturb_latent_entropy(tree local_entropy)

{

edge_iterator ei;

edge e, last_bb_e;

basic_block last_bb;

gcc_assert(single_pred_p(EXIT_BLOCK_PTR_FOR_FN(cfun)));

last_bb_e = single_pred_edge(EXIT_BLOCK_PTR_FOR_FN(cfun));

FOR_EACH_EDGE(e, ei, last_bb_e->src->preds) {

if (ENTRY_BLOCK_PTR_FOR_FN(cfun) == e->src)

continue;

if (EXIT_BLOCK_PTR_FOR_FN(cfun) == e->src)

continue;

handle_tail_calls(e->src, local_entropy);

}

last_bb = single_pred(EXIT_BLOCK_PTR_FOR_FN(cfun));

if (!handle_tail_calls(last_bb, local_entropy)) {

gimple_stmt_iterator gsi = gsi_last_bb(last_bb);

__perturb_latent_entropy(&gsi, local_entropy);

}

static void init_local_entropy(basic_block bb, tree local_entropy)

{

gimple assign, call;

tree frame_addr, rand_const, tmp, fndecl, udi_frame_addr;

enum tree_code op;

unsigned HOST_WIDE_INT rand_cst;

gimple_stmt_iterator gsi = gsi_after_labels(bb);

/* 1. create local_entropy_frameaddr */

frame_addr = create_var(ptr_type_node, "local_entropy_frameaddr");

/* 2. local_entropy_frameaddr = __builtin_frame_address() */

fndecl = builtin_decl_implicit(BUILT_IN_FRAME_ADDRESS);

call = gimple_build_call(fndecl, 1, integer_zero_node);

gimple_call_set_lhs(call, frame_addr);

gsi_insert_before(&gsi, call, GSI_NEW_STMT);

update_stmt(call);

udi_frame_addr = fold_convert(long_unsigned_type_node, frame_addr);

assign = gimple_build_assign(local_entropy, udi_frame_addr);

gsi_insert_after(&gsi, assign, GSI_NEW_STMT);

update_stmt(assign);

/* 3. create temporary copy of latent_entropy */

tmp = create_var(long_unsigned_type_node, "temp_latent_entropy");

/* 4. read the global entropy variable into local entropy */

add_referenced_var(latent_entropy_decl);

mark_sym_for_renaming(latent_entropy_decl);

assign = gimple_build_assign(tmp, latent_entropy_decl);

gsi_insert_after(&gsi, assign, GSI_NEW_STMT);

update_stmt(assign);

/* 5. mix local_entropy_frameaddr into local entropy */

assign = create_assign(BIT_XOR_EXPR, local_entropy, local_entropy, tmp);

gsi_insert_after(&gsi, assign, GSI_NEW_STMT);

update_stmt(assign);

rand_cst = get_random_const();

rand_const = build_int_cstu(long_unsigned_type_node, rand_cst);

op = get_op(NULL);

assign = create_assign(op, local_entropy, local_entropy, rand_const);

gsi_insert_after(&gsi, assign, GSI_NEW_STMT);

update_stmt(assign);

}

static bool create_latent_entropy_decl(void)

{

varpool_node_ptr node;

if (latent_entropy_decl != NULL_TREE)

return true;

FOR_EACH_VARIABLE(node) {

tree name, var = NODE_DECL(node);

if (DECL_NAME_LENGTH(var) < sizeof("latent_entropy") - 1)

continue;

name = DECL_NAME(var);

if (strcmp(IDENTIFIER_POINTER(name), "latent_entropy"))

continue;

latent_entropy_decl = var;

break;

}

return latent_entropy_decl != NULL_TREE;

}

static unsigned int latent_entropy_execute(void)

{

basic_block bb;

tree local_entropy;

if (!create_latent_entropy_decl())

return 0;

/* prepare for step 2 below */

gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));

bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));

if (!single_pred_p(bb)) {

split_edge(single_succ_edge(ENTRY_BLOCK_PTR_FOR_FN(cfun)));

gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));

bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));

}

/* 1. create the local entropy variable */

local_entropy = create_var(long_unsigned_type_node, "local_entropy");

/* 2. initialize the local entropy variable */

init_local_entropy(bb, local_entropy);

bb = bb->next_bb;

* 3. instrument each BB with an operation on the

* local entropy variable

while (bb != EXIT_BLOCK_PTR_FOR_FN(cfun)) {

perturb_local_entropy(bb, local_entropy);

bb = bb->next_bb;

}

/* 4. mix local entropy into the global entropy variable */

perturb_latent_entropy(local_entropy);

return 0;

}

static void latent_entropy_start_unit(void *gcc_data __unused,

void *user_data __unused)

{

tree type, id;

int quals;

if (in_lto_p)

return;

/* extern volatile unsigned long latent_entropy */

quals = TYPE_QUALS(long_unsigned_type_node) | TYPE_QUAL_VOLATILE;

type = build_qualified_type(long_unsigned_type_node, quals);

id = get_identifier("latent_entropy");

latent_entropy_decl = build_decl(UNKNOWN_LOCATION, VAR_DECL, id, type);

TREE_STATIC(latent_entropy_decl) = 1;

TREE_PUBLIC(latent_entropy_decl) = 1;

TREE_USED(latent_entropy_decl) = 1;

DECL_PRESERVE_P(latent_entropy_decl) = 1;

TREE_THIS_VOLATILE(latent_entropy_decl) = 1;

DECL_EXTERNAL(latent_entropy_decl) = 1;

DECL_ARTIFICIAL(latent_entropy_decl) = 1;

lang_hooks.decls.pushdecl(latent_entropy_decl);

}

#define PASS_NAME latent_entropy

#define PROPERTIES_REQUIRED PROP_gimple_leh | PROP_cfg

#define TODO_FLAGS_FINISH TODO_verify_ssa | TODO_verify_stmts | TODO_dump_func \

| TODO_update_ssa

#include "gcc-generate-gimple-pass.h"

__visible int plugin_init(struct plugin_name_args *plugin_info,

struct plugin_gcc_version *version)

{

bool enabled = true;

const char * const plugin_name = plugin_info->base_name;

const int argc = plugin_info->argc;

const struct plugin_argument * const argv = plugin_info->argv;

int i;

* Call get_random_seed() with noinit=true, so that this returns

* 0 in the case where no seed has been passed via -frandom-seed.

deterministic_seed = get_random_seed(true);

static const struct ggc_root_tab gt_ggc_r_gt_latent_entropy[] = {

{

.base = &latent_entropy_decl,

.nelt = 1,

.stride = sizeof(latent_entropy_decl),

.cb = &gt_ggc_mx_tree_node,

.pchw = &gt_pch_nx_tree_node

LAST_GGC_ROOT_TAB

};

PASS_INFO(latent_entropy, "optimized", 1, PASS_POS_INSERT_BEFORE);

if (!plugin_default_version_check(version, &gcc_version)) {

error(G_("incompatible gcc/plugin versions"));

return 1;

}

for (i = 0; i < argc; ++i) {

if (!(strcmp(argv[i].key, "disable"))) {

enabled = false;

continue;

}

error(G_("unknown option '-fplugin-arg-%s-%s'"), plugin_name, argv[i].key);

}

register_callback(plugin_name, PLUGIN_INFO, NULL,

&latent_entropy_plugin_info);

if (enabled) {

register_callback(plugin_name, PLUGIN_START_UNIT,

&latent_entropy_start_unit, NULL);

register_callback(plugin_name, PLUGIN_REGISTER_GGC_ROOTS,

NULL, (void *)&gt_ggc_r_gt_latent_entropy);

register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL,

&latent_entropy_pass_info);

}

register_callback(plugin_name, PLUGIN_ATTRIBUTES, register_attributes,

NULL);

return 0;

}

linux/scripts/gcc-plugins/latent_entropy_plugin.c at master · penLab101/linux · GitHub

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