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// SPDX-License-Identifier: GPL-2.0-only
/*
* Copyright 2012-2016 by the PaX Team <pageexec@freemail.hu>
* Copyright 2016 by Emese Revfy <re.emese@gmail.com>
*
* 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, argc - 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, 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)
{
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 = >_ggc_mx_tree_node,
.pchw = >_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 *)>_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;
}
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