1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Copyright 2012-2016 by the PaX Team <pageexec@freemail.hu>
4 * Copyright 2016 by Emese Revfy <re.emese@gmail.com>
5 *
6 * Note: the choice of the license means that the compilation process is
7 * NOT 'eligible' as defined by gcc's library exception to the GPL v3,
8 * but for the kernel it doesn't matter since it doesn't link against
9 * any of the gcc libraries
10 *
11 * This gcc plugin helps generate a little bit of entropy from program state,
12 * used throughout the uptime of the kernel. Here is an instrumentation example:
13 *
14 * before:
15 * void __latent_entropy test(int argc, char *argv[])
16 * {
17 * if (argc <= 1)
18 * printf("%s: no command arguments :(\n", *argv);
19 * else
20 * printf("%s: %d command arguments!\n", *argv, argc - 1);
21 * }
22 *
23 * after:
24 * void __latent_entropy test(int argc, char *argv[])
25 * {
26 * // latent_entropy_execute() 1.
27 * unsigned long local_entropy;
28 * // init_local_entropy() 1.
29 * void *local_entropy_frameaddr;
30 * // init_local_entropy() 3.
31 * unsigned long tmp_latent_entropy;
32 *
33 * // init_local_entropy() 2.
34 * local_entropy_frameaddr = __builtin_frame_address(0);
35 * local_entropy = (unsigned long) local_entropy_frameaddr;
36 *
37 * // init_local_entropy() 4.
38 * tmp_latent_entropy = latent_entropy;
39 * // init_local_entropy() 5.
40 * local_entropy ^= tmp_latent_entropy;
41 *
42 * // latent_entropy_execute() 3.
43 * if (argc <= 1) {
44 * // perturb_local_entropy()
45 * local_entropy += 4623067384293424948;
46 * printf("%s: no command arguments :(\n", *argv);
47 * // perturb_local_entropy()
48 * } else {
49 * local_entropy ^= 3896280633962944730;
50 * printf("%s: %d command arguments!\n", *argv, argc - 1);
51 * }
52 *
53 * // latent_entropy_execute() 4.
54 * tmp_latent_entropy = rol(tmp_latent_entropy, local_entropy);
55 * latent_entropy = tmp_latent_entropy;
56 * }
57 *
58 * TODO:
59 * - add ipa pass to identify not explicitly marked candidate functions
60 * - mix in more program state (function arguments/return values,
61 * loop variables, etc)
62 * - more instrumentation control via attribute parameters
63 *
64 * BUGS:
65 * - none known
66 *
67 * Options:
68 * -fplugin-arg-latent_entropy_plugin-disable
69 *
70 * Attribute: __attribute__((latent_entropy))
71 * The latent_entropy gcc attribute can be only on functions and variables.
72 * If it is on a function then the plugin will instrument it. If the attribute
73 * is on a variable then the plugin will initialize it with a random value.
74 * The variable must be an integer, an integer array type or a structure
75 * with integer fields.
76 */
77
78 #include "gcc-common.h"
79
80 __visible int plugin_is_GPL_compatible;
81
82 static GTY(()) tree latent_entropy_decl;
83
84 static struct plugin_info latent_entropy_plugin_info = {
85 .version = PLUGIN_VERSION,
86 .help = "disable\tturn off latent entropy instrumentation\n",
87 };
88
89 static unsigned HOST_WIDE_INT deterministic_seed;
90 static unsigned HOST_WIDE_INT rnd_buf[32];
91 static size_t rnd_idx = ARRAY_SIZE(rnd_buf);
92 static int urandom_fd = -1;
93
94 static unsigned HOST_WIDE_INT get_random_const(void)
95 {
96 if (deterministic_seed) {
97 unsigned HOST_WIDE_INT w = deterministic_seed;
98 w ^= w << 13;
99 w ^= w >> 7;
100 w ^= w << 17;
101 deterministic_seed = w;
102 return deterministic_seed;
103 }
104
105 if (urandom_fd < 0) {
106 urandom_fd = open("/dev/urandom", O_RDONLY);
107 gcc_assert(urandom_fd >= 0);
108 }
109 if (rnd_idx >= ARRAY_SIZE(rnd_buf)) {
110 gcc_assert(read(urandom_fd, rnd_buf, sizeof(rnd_buf)) == sizeof(rnd_buf));
111 rnd_idx = 0;
112 }
113 return rnd_buf[rnd_idx++];
114 }
115
116 static tree tree_get_random_const(tree type)
117 {
118 unsigned long long mask;
119
120 mask = 1ULL << (TREE_INT_CST_LOW(TYPE_SIZE(type)) - 1);
121 mask = 2 * (mask - 1) + 1;
122
123 if (TYPE_UNSIGNED(type))
124 return build_int_cstu(type, mask & get_random_const());
125 return build_int_cst(type, mask & get_random_const());
126 }
127
128 static tree handle_latent_entropy_attribute(tree *node, tree name,
129 tree args __unused,
130 int flags __unused,
131 bool *no_add_attrs)
132 {
133 tree type;
134 vec<constructor_elt, va_gc> *vals;
135
136 switch (TREE_CODE(*node)) {
137 default:
138 *no_add_attrs = true;
139 error("%qE attribute only applies to functions and variables",
140 name);
141 break;
142
143 case VAR_DECL:
144 if (DECL_INITIAL(*node)) {
145 *no_add_attrs = true;
146 error("variable %qD with %qE attribute must not be initialized",
147 *node, name);
148 break;
149 }
150
151 if (!TREE_STATIC(*node)) {
152 *no_add_attrs = true;
153 error("variable %qD with %qE attribute must not be local",
154 *node, name);
155 break;
156 }
157
158 type = TREE_TYPE(*node);
159 switch (TREE_CODE(type)) {
160 default:
161 *no_add_attrs = true;
162 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",
163 *node, name);
164 break;
165
166 case RECORD_TYPE: {
167 tree fld, lst = TYPE_FIELDS(type);
168 unsigned int nelt = 0;
169
170 for (fld = lst; fld; nelt++, fld = TREE_CHAIN(fld)) {
171 tree fieldtype;
172
173 fieldtype = TREE_TYPE(fld);
174 if (TREE_CODE(fieldtype) == INTEGER_TYPE)
175 continue;
176
177 *no_add_attrs = true;
178 error("structure variable %qD with %qE attribute has a non-integer field %qE",
179 *node, name, fld);
180 break;
181 }
182
183 if (fld)
184 break;
185
186 vec_alloc(vals, nelt);
187
188 for (fld = lst; fld; fld = TREE_CHAIN(fld)) {
189 tree random_const, fld_t = TREE_TYPE(fld);
190
191 random_const = tree_get_random_const(fld_t);
192 CONSTRUCTOR_APPEND_ELT(vals, fld, random_const);
193 }
194
195 /* Initialize the fields with random constants */
196 DECL_INITIAL(*node) = build_constructor(type, vals);
197 break;
198 }
199
200 /* Initialize the variable with a random constant */
201 case INTEGER_TYPE:
202 DECL_INITIAL(*node) = tree_get_random_const(type);
203 break;
204
205 case ARRAY_TYPE: {
206 tree elt_type, array_size, elt_size;
207 unsigned int i, nelt;
208 HOST_WIDE_INT array_size_int, elt_size_int;
209
210 elt_type = TREE_TYPE(type);
211 elt_size = TYPE_SIZE_UNIT(TREE_TYPE(type));
212 array_size = TYPE_SIZE_UNIT(type);
213
214 if (TREE_CODE(elt_type) != INTEGER_TYPE || !array_size
215 || TREE_CODE(array_size) != INTEGER_CST) {
216 *no_add_attrs = true;
217 error("array variable %qD with %qE attribute must be a fixed length integer array type",
218 *node, name);
219 break;
220 }
221
222 array_size_int = TREE_INT_CST_LOW(array_size);
223 elt_size_int = TREE_INT_CST_LOW(elt_size);
224 nelt = array_size_int / elt_size_int;
225
226 vec_alloc(vals, nelt);
227
228 for (i = 0; i < nelt; i++) {
229 tree cst = size_int(i);
230 tree rand_cst = tree_get_random_const(elt_type);
231
232 CONSTRUCTOR_APPEND_ELT(vals, cst, rand_cst);
233 }
234
235 /*
236 * Initialize the elements of the array with random
237 * constants
238 */
239 DECL_INITIAL(*node) = build_constructor(type, vals);
240 break;
241 }
242 }
243 break;
244
245 case FUNCTION_DECL:
246 break;
247 }
248
249 return NULL_TREE;
250 }
251
252 static struct attribute_spec latent_entropy_attr = { };
253
254 static void register_attributes(void *event_data __unused, void *data __unused)
255 {
256 latent_entropy_attr.name = "latent_entropy";
257 latent_entropy_attr.decl_required = true;
258 latent_entropy_attr.handler = handle_latent_entropy_attribute;
259
260 register_attribute(&latent_entropy_attr);
261 }
262
263 static bool latent_entropy_gate(void)
264 {
265 tree list;
266
267 /* don't bother with noreturn functions for now */
268 if (TREE_THIS_VOLATILE(current_function_decl))
269 return false;
270
271 /* gcc-4.5 doesn't discover some trivial noreturn functions */
272 if (EDGE_COUNT(EXIT_BLOCK_PTR_FOR_FN(cfun)->preds) == 0)
273 return false;
274
275 list = DECL_ATTRIBUTES(current_function_decl);
276 return lookup_attribute("latent_entropy", list) != NULL_TREE;
277 }
278
279 static tree create_var(tree type, const char *name)
280 {
281 tree var;
282
283 var = create_tmp_var(type, name);
284 add_referenced_var(var);
285 mark_sym_for_renaming(var);
286 return var;
287 }
288
289 /*
290 * Set up the next operation and its constant operand to use in the latent
291 * entropy PRNG. When RHS is specified, the request is for perturbing the
292 * local latent entropy variable, otherwise it is for perturbing the global
293 * latent entropy variable where the two operands are already given by the
294 * local and global latent entropy variables themselves.
295 *
296 * The operation is one of add/xor/rol when instrumenting the local entropy
297 * variable and one of add/xor when perturbing the global entropy variable.
298 * Rotation is not used for the latter case because it would transmit less
299 * entropy to the global variable than the other two operations.
300 */
301 static enum tree_code get_op(tree *rhs)
302 {
303 static enum tree_code op;
304 unsigned HOST_WIDE_INT random_const;
305
306 random_const = get_random_const();
307
308 switch (op) {
309 case BIT_XOR_EXPR:
310 op = PLUS_EXPR;
311 break;
312
313 case PLUS_EXPR:
314 if (rhs) {
315 op = LROTATE_EXPR;
316 /*
317 * This code limits the value of random_const to
318 * the size of a long for the rotation
319 */
320 random_const %= TYPE_PRECISION(long_unsigned_type_node);
321 break;
322 }
323
324 case LROTATE_EXPR:
325 default:
326 op = BIT_XOR_EXPR;
327 break;
328 }
329 if (rhs)
330 *rhs = build_int_cstu(long_unsigned_type_node, random_const);
331 return op;
332 }
333
334 static gimple create_assign(enum tree_code code, tree lhs, tree op1,
335 tree op2)
336 {
337 return gimple_build_assign_with_ops(code, lhs, op1, op2);
338 }
339
340 static void perturb_local_entropy(basic_block bb, tree local_entropy)
341 {
342 gimple_stmt_iterator gsi;
343 gimple assign;
344 tree rhs;
345 enum tree_code op;
346
347 op = get_op(&rhs);
348 assign = create_assign(op, local_entropy, local_entropy, rhs);
349 gsi = gsi_after_labels(bb);
350 gsi_insert_before(&gsi, assign, GSI_NEW_STMT);
351 update_stmt(assign);
352 }
353
354 static void __perturb_latent_entropy(gimple_stmt_iterator *gsi,
355 tree local_entropy)
356 {
357 gimple assign;
358 tree temp;
359 enum tree_code op;
360
361 /* 1. create temporary copy of latent_entropy */
362 temp = create_var(long_unsigned_type_node, "temp_latent_entropy");
363
364 /* 2. read... */
365 add_referenced_var(latent_entropy_decl);
366 mark_sym_for_renaming(latent_entropy_decl);
367 assign = gimple_build_assign(temp, latent_entropy_decl);
368 gsi_insert_before(gsi, assign, GSI_NEW_STMT);
369 update_stmt(assign);
370
371 /* 3. ...modify... */
372 op = get_op(NULL);
373 assign = create_assign(op, temp, temp, local_entropy);
374 gsi_insert_after(gsi, assign, GSI_NEW_STMT);
375 update_stmt(assign);
376
377 /* 4. ...write latent_entropy */
378 assign = gimple_build_assign(latent_entropy_decl, temp);
379 gsi_insert_after(gsi, assign, GSI_NEW_STMT);
380 update_stmt(assign);
381 }
382
383 static bool handle_tail_calls(basic_block bb, tree local_entropy)
384 {
385 gimple_stmt_iterator gsi;
386
387 for (gsi = gsi_start_bb(bb); !gsi_end_p(gsi); gsi_next(&gsi)) {
388 gcall *call;
389 gimple stmt = gsi_stmt(gsi);
390
391 if (!is_gimple_call(stmt))
392 continue;
393
394 call = as_a_gcall(stmt);
395 if (!gimple_call_tail_p(call))
396 continue;
397
398 __perturb_latent_entropy(&gsi, local_entropy);
399 return true;
400 }
401
402 return false;
403 }
404
405 static void perturb_latent_entropy(tree local_entropy)
406 {
407 edge_iterator ei;
408 edge e, last_bb_e;
409 basic_block last_bb;
410
411 gcc_assert(single_pred_p(EXIT_BLOCK_PTR_FOR_FN(cfun)));
412 last_bb_e = single_pred_edge(EXIT_BLOCK_PTR_FOR_FN(cfun));
413
414 FOR_EACH_EDGE(e, ei, last_bb_e->src->preds) {
415 if (ENTRY_BLOCK_PTR_FOR_FN(cfun) == e->src)
416 continue;
417 if (EXIT_BLOCK_PTR_FOR_FN(cfun) == e->src)
418 continue;
419
420 handle_tail_calls(e->src, local_entropy);
421 }
422
423 last_bb = single_pred(EXIT_BLOCK_PTR_FOR_FN(cfun));
424 if (!handle_tail_calls(last_bb, local_entropy)) {
425 gimple_stmt_iterator gsi = gsi_last_bb(last_bb);
426
427 __perturb_latent_entropy(&gsi, local_entropy);
428 }
429 }
430
431 static void init_local_entropy(basic_block bb, tree local_entropy)
432 {
433 gimple assign, call;
434 tree frame_addr, rand_const, tmp, fndecl, udi_frame_addr;
435 enum tree_code op;
436 unsigned HOST_WIDE_INT rand_cst;
437 gimple_stmt_iterator gsi = gsi_after_labels(bb);
438
439 /* 1. create local_entropy_frameaddr */
440 frame_addr = create_var(ptr_type_node, "local_entropy_frameaddr");
441
442 /* 2. local_entropy_frameaddr = __builtin_frame_address() */
443 fndecl = builtin_decl_implicit(BUILT_IN_FRAME_ADDRESS);
444 call = gimple_build_call(fndecl, 1, integer_zero_node);
445 gimple_call_set_lhs(call, frame_addr);
446 gsi_insert_before(&gsi, call, GSI_NEW_STMT);
447 update_stmt(call);
448
449 udi_frame_addr = fold_convert(long_unsigned_type_node, frame_addr);
450 assign = gimple_build_assign(local_entropy, udi_frame_addr);
451 gsi_insert_after(&gsi, assign, GSI_NEW_STMT);
452 update_stmt(assign);
453
454 /* 3. create temporary copy of latent_entropy */
455 tmp = create_var(long_unsigned_type_node, "temp_latent_entropy");
456
457 /* 4. read the global entropy variable into local entropy */
458 add_referenced_var(latent_entropy_decl);
459 mark_sym_for_renaming(latent_entropy_decl);
460 assign = gimple_build_assign(tmp, latent_entropy_decl);
461 gsi_insert_after(&gsi, assign, GSI_NEW_STMT);
462 update_stmt(assign);
463
464 /* 5. mix local_entropy_frameaddr into local entropy */
465 assign = create_assign(BIT_XOR_EXPR, local_entropy, local_entropy, tmp);
466 gsi_insert_after(&gsi, assign, GSI_NEW_STMT);
467 update_stmt(assign);
468
469 rand_cst = get_random_const();
470 rand_const = build_int_cstu(long_unsigned_type_node, rand_cst);
471 op = get_op(NULL);
472 assign = create_assign(op, local_entropy, local_entropy, rand_const);
473 gsi_insert_after(&gsi, assign, GSI_NEW_STMT);
474 update_stmt(assign);
475 }
476
477 static bool create_latent_entropy_decl(void)
478 {
479 varpool_node_ptr node;
480
481 if (latent_entropy_decl != NULL_TREE)
482 return true;
483
484 FOR_EACH_VARIABLE(node) {
485 tree name, var = NODE_DECL(node);
486
487 if (DECL_NAME_LENGTH(var) < sizeof("latent_entropy") - 1)
488 continue;
489
490 name = DECL_NAME(var);
491 if (strcmp(IDENTIFIER_POINTER(name), "latent_entropy"))
492 continue;
493
494 latent_entropy_decl = var;
495 break;
496 }
497
498 return latent_entropy_decl != NULL_TREE;
499 }
500
501 static unsigned int latent_entropy_execute(void)
502 {
503 basic_block bb;
504 tree local_entropy;
505
506 if (!create_latent_entropy_decl())
507 return 0;
508
509 /* prepare for step 2 below */
510 gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
511 bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));
512 if (!single_pred_p(bb)) {
513 split_edge(single_succ_edge(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
514 gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
515 bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));
516 }
517
518 /* 1. create the local entropy variable */
519 local_entropy = create_var(long_unsigned_type_node, "local_entropy");
520
521 /* 2. initialize the local entropy variable */
522 init_local_entropy(bb, local_entropy);
523
524 bb = bb->next_bb;
525
526 /*
527 * 3. instrument each BB with an operation on the
528 * local entropy variable
529 */
530 while (bb != EXIT_BLOCK_PTR_FOR_FN(cfun)) {
531 perturb_local_entropy(bb, local_entropy);
532 bb = bb->next_bb;
533 }
534
535 /* 4. mix local entropy into the global entropy variable */
536 perturb_latent_entropy(local_entropy);
537 return 0;
538 }
539
540 static void latent_entropy_start_unit(void *gcc_data __unused,
541 void *user_data __unused)
542 {
543 tree type, id;
544 int quals;
545
546 if (in_lto_p)
547 return;
548
549 /* extern volatile unsigned long latent_entropy */
550 quals = TYPE_QUALS(long_unsigned_type_node) | TYPE_QUAL_VOLATILE;
551 type = build_qualified_type(long_unsigned_type_node, quals);
552 id = get_identifier("latent_entropy");
553 latent_entropy_decl = build_decl(UNKNOWN_LOCATION, VAR_DECL, id, type);
554
555 TREE_STATIC(latent_entropy_decl) = 1;
556 TREE_PUBLIC(latent_entropy_decl) = 1;
557 TREE_USED(latent_entropy_decl) = 1;
558 DECL_PRESERVE_P(latent_entropy_decl) = 1;
559 TREE_THIS_VOLATILE(latent_entropy_decl) = 1;
560 DECL_EXTERNAL(latent_entropy_decl) = 1;
561 DECL_ARTIFICIAL(latent_entropy_decl) = 1;
562 lang_hooks.decls.pushdecl(latent_entropy_decl);
563 }
564
565 #define PASS_NAME latent_entropy
566 #define PROPERTIES_REQUIRED PROP_gimple_leh | PROP_cfg
567 #define TODO_FLAGS_FINISH TODO_verify_ssa | TODO_verify_stmts | TODO_dump_func \
568 | TODO_update_ssa
569 #include "gcc-generate-gimple-pass.h"
570
571 __visible int plugin_init(struct plugin_name_args *plugin_info,
572 struct plugin_gcc_version *version)
573 {
574 bool enabled = true;
575 const char * const plugin_name = plugin_info->base_name;
576 const int argc = plugin_info->argc;
577 const struct plugin_argument * const argv = plugin_info->argv;
578 int i;
579
580 /*
581 * Call get_random_seed() with noinit=true, so that this returns
582 * 0 in the case where no seed has been passed via -frandom-seed.
583 */
584 deterministic_seed = get_random_seed(true);
585
586 static const struct ggc_root_tab gt_ggc_r_gt_latent_entropy[] = {
587 {
588 .base = &latent_entropy_decl,
589 .nelt = 1,
590 .stride = sizeof(latent_entropy_decl),
591 .cb = >_ggc_mx_tree_node,
592 .pchw = >_pch_nx_tree_node
593 },
594 LAST_GGC_ROOT_TAB
595 };
596
597 PASS_INFO(latent_entropy, "optimized", 1, PASS_POS_INSERT_BEFORE);
598
599 if (!plugin_default_version_check(version, &gcc_version)) {
600 error(G_("incompatible gcc/plugin versions"));
601 return 1;
602 }
603
604 for (i = 0; i < argc; ++i) {
605 if (!(strcmp(argv[i].key, "disable"))) {
606 enabled = false;
607 continue;
608 }
609 error(G_("unknown option '-fplugin-arg-%s-%s'"), plugin_name, argv[i].key);
610 }
611
612 register_callback(plugin_name, PLUGIN_INFO, NULL,
613 &latent_entropy_plugin_info);
614 if (enabled) {
615 register_callback(plugin_name, PLUGIN_START_UNIT,
616 &latent_entropy_start_unit, NULL);
617 register_callback(plugin_name, PLUGIN_REGISTER_GGC_ROOTS,
618 NULL, (void *)>_ggc_r_gt_latent_entropy);
619 register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL,
620 &latent_entropy_pass_info);
621 }
622 register_callback(plugin_name, PLUGIN_ATTRIBUTES, register_attributes,
623 NULL);
624
625 return 0;
626 }
627
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