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1/*
2 * Copyright 2012-2016 by the PaX Team <pageexec@freemail.hu>
3 * Copyright 2016 by Emese Revfy <re.emese@gmail.com>
4 * Licensed under the GPL v2
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, args - 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, args - 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
82static GTY(()) tree latent_entropy_decl;
83
84static struct plugin_info latent_entropy_plugin_info = {
85 .version = "201606141920vanilla",
86 .help = "disable\tturn off latent entropy instrumentation\n",
87};
88
89static unsigned HOST_WIDE_INT seed;
90/*
91 * get_random_seed() (this is a GCC function) generates the seed.
92 * This is a simple random generator without any cryptographic security because
93 * the entropy doesn't come from here.
94 */
95static unsigned HOST_WIDE_INT get_random_const(void)
96{
97 unsigned int i;
98 unsigned HOST_WIDE_INT ret = 0;
99
100 for (i = 0; i < 8 * sizeof(ret); i++) {
101 ret = (ret << 1) | (seed & 1);
102 seed >>= 1;
103 if (ret & 1)
104 seed ^= 0xD800000000000000ULL;
105 }
106
107 return ret;
108}
109
110static tree tree_get_random_const(tree type)
111{
112 unsigned long long mask;
113
114 mask = 1ULL << (TREE_INT_CST_LOW(TYPE_SIZE(type)) - 1);
115 mask = 2 * (mask - 1) + 1;
116
117 if (TYPE_UNSIGNED(type))
118 return build_int_cstu(type, mask & get_random_const());
119 return build_int_cst(type, mask & get_random_const());
120}
121
122static tree handle_latent_entropy_attribute(tree *node, tree name,
123 tree args __unused,
124 int flags __unused,
125 bool *no_add_attrs)
126{
127 tree type;
128#if BUILDING_GCC_VERSION <= 4007
129 VEC(constructor_elt, gc) *vals;
130#else
131 vec<constructor_elt, va_gc> *vals;
132#endif
133
134 switch (TREE_CODE(*node)) {
135 default:
136 *no_add_attrs = true;
137 error("%qE attribute only applies to functions and variables",
138 name);
139 break;
140
141 case VAR_DECL:
142 if (DECL_INITIAL(*node)) {
143 *no_add_attrs = true;
144 error("variable %qD with %qE attribute must not be initialized",
145 *node, name);
146 break;
147 }
148
149 if (!TREE_STATIC(*node)) {
150 *no_add_attrs = true;
151 error("variable %qD with %qE attribute must not be local",
152 *node, name);
153 break;
154 }
155
156 type = TREE_TYPE(*node);
157 switch (TREE_CODE(type)) {
158 default:
159 *no_add_attrs = true;
160 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",
161 *node, name);
162 break;
163
164 case RECORD_TYPE: {
165 tree fld, lst = TYPE_FIELDS(type);
166 unsigned int nelt = 0;
167
168 for (fld = lst; fld; nelt++, fld = TREE_CHAIN(fld)) {
169 tree fieldtype;
170
171 fieldtype = TREE_TYPE(fld);
172 if (TREE_CODE(fieldtype) == INTEGER_TYPE)
173 continue;
174
175 *no_add_attrs = true;
176 error("structure variable %qD with %qE attribute has a non-integer field %qE",
177 *node, name, fld);
178 break;
179 }
180
181 if (fld)
182 break;
183
184#if BUILDING_GCC_VERSION <= 4007
185 vals = VEC_alloc(constructor_elt, gc, nelt);
186#else
187 vec_alloc(vals, nelt);
188#endif
189
190 for (fld = lst; fld; fld = TREE_CHAIN(fld)) {
191 tree random_const, fld_t = TREE_TYPE(fld);
192
193 random_const = tree_get_random_const(fld_t);
194 CONSTRUCTOR_APPEND_ELT(vals, fld, random_const);
195 }
196
197 /* Initialize the fields with random constants */
198 DECL_INITIAL(*node) = build_constructor(type, vals);
199 break;
200 }
201
202 /* Initialize the variable with a random constant */
203 case INTEGER_TYPE:
204 DECL_INITIAL(*node) = tree_get_random_const(type);
205 break;
206
207 case ARRAY_TYPE: {
208 tree elt_type, array_size, elt_size;
209 unsigned int i, nelt;
210 HOST_WIDE_INT array_size_int, elt_size_int;
211
212 elt_type = TREE_TYPE(type);
213 elt_size = TYPE_SIZE_UNIT(TREE_TYPE(type));
214 array_size = TYPE_SIZE_UNIT(type);
215
216 if (TREE_CODE(elt_type) != INTEGER_TYPE || !array_size
217 || TREE_CODE(array_size) != INTEGER_CST) {
218 *no_add_attrs = true;
219 error("array variable %qD with %qE attribute must be a fixed length integer array type",
220 *node, name);
221 break;
222 }
223
224 array_size_int = TREE_INT_CST_LOW(array_size);
225 elt_size_int = TREE_INT_CST_LOW(elt_size);
226 nelt = array_size_int / elt_size_int;
227
228#if BUILDING_GCC_VERSION <= 4007
229 vals = VEC_alloc(constructor_elt, gc, nelt);
230#else
231 vec_alloc(vals, nelt);
232#endif
233
234 for (i = 0; i < nelt; i++) {
235 tree cst = size_int(i);
236 tree rand_cst = tree_get_random_const(elt_type);
237
238 CONSTRUCTOR_APPEND_ELT(vals, cst, rand_cst);
239 }
240
241 /*
242 * Initialize the elements of the array with random
243 * constants
244 */
245 DECL_INITIAL(*node) = build_constructor(type, vals);
246 break;
247 }
248 }
249 break;
250
251 case FUNCTION_DECL:
252 break;
253 }
254
255 return NULL_TREE;
256}
257
258static struct attribute_spec latent_entropy_attr = {
259 .name = "latent_entropy",
260 .min_length = 0,
261 .max_length = 0,
262 .decl_required = true,
263 .type_required = false,
264 .function_type_required = false,
265 .handler = handle_latent_entropy_attribute,
266#if BUILDING_GCC_VERSION >= 4007
267 .affects_type_identity = false
268#endif
269};
270
271static void register_attributes(void *event_data __unused, void *data __unused)
272{
273 register_attribute(&latent_entropy_attr);
274}
275
276static bool latent_entropy_gate(void)
277{
278 tree list;
279
280 /* don't bother with noreturn functions for now */
281 if (TREE_THIS_VOLATILE(current_function_decl))
282 return false;
283
284 /* gcc-4.5 doesn't discover some trivial noreturn functions */
285 if (EDGE_COUNT(EXIT_BLOCK_PTR_FOR_FN(cfun)->preds) == 0)
286 return false;
287
288 list = DECL_ATTRIBUTES(current_function_decl);
289 return lookup_attribute("latent_entropy", list) != NULL_TREE;
290}
291
292static tree create_var(tree type, const char *name)
293{
294 tree var;
295
296 var = create_tmp_var(type, name);
297 add_referenced_var(var);
298 mark_sym_for_renaming(var);
299 return var;
300}
301
302/*
303 * Set up the next operation and its constant operand to use in the latent
304 * entropy PRNG. When RHS is specified, the request is for perturbing the
305 * local latent entropy variable, otherwise it is for perturbing the global
306 * latent entropy variable where the two operands are already given by the
307 * local and global latent entropy variables themselves.
308 *
309 * The operation is one of add/xor/rol when instrumenting the local entropy
310 * variable and one of add/xor when perturbing the global entropy variable.
311 * Rotation is not used for the latter case because it would transmit less
312 * entropy to the global variable than the other two operations.
313 */
314static enum tree_code get_op(tree *rhs)
315{
316 static enum tree_code op;
317 unsigned HOST_WIDE_INT random_const;
318
319 random_const = get_random_const();
320
321 switch (op) {
322 case BIT_XOR_EXPR:
323 op = PLUS_EXPR;
324 break;
325
326 case PLUS_EXPR:
327 if (rhs) {
328 op = LROTATE_EXPR;
329 /*
330 * This code limits the value of random_const to
331 * the size of a long for the rotation
332 */
333 random_const %= TYPE_PRECISION(long_unsigned_type_node);
334 break;
335 }
336
337 case LROTATE_EXPR:
338 default:
339 op = BIT_XOR_EXPR;
340 break;
341 }
342 if (rhs)
343 *rhs = build_int_cstu(long_unsigned_type_node, random_const);
344 return op;
345}
346
347static gimple create_assign(enum tree_code code, tree lhs, tree op1,
348 tree op2)
349{
350 return gimple_build_assign_with_ops(code, lhs, op1, op2);
351}
352
353static void perturb_local_entropy(basic_block bb, tree local_entropy)
354{
355 gimple_stmt_iterator gsi;
356 gimple assign;
357 tree rhs;
358 enum tree_code op;
359
360 op = get_op(&rhs);
361 assign = create_assign(op, local_entropy, local_entropy, rhs);
362 gsi = gsi_after_labels(bb);
363 gsi_insert_before(&gsi, assign, GSI_NEW_STMT);
364 update_stmt(assign);
365}
366
367static void __perturb_latent_entropy(gimple_stmt_iterator *gsi,
368 tree local_entropy)
369{
370 gimple assign;
371 tree temp;
372 enum tree_code op;
373
374 /* 1. create temporary copy of latent_entropy */
375 temp = create_var(long_unsigned_type_node, "temp_latent_entropy");
376
377 /* 2. read... */
378 add_referenced_var(latent_entropy_decl);
379 mark_sym_for_renaming(latent_entropy_decl);
380 assign = gimple_build_assign(temp, latent_entropy_decl);
381 gsi_insert_before(gsi, assign, GSI_NEW_STMT);
382 update_stmt(assign);
383
384 /* 3. ...modify... */
385 op = get_op(NULL);
386 assign = create_assign(op, temp, temp, local_entropy);
387 gsi_insert_after(gsi, assign, GSI_NEW_STMT);
388 update_stmt(assign);
389
390 /* 4. ...write latent_entropy */
391 assign = gimple_build_assign(latent_entropy_decl, temp);
392 gsi_insert_after(gsi, assign, GSI_NEW_STMT);
393 update_stmt(assign);
394}
395
396static bool handle_tail_calls(basic_block bb, tree local_entropy)
397{
398 gimple_stmt_iterator gsi;
399
400 for (gsi = gsi_start_bb(bb); !gsi_end_p(gsi); gsi_next(&gsi)) {
401 gcall *call;
402 gimple stmt = gsi_stmt(gsi);
403
404 if (!is_gimple_call(stmt))
405 continue;
406
407 call = as_a_gcall(stmt);
408 if (!gimple_call_tail_p(call))
409 continue;
410
411 __perturb_latent_entropy(&gsi, local_entropy);
412 return true;
413 }
414
415 return false;
416}
417
418static void perturb_latent_entropy(tree local_entropy)
419{
420 edge_iterator ei;
421 edge e, last_bb_e;
422 basic_block last_bb;
423
424 gcc_assert(single_pred_p(EXIT_BLOCK_PTR_FOR_FN(cfun)));
425 last_bb_e = single_pred_edge(EXIT_BLOCK_PTR_FOR_FN(cfun));
426
427 FOR_EACH_EDGE(e, ei, last_bb_e->src->preds) {
428 if (ENTRY_BLOCK_PTR_FOR_FN(cfun) == e->src)
429 continue;
430 if (EXIT_BLOCK_PTR_FOR_FN(cfun) == e->src)
431 continue;
432
433 handle_tail_calls(e->src, local_entropy);
434 }
435
436 last_bb = single_pred(EXIT_BLOCK_PTR_FOR_FN(cfun));
437 if (!handle_tail_calls(last_bb, local_entropy)) {
438 gimple_stmt_iterator gsi = gsi_last_bb(last_bb);
439
440 __perturb_latent_entropy(&gsi, local_entropy);
441 }
442}
443
444static void init_local_entropy(basic_block bb, tree local_entropy)
445{
446 gimple assign, call;
447 tree frame_addr, rand_const, tmp, fndecl, udi_frame_addr;
448 enum tree_code op;
449 unsigned HOST_WIDE_INT rand_cst;
450 gimple_stmt_iterator gsi = gsi_after_labels(bb);
451
452 /* 1. create local_entropy_frameaddr */
453 frame_addr = create_var(ptr_type_node, "local_entropy_frameaddr");
454
455 /* 2. local_entropy_frameaddr = __builtin_frame_address() */
456 fndecl = builtin_decl_implicit(BUILT_IN_FRAME_ADDRESS);
457 call = gimple_build_call(fndecl, 1, integer_zero_node);
458 gimple_call_set_lhs(call, frame_addr);
459 gsi_insert_before(&gsi, call, GSI_NEW_STMT);
460 update_stmt(call);
461
462 udi_frame_addr = fold_convert(long_unsigned_type_node, frame_addr);
463 assign = gimple_build_assign(local_entropy, udi_frame_addr);
464 gsi_insert_after(&gsi, assign, GSI_NEW_STMT);
465 update_stmt(assign);
466
467 /* 3. create temporary copy of latent_entropy */
468 tmp = create_var(long_unsigned_type_node, "temp_latent_entropy");
469
470 /* 4. read the global entropy variable into local entropy */
471 add_referenced_var(latent_entropy_decl);
472 mark_sym_for_renaming(latent_entropy_decl);
473 assign = gimple_build_assign(tmp, latent_entropy_decl);
474 gsi_insert_after(&gsi, assign, GSI_NEW_STMT);
475 update_stmt(assign);
476
477 /* 5. mix local_entropy_frameaddr into local entropy */
478 assign = create_assign(BIT_XOR_EXPR, local_entropy, local_entropy, tmp);
479 gsi_insert_after(&gsi, assign, GSI_NEW_STMT);
480 update_stmt(assign);
481
482 rand_cst = get_random_const();
483 rand_const = build_int_cstu(long_unsigned_type_node, rand_cst);
484 op = get_op(NULL);
485 assign = create_assign(op, local_entropy, local_entropy, rand_const);
486 gsi_insert_after(&gsi, assign, GSI_NEW_STMT);
487 update_stmt(assign);
488}
489
490static bool create_latent_entropy_decl(void)
491{
492 varpool_node_ptr node;
493
494 if (latent_entropy_decl != NULL_TREE)
495 return true;
496
497 FOR_EACH_VARIABLE(node) {
498 tree name, var = NODE_DECL(node);
499
500 if (DECL_NAME_LENGTH(var) < sizeof("latent_entropy") - 1)
501 continue;
502
503 name = DECL_NAME(var);
504 if (strcmp(IDENTIFIER_POINTER(name), "latent_entropy"))
505 continue;
506
507 latent_entropy_decl = var;
508 break;
509 }
510
511 return latent_entropy_decl != NULL_TREE;
512}
513
514static unsigned int latent_entropy_execute(void)
515{
516 basic_block bb;
517 tree local_entropy;
518
519 if (!create_latent_entropy_decl())
520 return 0;
521
522 /* prepare for step 2 below */
523 gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
524 bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));
525 if (!single_pred_p(bb)) {
526 split_edge(single_succ_edge(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
527 gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
528 bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));
529 }
530
531 /* 1. create the local entropy variable */
532 local_entropy = create_var(long_unsigned_type_node, "local_entropy");
533
534 /* 2. initialize the local entropy variable */
535 init_local_entropy(bb, local_entropy);
536
537 bb = bb->next_bb;
538
539 /*
540 * 3. instrument each BB with an operation on the
541 * local entropy variable
542 */
543 while (bb != EXIT_BLOCK_PTR_FOR_FN(cfun)) {
544 perturb_local_entropy(bb, local_entropy);
545 bb = bb->next_bb;
546 };
547
548 /* 4. mix local entropy into the global entropy variable */
549 perturb_latent_entropy(local_entropy);
550 return 0;
551}
552
553static void latent_entropy_start_unit(void *gcc_data __unused,
554 void *user_data __unused)
555{
556 tree type, id;
557 int quals;
558
559 seed = get_random_seed(false);
560
561 if (in_lto_p)
562 return;
563
564 /* extern volatile unsigned long latent_entropy */
565 quals = TYPE_QUALS(long_unsigned_type_node) | TYPE_QUAL_VOLATILE;
566 type = build_qualified_type(long_unsigned_type_node, quals);
567 id = get_identifier("latent_entropy");
568 latent_entropy_decl = build_decl(UNKNOWN_LOCATION, VAR_DECL, id, type);
569
570 TREE_STATIC(latent_entropy_decl) = 1;
571 TREE_PUBLIC(latent_entropy_decl) = 1;
572 TREE_USED(latent_entropy_decl) = 1;
573 DECL_PRESERVE_P(latent_entropy_decl) = 1;
574 TREE_THIS_VOLATILE(latent_entropy_decl) = 1;
575 DECL_EXTERNAL(latent_entropy_decl) = 1;
576 DECL_ARTIFICIAL(latent_entropy_decl) = 1;
577 lang_hooks.decls.pushdecl(latent_entropy_decl);
578}
579
580#define PASS_NAME latent_entropy
581#define PROPERTIES_REQUIRED PROP_gimple_leh | PROP_cfg
582#define TODO_FLAGS_FINISH TODO_verify_ssa | TODO_verify_stmts | TODO_dump_func \
583 | TODO_update_ssa
584#include "gcc-generate-gimple-pass.h"
585
586__visible int plugin_init(struct plugin_name_args *plugin_info,
587 struct plugin_gcc_version *version)
588{
589 bool enabled = true;
590 const char * const plugin_name = plugin_info->base_name;
591 const int argc = plugin_info->argc;
592 const struct plugin_argument * const argv = plugin_info->argv;
593 int i;
594
595 struct register_pass_info latent_entropy_pass_info;
596
597 latent_entropy_pass_info.pass = make_latent_entropy_pass();
598 latent_entropy_pass_info.reference_pass_name = "optimized";
599 latent_entropy_pass_info.ref_pass_instance_number = 1;
600 latent_entropy_pass_info.pos_op = PASS_POS_INSERT_BEFORE;
601 static const struct ggc_root_tab gt_ggc_r_gt_latent_entropy[] = {
602 {
603 .base = &latent_entropy_decl,
604 .nelt = 1,
605 .stride = sizeof(latent_entropy_decl),
606 .cb = >_ggc_mx_tree_node,
607 .pchw = >_pch_nx_tree_node
608 },
609 LAST_GGC_ROOT_TAB
610 };
611
612 if (!plugin_default_version_check(version, &gcc_version)) {
613 error(G_("incompatible gcc/plugin versions"));
614 return 1;
615 }
616
617 for (i = 0; i < argc; ++i) {
618 if (!(strcmp(argv[i].key, "disable"))) {
619 enabled = false;
620 continue;
621 }
622 error(G_("unknown option '-fplugin-arg-%s-%s'"), plugin_name, argv[i].key);
623 }
624
625 register_callback(plugin_name, PLUGIN_INFO, NULL,
626 &latent_entropy_plugin_info);
627 if (enabled) {
628 register_callback(plugin_name, PLUGIN_START_UNIT,
629 &latent_entropy_start_unit, NULL);
630 register_callback(plugin_name, PLUGIN_REGISTER_GGC_ROOTS,
631 NULL, (void *)>_ggc_r_gt_latent_entropy);
632 register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL,
633 &latent_entropy_pass_info);
634 }
635 register_callback(plugin_name, PLUGIN_ATTRIBUTES, register_attributes,
636 NULL);
637
638 return 0;
639}