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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
260static void register_attributes(void *event_data __unused, void *data __unused)
261{
262 latent_entropy_attr.name = "latent_entropy";
263 latent_entropy_attr.decl_required = true;
264 latent_entropy_attr.handler = handle_latent_entropy_attribute;
265
266 register_attribute(&latent_entropy_attr);
267}
268
269static bool latent_entropy_gate(void)
270{
271 tree list;
272
273 /* don't bother with noreturn functions for now */
274 if (TREE_THIS_VOLATILE(current_function_decl))
275 return false;
276
277 /* gcc-4.5 doesn't discover some trivial noreturn functions */
278 if (EDGE_COUNT(EXIT_BLOCK_PTR_FOR_FN(cfun)->preds) == 0)
279 return false;
280
281 list = DECL_ATTRIBUTES(current_function_decl);
282 return lookup_attribute("latent_entropy", list) != NULL_TREE;
283}
284
285static tree create_var(tree type, const char *name)
286{
287 tree var;
288
289 var = create_tmp_var(type, name);
290 add_referenced_var(var);
291 mark_sym_for_renaming(var);
292 return var;
293}
294
295/*
296 * Set up the next operation and its constant operand to use in the latent
297 * entropy PRNG. When RHS is specified, the request is for perturbing the
298 * local latent entropy variable, otherwise it is for perturbing the global
299 * latent entropy variable where the two operands are already given by the
300 * local and global latent entropy variables themselves.
301 *
302 * The operation is one of add/xor/rol when instrumenting the local entropy
303 * variable and one of add/xor when perturbing the global entropy variable.
304 * Rotation is not used for the latter case because it would transmit less
305 * entropy to the global variable than the other two operations.
306 */
307static enum tree_code get_op(tree *rhs)
308{
309 static enum tree_code op;
310 unsigned HOST_WIDE_INT random_const;
311
312 random_const = get_random_const();
313
314 switch (op) {
315 case BIT_XOR_EXPR:
316 op = PLUS_EXPR;
317 break;
318
319 case PLUS_EXPR:
320 if (rhs) {
321 op = LROTATE_EXPR;
322 /*
323 * This code limits the value of random_const to
324 * the size of a long for the rotation
325 */
326 random_const %= TYPE_PRECISION(long_unsigned_type_node);
327 break;
328 }
329
330 case LROTATE_EXPR:
331 default:
332 op = BIT_XOR_EXPR;
333 break;
334 }
335 if (rhs)
336 *rhs = build_int_cstu(long_unsigned_type_node, random_const);
337 return op;
338}
339
340static gimple create_assign(enum tree_code code, tree lhs, tree op1,
341 tree op2)
342{
343 return gimple_build_assign_with_ops(code, lhs, op1, op2);
344}
345
346static void perturb_local_entropy(basic_block bb, tree local_entropy)
347{
348 gimple_stmt_iterator gsi;
349 gimple assign;
350 tree rhs;
351 enum tree_code op;
352
353 op = get_op(&rhs);
354 assign = create_assign(op, local_entropy, local_entropy, rhs);
355 gsi = gsi_after_labels(bb);
356 gsi_insert_before(&gsi, assign, GSI_NEW_STMT);
357 update_stmt(assign);
358}
359
360static void __perturb_latent_entropy(gimple_stmt_iterator *gsi,
361 tree local_entropy)
362{
363 gimple assign;
364 tree temp;
365 enum tree_code op;
366
367 /* 1. create temporary copy of latent_entropy */
368 temp = create_var(long_unsigned_type_node, "temp_latent_entropy");
369
370 /* 2. read... */
371 add_referenced_var(latent_entropy_decl);
372 mark_sym_for_renaming(latent_entropy_decl);
373 assign = gimple_build_assign(temp, latent_entropy_decl);
374 gsi_insert_before(gsi, assign, GSI_NEW_STMT);
375 update_stmt(assign);
376
377 /* 3. ...modify... */
378 op = get_op(NULL);
379 assign = create_assign(op, temp, temp, local_entropy);
380 gsi_insert_after(gsi, assign, GSI_NEW_STMT);
381 update_stmt(assign);
382
383 /* 4. ...write latent_entropy */
384 assign = gimple_build_assign(latent_entropy_decl, temp);
385 gsi_insert_after(gsi, assign, GSI_NEW_STMT);
386 update_stmt(assign);
387}
388
389static bool handle_tail_calls(basic_block bb, tree local_entropy)
390{
391 gimple_stmt_iterator gsi;
392
393 for (gsi = gsi_start_bb(bb); !gsi_end_p(gsi); gsi_next(&gsi)) {
394 gcall *call;
395 gimple stmt = gsi_stmt(gsi);
396
397 if (!is_gimple_call(stmt))
398 continue;
399
400 call = as_a_gcall(stmt);
401 if (!gimple_call_tail_p(call))
402 continue;
403
404 __perturb_latent_entropy(&gsi, local_entropy);
405 return true;
406 }
407
408 return false;
409}
410
411static void perturb_latent_entropy(tree local_entropy)
412{
413 edge_iterator ei;
414 edge e, last_bb_e;
415 basic_block last_bb;
416
417 gcc_assert(single_pred_p(EXIT_BLOCK_PTR_FOR_FN(cfun)));
418 last_bb_e = single_pred_edge(EXIT_BLOCK_PTR_FOR_FN(cfun));
419
420 FOR_EACH_EDGE(e, ei, last_bb_e->src->preds) {
421 if (ENTRY_BLOCK_PTR_FOR_FN(cfun) == e->src)
422 continue;
423 if (EXIT_BLOCK_PTR_FOR_FN(cfun) == e->src)
424 continue;
425
426 handle_tail_calls(e->src, local_entropy);
427 }
428
429 last_bb = single_pred(EXIT_BLOCK_PTR_FOR_FN(cfun));
430 if (!handle_tail_calls(last_bb, local_entropy)) {
431 gimple_stmt_iterator gsi = gsi_last_bb(last_bb);
432
433 __perturb_latent_entropy(&gsi, local_entropy);
434 }
435}
436
437static void init_local_entropy(basic_block bb, tree local_entropy)
438{
439 gimple assign, call;
440 tree frame_addr, rand_const, tmp, fndecl, udi_frame_addr;
441 enum tree_code op;
442 unsigned HOST_WIDE_INT rand_cst;
443 gimple_stmt_iterator gsi = gsi_after_labels(bb);
444
445 /* 1. create local_entropy_frameaddr */
446 frame_addr = create_var(ptr_type_node, "local_entropy_frameaddr");
447
448 /* 2. local_entropy_frameaddr = __builtin_frame_address() */
449 fndecl = builtin_decl_implicit(BUILT_IN_FRAME_ADDRESS);
450 call = gimple_build_call(fndecl, 1, integer_zero_node);
451 gimple_call_set_lhs(call, frame_addr);
452 gsi_insert_before(&gsi, call, GSI_NEW_STMT);
453 update_stmt(call);
454
455 udi_frame_addr = fold_convert(long_unsigned_type_node, frame_addr);
456 assign = gimple_build_assign(local_entropy, udi_frame_addr);
457 gsi_insert_after(&gsi, assign, GSI_NEW_STMT);
458 update_stmt(assign);
459
460 /* 3. create temporary copy of latent_entropy */
461 tmp = create_var(long_unsigned_type_node, "temp_latent_entropy");
462
463 /* 4. read the global entropy variable into local entropy */
464 add_referenced_var(latent_entropy_decl);
465 mark_sym_for_renaming(latent_entropy_decl);
466 assign = gimple_build_assign(tmp, latent_entropy_decl);
467 gsi_insert_after(&gsi, assign, GSI_NEW_STMT);
468 update_stmt(assign);
469
470 /* 5. mix local_entropy_frameaddr into local entropy */
471 assign = create_assign(BIT_XOR_EXPR, local_entropy, local_entropy, tmp);
472 gsi_insert_after(&gsi, assign, GSI_NEW_STMT);
473 update_stmt(assign);
474
475 rand_cst = get_random_const();
476 rand_const = build_int_cstu(long_unsigned_type_node, rand_cst);
477 op = get_op(NULL);
478 assign = create_assign(op, local_entropy, local_entropy, rand_const);
479 gsi_insert_after(&gsi, assign, GSI_NEW_STMT);
480 update_stmt(assign);
481}
482
483static bool create_latent_entropy_decl(void)
484{
485 varpool_node_ptr node;
486
487 if (latent_entropy_decl != NULL_TREE)
488 return true;
489
490 FOR_EACH_VARIABLE(node) {
491 tree name, var = NODE_DECL(node);
492
493 if (DECL_NAME_LENGTH(var) < sizeof("latent_entropy") - 1)
494 continue;
495
496 name = DECL_NAME(var);
497 if (strcmp(IDENTIFIER_POINTER(name), "latent_entropy"))
498 continue;
499
500 latent_entropy_decl = var;
501 break;
502 }
503
504 return latent_entropy_decl != NULL_TREE;
505}
506
507static unsigned int latent_entropy_execute(void)
508{
509 basic_block bb;
510 tree local_entropy;
511
512 if (!create_latent_entropy_decl())
513 return 0;
514
515 /* prepare for step 2 below */
516 gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
517 bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));
518 if (!single_pred_p(bb)) {
519 split_edge(single_succ_edge(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
520 gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
521 bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));
522 }
523
524 /* 1. create the local entropy variable */
525 local_entropy = create_var(long_unsigned_type_node, "local_entropy");
526
527 /* 2. initialize the local entropy variable */
528 init_local_entropy(bb, local_entropy);
529
530 bb = bb->next_bb;
531
532 /*
533 * 3. instrument each BB with an operation on the
534 * local entropy variable
535 */
536 while (bb != EXIT_BLOCK_PTR_FOR_FN(cfun)) {
537 perturb_local_entropy(bb, local_entropy);
538 bb = bb->next_bb;
539 };
540
541 /* 4. mix local entropy into the global entropy variable */
542 perturb_latent_entropy(local_entropy);
543 return 0;
544}
545
546static void latent_entropy_start_unit(void *gcc_data __unused,
547 void *user_data __unused)
548{
549 tree type, id;
550 int quals;
551
552 seed = get_random_seed(false);
553
554 if (in_lto_p)
555 return;
556
557 /* extern volatile unsigned long latent_entropy */
558 quals = TYPE_QUALS(long_unsigned_type_node) | TYPE_QUAL_VOLATILE;
559 type = build_qualified_type(long_unsigned_type_node, quals);
560 id = get_identifier("latent_entropy");
561 latent_entropy_decl = build_decl(UNKNOWN_LOCATION, VAR_DECL, id, type);
562
563 TREE_STATIC(latent_entropy_decl) = 1;
564 TREE_PUBLIC(latent_entropy_decl) = 1;
565 TREE_USED(latent_entropy_decl) = 1;
566 DECL_PRESERVE_P(latent_entropy_decl) = 1;
567 TREE_THIS_VOLATILE(latent_entropy_decl) = 1;
568 DECL_EXTERNAL(latent_entropy_decl) = 1;
569 DECL_ARTIFICIAL(latent_entropy_decl) = 1;
570 lang_hooks.decls.pushdecl(latent_entropy_decl);
571}
572
573#define PASS_NAME latent_entropy
574#define PROPERTIES_REQUIRED PROP_gimple_leh | PROP_cfg
575#define TODO_FLAGS_FINISH TODO_verify_ssa | TODO_verify_stmts | TODO_dump_func \
576 | TODO_update_ssa
577#include "gcc-generate-gimple-pass.h"
578
579__visible int plugin_init(struct plugin_name_args *plugin_info,
580 struct plugin_gcc_version *version)
581{
582 bool enabled = true;
583 const char * const plugin_name = plugin_info->base_name;
584 const int argc = plugin_info->argc;
585 const struct plugin_argument * const argv = plugin_info->argv;
586 int i;
587
588 static const struct ggc_root_tab gt_ggc_r_gt_latent_entropy[] = {
589 {
590 .base = &latent_entropy_decl,
591 .nelt = 1,
592 .stride = sizeof(latent_entropy_decl),
593 .cb = >_ggc_mx_tree_node,
594 .pchw = >_pch_nx_tree_node
595 },
596 LAST_GGC_ROOT_TAB
597 };
598
599 PASS_INFO(latent_entropy, "optimized", 1, PASS_POS_INSERT_BEFORE);
600
601 if (!plugin_default_version_check(version, &gcc_version)) {
602 error(G_("incompatible gcc/plugin versions"));
603 return 1;
604 }
605
606 for (i = 0; i < argc; ++i) {
607 if (!(strcmp(argv[i].key, "disable"))) {
608 enabled = false;
609 continue;
610 }
611 error(G_("unknown option '-fplugin-arg-%s-%s'"), plugin_name, argv[i].key);
612 }
613
614 register_callback(plugin_name, PLUGIN_INFO, NULL,
615 &latent_entropy_plugin_info);
616 if (enabled) {
617 register_callback(plugin_name, PLUGIN_START_UNIT,
618 &latent_entropy_start_unit, NULL);
619 register_callback(plugin_name, PLUGIN_REGISTER_GGC_ROOTS,
620 NULL, (void *)>_ggc_r_gt_latent_entropy);
621 register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL,
622 &latent_entropy_pass_info);
623 }
624 register_callback(plugin_name, PLUGIN_ATTRIBUTES, register_attributes,
625 NULL);
626
627 return 0;
628}