1 /*
2 * Copyright 2011-2017 by the PaX Team <pageexec@freemail.hu>
3 * Modified by Alexander Popov <alex.popov@linux.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 is needed for tracking the lowest border of the kernel stack.
12 * It instruments the kernel code inserting stackleak_track_stack() calls:
13 * - after alloca();
14 * - for the functions with a stack frame size greater than or equal
15 * to the "track-min-size" plugin parameter.
16 *
17 * This plugin is ported from grsecurity/PaX. For more information see:
18 * https://grsecurity.net/
19 * https://pax.grsecurity.net/
20 *
21 * Debugging:
22 * - use fprintf() to stderr, debug_generic_expr(), debug_gimple_stmt(),
23 * print_rtl_single() and debug_rtx();
24 * - add "-fdump-tree-all -fdump-rtl-all" to the plugin CFLAGS in
25 * Makefile.gcc-plugins to see the verbose dumps of the gcc passes;
26 * - use gcc -E to understand the preprocessing shenanigans;
27 * - use gcc with enabled CFG/GIMPLE/SSA verification (--enable-checking).
28 */
29
30 #include "gcc-common.h"
31
32 __visible int plugin_is_GPL_compatible;
33
34 static int track_frame_size = -1;
35 static bool build_for_x86 = false;
36 static const char track_function[] = "stackleak_track_stack";
37 static bool disable = false;
38 static bool verbose = false;
39
40 /*
41 * Mark these global variables (roots) for gcc garbage collector since
42 * they point to the garbage-collected memory.
43 */
44 static GTY(()) tree track_function_decl;
45
46 static struct plugin_info stackleak_plugin_info = {
47 .version = "201707101337",
48 .help = "track-min-size=nn\ttrack stack for functions with a stack frame size >= nn bytes\n"
49 "arch=target_arch\tspecify target build arch\n"
50 "disable\t\tdo not activate the plugin\n"
51 "verbose\t\tprint info about the instrumentation\n"
52 };
53
add_stack_tracking_gcall(gimple_stmt_iterator * gsi,bool after)54 static void add_stack_tracking_gcall(gimple_stmt_iterator *gsi, bool after)
55 {
56 gimple stmt;
57 gcall *gimple_call;
58 cgraph_node_ptr node;
59 basic_block bb;
60
61 /* Insert calling stackleak_track_stack() */
62 stmt = gimple_build_call(track_function_decl, 0);
63 gimple_call = as_a_gcall(stmt);
64 if (after)
65 gsi_insert_after(gsi, gimple_call, GSI_CONTINUE_LINKING);
66 else
67 gsi_insert_before(gsi, gimple_call, GSI_SAME_STMT);
68
69 /* Update the cgraph */
70 bb = gimple_bb(gimple_call);
71 node = cgraph_get_create_node(track_function_decl);
72 gcc_assert(node);
73 cgraph_create_edge(cgraph_get_node(current_function_decl), node,
74 gimple_call, bb->count,
75 compute_call_stmt_bb_frequency(current_function_decl, bb));
76 }
77
is_alloca(gimple stmt)78 static bool is_alloca(gimple stmt)
79 {
80 if (gimple_call_builtin_p(stmt, BUILT_IN_ALLOCA))
81 return true;
82
83 #if BUILDING_GCC_VERSION >= 4007
84 if (gimple_call_builtin_p(stmt, BUILT_IN_ALLOCA_WITH_ALIGN))
85 return true;
86 #endif
87
88 return false;
89 }
90
get_current_stack_pointer_decl(void)91 static tree get_current_stack_pointer_decl(void)
92 {
93 varpool_node_ptr node;
94
95 FOR_EACH_VARIABLE(node) {
96 tree var = NODE_DECL(node);
97 tree name = DECL_NAME(var);
98
99 if (DECL_NAME_LENGTH(var) != sizeof("current_stack_pointer") - 1)
100 continue;
101
102 if (strcmp(IDENTIFIER_POINTER(name), "current_stack_pointer"))
103 continue;
104
105 return var;
106 }
107
108 if (verbose) {
109 fprintf(stderr, "stackleak: missing current_stack_pointer in %s()\n",
110 DECL_NAME_POINTER(current_function_decl));
111 }
112 return NULL_TREE;
113 }
114
add_stack_tracking_gasm(gimple_stmt_iterator * gsi,bool after)115 static void add_stack_tracking_gasm(gimple_stmt_iterator *gsi, bool after)
116 {
117 gasm *asm_call = NULL;
118 tree sp_decl, input;
119 vec<tree, va_gc> *inputs = NULL;
120
121 /* 'no_caller_saved_registers' is currently supported only for x86 */
122 gcc_assert(build_for_x86);
123
124 /*
125 * Insert calling stackleak_track_stack() in asm:
126 * asm volatile("call stackleak_track_stack"
127 * :: "r" (current_stack_pointer))
128 * Use ASM_CALL_CONSTRAINT trick from arch/x86/include/asm/asm.h.
129 * This constraint is taken into account during gcc shrink-wrapping
130 * optimization. It is needed to be sure that stackleak_track_stack()
131 * call is inserted after the prologue of the containing function,
132 * when the stack frame is prepared.
133 */
134 sp_decl = get_current_stack_pointer_decl();
135 if (sp_decl == NULL_TREE) {
136 add_stack_tracking_gcall(gsi, after);
137 return;
138 }
139 input = build_tree_list(NULL_TREE, build_const_char_string(2, "r"));
140 input = chainon(NULL_TREE, build_tree_list(input, sp_decl));
141 vec_safe_push(inputs, input);
142 asm_call = gimple_build_asm_vec("call stackleak_track_stack",
143 inputs, NULL, NULL, NULL);
144 gimple_asm_set_volatile(asm_call, true);
145 if (after)
146 gsi_insert_after(gsi, asm_call, GSI_CONTINUE_LINKING);
147 else
148 gsi_insert_before(gsi, asm_call, GSI_SAME_STMT);
149 update_stmt(asm_call);
150 }
151
add_stack_tracking(gimple_stmt_iterator * gsi,bool after)152 static void add_stack_tracking(gimple_stmt_iterator *gsi, bool after)
153 {
154 /*
155 * The 'no_caller_saved_registers' attribute is used for
156 * stackleak_track_stack(). If the compiler supports this attribute for
157 * the target arch, we can add calling stackleak_track_stack() in asm.
158 * That improves performance: we avoid useless operations with the
159 * caller-saved registers in the functions from which we will remove
160 * stackleak_track_stack() call during the stackleak_cleanup pass.
161 */
162 if (lookup_attribute_spec(get_identifier("no_caller_saved_registers")))
163 add_stack_tracking_gasm(gsi, after);
164 else
165 add_stack_tracking_gcall(gsi, after);
166 }
167
168 /*
169 * Work with the GIMPLE representation of the code. Insert the
170 * stackleak_track_stack() call after alloca() and into the beginning
171 * of the function if it is not instrumented.
172 */
stackleak_instrument_execute(void)173 static unsigned int stackleak_instrument_execute(void)
174 {
175 basic_block bb, entry_bb;
176 bool prologue_instrumented = false, is_leaf = true;
177 gimple_stmt_iterator gsi = { 0 };
178
179 /*
180 * ENTRY_BLOCK_PTR is a basic block which represents possible entry
181 * point of a function. This block does not contain any code and
182 * has a CFG edge to its successor.
183 */
184 gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
185 entry_bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));
186
187 /*
188 * Loop through the GIMPLE statements in each of cfun basic blocks.
189 * cfun is a global variable which represents the function that is
190 * currently processed.
191 */
192 FOR_EACH_BB_FN(bb, cfun) {
193 for (gsi = gsi_start_bb(bb); !gsi_end_p(gsi); gsi_next(&gsi)) {
194 gimple stmt;
195
196 stmt = gsi_stmt(gsi);
197
198 /* Leaf function is a function which makes no calls */
199 if (is_gimple_call(stmt))
200 is_leaf = false;
201
202 if (!is_alloca(stmt))
203 continue;
204
205 if (verbose) {
206 fprintf(stderr, "stackleak: be careful, alloca() in %s()\n",
207 DECL_NAME_POINTER(current_function_decl));
208 }
209
210 /* Insert stackleak_track_stack() call after alloca() */
211 add_stack_tracking(&gsi, true);
212 if (bb == entry_bb)
213 prologue_instrumented = true;
214 }
215 }
216
217 if (prologue_instrumented)
218 return 0;
219
220 /*
221 * Special cases to skip the instrumentation.
222 *
223 * Taking the address of static inline functions materializes them,
224 * but we mustn't instrument some of them as the resulting stack
225 * alignment required by the function call ABI will break other
226 * assumptions regarding the expected (but not otherwise enforced)
227 * register clobbering ABI.
228 *
229 * Case in point: native_save_fl on amd64 when optimized for size
230 * clobbers rdx if it were instrumented here.
231 *
232 * TODO: any more special cases?
233 */
234 if (is_leaf &&
235 !TREE_PUBLIC(current_function_decl) &&
236 DECL_DECLARED_INLINE_P(current_function_decl)) {
237 return 0;
238 }
239
240 if (is_leaf &&
241 !strncmp(IDENTIFIER_POINTER(DECL_NAME(current_function_decl)),
242 "_paravirt_", 10)) {
243 return 0;
244 }
245
246 /* Insert stackleak_track_stack() call at the function beginning */
247 bb = entry_bb;
248 if (!single_pred_p(bb)) {
249 /* gcc_assert(bb_loop_depth(bb) ||
250 (bb->flags & BB_IRREDUCIBLE_LOOP)); */
251 split_edge(single_succ_edge(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
252 gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
253 bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));
254 }
255 gsi = gsi_after_labels(bb);
256 add_stack_tracking(&gsi, false);
257
258 return 0;
259 }
260
large_stack_frame(void)261 static bool large_stack_frame(void)
262 {
263 #if BUILDING_GCC_VERSION >= 8000
264 return maybe_ge(get_frame_size(), track_frame_size);
265 #else
266 return (get_frame_size() >= track_frame_size);
267 #endif
268 }
269
remove_stack_tracking_gcall(void)270 static void remove_stack_tracking_gcall(void)
271 {
272 rtx_insn *insn, *next;
273
274 /*
275 * Find stackleak_track_stack() calls. Loop through the chain of insns,
276 * which is an RTL representation of the code for a function.
277 *
278 * The example of a matching insn:
279 * (call_insn 8 4 10 2 (call (mem (symbol_ref ("stackleak_track_stack")
280 * [flags 0x41] <function_decl 0x7f7cd3302a80 stackleak_track_stack>)
281 * [0 stackleak_track_stack S1 A8]) (0)) 675 {*call} (expr_list
282 * (symbol_ref ("stackleak_track_stack") [flags 0x41] <function_decl
283 * 0x7f7cd3302a80 stackleak_track_stack>) (expr_list (0) (nil))) (nil))
284 */
285 for (insn = get_insns(); insn; insn = next) {
286 rtx body;
287
288 next = NEXT_INSN(insn);
289
290 /* Check the expression code of the insn */
291 if (!CALL_P(insn))
292 continue;
293
294 /*
295 * Check the expression code of the insn body, which is an RTL
296 * Expression (RTX) describing the side effect performed by
297 * that insn.
298 */
299 body = PATTERN(insn);
300
301 if (GET_CODE(body) == PARALLEL)
302 body = XVECEXP(body, 0, 0);
303
304 if (GET_CODE(body) != CALL)
305 continue;
306
307 /*
308 * Check the first operand of the call expression. It should
309 * be a mem RTX describing the needed subroutine with a
310 * symbol_ref RTX.
311 */
312 body = XEXP(body, 0);
313 if (GET_CODE(body) != MEM)
314 continue;
315
316 body = XEXP(body, 0);
317 if (GET_CODE(body) != SYMBOL_REF)
318 continue;
319
320 if (SYMBOL_REF_DECL(body) != track_function_decl)
321 continue;
322
323 /* Delete the stackleak_track_stack() call */
324 delete_insn_and_edges(insn);
325 #if BUILDING_GCC_VERSION >= 4007 && BUILDING_GCC_VERSION < 8000
326 if (GET_CODE(next) == NOTE &&
327 NOTE_KIND(next) == NOTE_INSN_CALL_ARG_LOCATION) {
328 insn = next;
329 next = NEXT_INSN(insn);
330 delete_insn_and_edges(insn);
331 }
332 #endif
333 }
334 }
335
remove_stack_tracking_gasm(void)336 static bool remove_stack_tracking_gasm(void)
337 {
338 bool removed = false;
339 rtx_insn *insn, *next;
340
341 /* 'no_caller_saved_registers' is currently supported only for x86 */
342 gcc_assert(build_for_x86);
343
344 /*
345 * Find stackleak_track_stack() asm calls. Loop through the chain of
346 * insns, which is an RTL representation of the code for a function.
347 *
348 * The example of a matching insn:
349 * (insn 11 5 12 2 (parallel [ (asm_operands/v
350 * ("call stackleak_track_stack") ("") 0
351 * [ (reg/v:DI 7 sp [ current_stack_pointer ]) ]
352 * [ (asm_input:DI ("r")) ] [])
353 * (clobber (reg:CC 17 flags)) ]) -1 (nil))
354 */
355 for (insn = get_insns(); insn; insn = next) {
356 rtx body;
357
358 next = NEXT_INSN(insn);
359
360 /* Check the expression code of the insn */
361 if (!NONJUMP_INSN_P(insn))
362 continue;
363
364 /*
365 * Check the expression code of the insn body, which is an RTL
366 * Expression (RTX) describing the side effect performed by
367 * that insn.
368 */
369 body = PATTERN(insn);
370
371 if (GET_CODE(body) != PARALLEL)
372 continue;
373
374 body = XVECEXP(body, 0, 0);
375
376 if (GET_CODE(body) != ASM_OPERANDS)
377 continue;
378
379 if (strcmp(ASM_OPERANDS_TEMPLATE(body),
380 "call stackleak_track_stack")) {
381 continue;
382 }
383
384 delete_insn_and_edges(insn);
385 gcc_assert(!removed);
386 removed = true;
387 }
388
389 return removed;
390 }
391
392 /*
393 * Work with the RTL representation of the code.
394 * Remove the unneeded stackleak_track_stack() calls from the functions
395 * which don't call alloca() and don't have a large enough stack frame size.
396 */
stackleak_cleanup_execute(void)397 static unsigned int stackleak_cleanup_execute(void)
398 {
399 const char *fn = DECL_NAME_POINTER(current_function_decl);
400 bool removed = false;
401
402 /*
403 * Leave stack tracking in functions that call alloca().
404 * Additional case:
405 * gcc before version 7 called allocate_dynamic_stack_space() from
406 * expand_stack_vars() for runtime alignment of constant-sized stack
407 * variables. That caused cfun->calls_alloca to be set for functions
408 * that in fact don't use alloca().
409 * For more info see gcc commit 7072df0aae0c59ae437e.
410 * Let's leave such functions instrumented as well.
411 */
412 if (cfun->calls_alloca) {
413 if (verbose)
414 fprintf(stderr, "stackleak: instrument %s(): calls_alloca\n", fn);
415 return 0;
416 }
417
418 /* Leave stack tracking in functions with large stack frame */
419 if (large_stack_frame()) {
420 if (verbose)
421 fprintf(stderr, "stackleak: instrument %s()\n", fn);
422 return 0;
423 }
424
425 if (lookup_attribute_spec(get_identifier("no_caller_saved_registers")))
426 removed = remove_stack_tracking_gasm();
427
428 if (!removed)
429 remove_stack_tracking_gcall();
430
431 return 0;
432 }
433
434 /*
435 * STRING_CST may or may not be NUL terminated:
436 * https://gcc.gnu.org/onlinedocs/gccint/Constant-expressions.html
437 */
string_equal(tree node,const char * string,int length)438 static inline bool string_equal(tree node, const char *string, int length)
439 {
440 if (TREE_STRING_LENGTH(node) < length)
441 return false;
442 if (TREE_STRING_LENGTH(node) > length + 1)
443 return false;
444 if (TREE_STRING_LENGTH(node) == length + 1 &&
445 TREE_STRING_POINTER(node)[length] != '\0')
446 return false;
447 return !memcmp(TREE_STRING_POINTER(node), string, length);
448 }
449 #define STRING_EQUAL(node, str) string_equal(node, str, strlen(str))
450
stackleak_gate(void)451 static bool stackleak_gate(void)
452 {
453 tree section;
454
455 section = lookup_attribute("section",
456 DECL_ATTRIBUTES(current_function_decl));
457 if (section && TREE_VALUE(section)) {
458 section = TREE_VALUE(TREE_VALUE(section));
459
460 if (STRING_EQUAL(section, ".init.text"))
461 return false;
462 if (STRING_EQUAL(section, ".devinit.text"))
463 return false;
464 if (STRING_EQUAL(section, ".cpuinit.text"))
465 return false;
466 if (STRING_EQUAL(section, ".meminit.text"))
467 return false;
468 }
469
470 return track_frame_size >= 0;
471 }
472
473 /* Build the function declaration for stackleak_track_stack() */
stackleak_start_unit(void * gcc_data __unused,void * user_data __unused)474 static void stackleak_start_unit(void *gcc_data __unused,
475 void *user_data __unused)
476 {
477 tree fntype;
478
479 /* void stackleak_track_stack(void) */
480 fntype = build_function_type_list(void_type_node, NULL_TREE);
481 track_function_decl = build_fn_decl(track_function, fntype);
482 DECL_ASSEMBLER_NAME(track_function_decl); /* for LTO */
483 TREE_PUBLIC(track_function_decl) = 1;
484 TREE_USED(track_function_decl) = 1;
485 DECL_EXTERNAL(track_function_decl) = 1;
486 DECL_ARTIFICIAL(track_function_decl) = 1;
487 DECL_PRESERVE_P(track_function_decl) = 1;
488 }
489
490 /*
491 * Pass gate function is a predicate function that gets executed before the
492 * corresponding pass. If the return value is 'true' the pass gets executed,
493 * otherwise, it is skipped.
494 */
stackleak_instrument_gate(void)495 static bool stackleak_instrument_gate(void)
496 {
497 return stackleak_gate();
498 }
499
500 #define PASS_NAME stackleak_instrument
501 #define PROPERTIES_REQUIRED PROP_gimple_leh | PROP_cfg
502 #define TODO_FLAGS_START TODO_verify_ssa | TODO_verify_flow | TODO_verify_stmts
503 #define TODO_FLAGS_FINISH TODO_verify_ssa | TODO_verify_stmts | TODO_dump_func \
504 | TODO_update_ssa | TODO_rebuild_cgraph_edges
505 #include "gcc-generate-gimple-pass.h"
506
stackleak_cleanup_gate(void)507 static bool stackleak_cleanup_gate(void)
508 {
509 return stackleak_gate();
510 }
511
512 #define PASS_NAME stackleak_cleanup
513 #define TODO_FLAGS_FINISH TODO_dump_func
514 #include "gcc-generate-rtl-pass.h"
515
516 /*
517 * Every gcc plugin exports a plugin_init() function that is called right
518 * after the plugin is loaded. This function is responsible for registering
519 * the plugin callbacks and doing other required initialization.
520 */
plugin_init(struct plugin_name_args * plugin_info,struct plugin_gcc_version * version)521 __visible int plugin_init(struct plugin_name_args *plugin_info,
522 struct plugin_gcc_version *version)
523 {
524 const char * const plugin_name = plugin_info->base_name;
525 const int argc = plugin_info->argc;
526 const struct plugin_argument * const argv = plugin_info->argv;
527 int i = 0;
528
529 /* Extra GGC root tables describing our GTY-ed data */
530 static const struct ggc_root_tab gt_ggc_r_gt_stackleak[] = {
531 {
532 .base = &track_function_decl,
533 .nelt = 1,
534 .stride = sizeof(track_function_decl),
535 .cb = >_ggc_mx_tree_node,
536 .pchw = >_pch_nx_tree_node
537 },
538 LAST_GGC_ROOT_TAB
539 };
540
541 /*
542 * The stackleak_instrument pass should be executed before the
543 * "optimized" pass, which is the control flow graph cleanup that is
544 * performed just before expanding gcc trees to the RTL. In former
545 * versions of the plugin this new pass was inserted before the
546 * "tree_profile" pass, which is currently called "profile".
547 */
548 PASS_INFO(stackleak_instrument, "optimized", 1,
549 PASS_POS_INSERT_BEFORE);
550
551 /*
552 * The stackleak_cleanup pass should be executed before the "*free_cfg"
553 * pass. It's the moment when the stack frame size is already final,
554 * function prologues and epilogues are generated, and the
555 * machine-dependent code transformations are not done.
556 */
557 PASS_INFO(stackleak_cleanup, "*free_cfg", 1, PASS_POS_INSERT_BEFORE);
558
559 if (!plugin_default_version_check(version, &gcc_version)) {
560 error(G_("incompatible gcc/plugin versions"));
561 return 1;
562 }
563
564 /* Parse the plugin arguments */
565 for (i = 0; i < argc; i++) {
566 if (!strcmp(argv[i].key, "track-min-size")) {
567 if (!argv[i].value) {
568 error(G_("no value supplied for option '-fplugin-arg-%s-%s'"),
569 plugin_name, argv[i].key);
570 return 1;
571 }
572
573 track_frame_size = atoi(argv[i].value);
574 if (track_frame_size < 0) {
575 error(G_("invalid option argument '-fplugin-arg-%s-%s=%s'"),
576 plugin_name, argv[i].key, argv[i].value);
577 return 1;
578 }
579 } else if (!strcmp(argv[i].key, "arch")) {
580 if (!argv[i].value) {
581 error(G_("no value supplied for option '-fplugin-arg-%s-%s'"),
582 plugin_name, argv[i].key);
583 return 1;
584 }
585
586 if (!strcmp(argv[i].value, "x86"))
587 build_for_x86 = true;
588 } else if (!strcmp(argv[i].key, "disable")) {
589 disable = true;
590 } else if (!strcmp(argv[i].key, "verbose")) {
591 verbose = true;
592 } else {
593 error(G_("unknown option '-fplugin-arg-%s-%s'"),
594 plugin_name, argv[i].key);
595 return 1;
596 }
597 }
598
599 if (disable) {
600 if (verbose)
601 fprintf(stderr, "stackleak: disabled for this translation unit\n");
602 return 0;
603 }
604
605 /* Give the information about the plugin */
606 register_callback(plugin_name, PLUGIN_INFO, NULL,
607 &stackleak_plugin_info);
608
609 /* Register to be called before processing a translation unit */
610 register_callback(plugin_name, PLUGIN_START_UNIT,
611 &stackleak_start_unit, NULL);
612
613 /* Register an extra GCC garbage collector (GGC) root table */
614 register_callback(plugin_name, PLUGIN_REGISTER_GGC_ROOTS, NULL,
615 (void *)>_ggc_r_gt_stackleak);
616
617 /*
618 * Hook into the Pass Manager to register new gcc passes.
619 *
620 * The stack frame size info is available only at the last RTL pass,
621 * when it's too late to insert complex code like a function call.
622 * So we register two gcc passes to instrument every function at first
623 * and remove the unneeded instrumentation later.
624 */
625 register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL,
626 &stackleak_instrument_pass_info);
627 register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL,
628 &stackleak_cleanup_pass_info);
629
630 return 0;
631 }
632