1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Copyright 2011-2017 by the PaX Team <pageexec@freemail.hu>
4 * Modified by Alexander Popov <alex.popov@linux.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 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 = PLUGIN_VERSION,
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 (gimple_call_builtin_p(stmt, BUILT_IN_ALLOCA_WITH_ALIGN))
84 return true;
85
86 return false;
87 }
88
get_current_stack_pointer_decl(void)89 static tree get_current_stack_pointer_decl(void)
90 {
91 varpool_node_ptr node;
92
93 FOR_EACH_VARIABLE(node) {
94 tree var = NODE_DECL(node);
95 tree name = DECL_NAME(var);
96
97 if (DECL_NAME_LENGTH(var) != sizeof("current_stack_pointer") - 1)
98 continue;
99
100 if (strcmp(IDENTIFIER_POINTER(name), "current_stack_pointer"))
101 continue;
102
103 return var;
104 }
105
106 if (verbose) {
107 fprintf(stderr, "stackleak: missing current_stack_pointer in %s()\n",
108 DECL_NAME_POINTER(current_function_decl));
109 }
110 return NULL_TREE;
111 }
112
add_stack_tracking_gasm(gimple_stmt_iterator * gsi,bool after)113 static void add_stack_tracking_gasm(gimple_stmt_iterator *gsi, bool after)
114 {
115 gasm *asm_call = NULL;
116 tree sp_decl, input;
117 vec<tree, va_gc> *inputs = NULL;
118
119 /* 'no_caller_saved_registers' is currently supported only for x86 */
120 gcc_assert(build_for_x86);
121
122 /*
123 * Insert calling stackleak_track_stack() in asm:
124 * asm volatile("call stackleak_track_stack"
125 * :: "r" (current_stack_pointer))
126 * Use ASM_CALL_CONSTRAINT trick from arch/x86/include/asm/asm.h.
127 * This constraint is taken into account during gcc shrink-wrapping
128 * optimization. It is needed to be sure that stackleak_track_stack()
129 * call is inserted after the prologue of the containing function,
130 * when the stack frame is prepared.
131 */
132 sp_decl = get_current_stack_pointer_decl();
133 if (sp_decl == NULL_TREE) {
134 add_stack_tracking_gcall(gsi, after);
135 return;
136 }
137 input = build_tree_list(NULL_TREE, build_const_char_string(2, "r"));
138 input = chainon(NULL_TREE, build_tree_list(input, sp_decl));
139 vec_safe_push(inputs, input);
140 asm_call = gimple_build_asm_vec("call stackleak_track_stack",
141 inputs, NULL, NULL, NULL);
142 gimple_asm_set_volatile(asm_call, true);
143 if (after)
144 gsi_insert_after(gsi, asm_call, GSI_CONTINUE_LINKING);
145 else
146 gsi_insert_before(gsi, asm_call, GSI_SAME_STMT);
147 update_stmt(asm_call);
148 }
149
add_stack_tracking(gimple_stmt_iterator * gsi,bool after)150 static void add_stack_tracking(gimple_stmt_iterator *gsi, bool after)
151 {
152 /*
153 * The 'no_caller_saved_registers' attribute is used for
154 * stackleak_track_stack(). If the compiler supports this attribute for
155 * the target arch, we can add calling stackleak_track_stack() in asm.
156 * That improves performance: we avoid useless operations with the
157 * caller-saved registers in the functions from which we will remove
158 * stackleak_track_stack() call during the stackleak_cleanup pass.
159 */
160 if (lookup_attribute_spec(get_identifier("no_caller_saved_registers")))
161 add_stack_tracking_gasm(gsi, after);
162 else
163 add_stack_tracking_gcall(gsi, after);
164 }
165
166 /*
167 * Work with the GIMPLE representation of the code. Insert the
168 * stackleak_track_stack() call after alloca() and into the beginning
169 * of the function if it is not instrumented.
170 */
stackleak_instrument_execute(void)171 static unsigned int stackleak_instrument_execute(void)
172 {
173 basic_block bb, entry_bb;
174 bool prologue_instrumented = false, is_leaf = true;
175 gimple_stmt_iterator gsi = { 0 };
176
177 /*
178 * ENTRY_BLOCK_PTR is a basic block which represents possible entry
179 * point of a function. This block does not contain any code and
180 * has a CFG edge to its successor.
181 */
182 gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
183 entry_bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));
184
185 /*
186 * Loop through the GIMPLE statements in each of cfun basic blocks.
187 * cfun is a global variable which represents the function that is
188 * currently processed.
189 */
190 FOR_EACH_BB_FN(bb, cfun) {
191 for (gsi = gsi_start_bb(bb); !gsi_end_p(gsi); gsi_next(&gsi)) {
192 gimple stmt;
193
194 stmt = gsi_stmt(gsi);
195
196 /* Leaf function is a function which makes no calls */
197 if (is_gimple_call(stmt))
198 is_leaf = false;
199
200 if (!is_alloca(stmt))
201 continue;
202
203 if (verbose) {
204 fprintf(stderr, "stackleak: be careful, alloca() in %s()\n",
205 DECL_NAME_POINTER(current_function_decl));
206 }
207
208 /* Insert stackleak_track_stack() call after alloca() */
209 add_stack_tracking(&gsi, true);
210 if (bb == entry_bb)
211 prologue_instrumented = true;
212 }
213 }
214
215 if (prologue_instrumented)
216 return 0;
217
218 /*
219 * Special cases to skip the instrumentation.
220 *
221 * Taking the address of static inline functions materializes them,
222 * but we mustn't instrument some of them as the resulting stack
223 * alignment required by the function call ABI will break other
224 * assumptions regarding the expected (but not otherwise enforced)
225 * register clobbering ABI.
226 *
227 * Case in point: native_save_fl on amd64 when optimized for size
228 * clobbers rdx if it were instrumented here.
229 *
230 * TODO: any more special cases?
231 */
232 if (is_leaf &&
233 !TREE_PUBLIC(current_function_decl) &&
234 DECL_DECLARED_INLINE_P(current_function_decl)) {
235 return 0;
236 }
237
238 if (is_leaf &&
239 !strncmp(IDENTIFIER_POINTER(DECL_NAME(current_function_decl)),
240 "_paravirt_", 10)) {
241 return 0;
242 }
243
244 /* Insert stackleak_track_stack() call at the function beginning */
245 bb = entry_bb;
246 if (!single_pred_p(bb)) {
247 /* gcc_assert(bb_loop_depth(bb) ||
248 (bb->flags & BB_IRREDUCIBLE_LOOP)); */
249 split_edge(single_succ_edge(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
250 gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
251 bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));
252 }
253 gsi = gsi_after_labels(bb);
254 add_stack_tracking(&gsi, false);
255
256 return 0;
257 }
258
large_stack_frame(void)259 static bool large_stack_frame(void)
260 {
261 #if BUILDING_GCC_VERSION >= 8000
262 return maybe_ge(get_frame_size(), track_frame_size);
263 #else
264 return (get_frame_size() >= track_frame_size);
265 #endif
266 }
267
remove_stack_tracking_gcall(void)268 static void remove_stack_tracking_gcall(void)
269 {
270 rtx_insn *insn, *next;
271
272 /*
273 * Find stackleak_track_stack() calls. Loop through the chain of insns,
274 * which is an RTL representation of the code for a function.
275 *
276 * The example of a matching insn:
277 * (call_insn 8 4 10 2 (call (mem (symbol_ref ("stackleak_track_stack")
278 * [flags 0x41] <function_decl 0x7f7cd3302a80 stackleak_track_stack>)
279 * [0 stackleak_track_stack S1 A8]) (0)) 675 {*call} (expr_list
280 * (symbol_ref ("stackleak_track_stack") [flags 0x41] <function_decl
281 * 0x7f7cd3302a80 stackleak_track_stack>) (expr_list (0) (nil))) (nil))
282 */
283 for (insn = get_insns(); insn; insn = next) {
284 rtx body;
285
286 next = NEXT_INSN(insn);
287
288 /* Check the expression code of the insn */
289 if (!CALL_P(insn))
290 continue;
291
292 /*
293 * Check the expression code of the insn body, which is an RTL
294 * Expression (RTX) describing the side effect performed by
295 * that insn.
296 */
297 body = PATTERN(insn);
298
299 if (GET_CODE(body) == PARALLEL)
300 body = XVECEXP(body, 0, 0);
301
302 if (GET_CODE(body) != CALL)
303 continue;
304
305 /*
306 * Check the first operand of the call expression. It should
307 * be a mem RTX describing the needed subroutine with a
308 * symbol_ref RTX.
309 */
310 body = XEXP(body, 0);
311 if (GET_CODE(body) != MEM)
312 continue;
313
314 body = XEXP(body, 0);
315 if (GET_CODE(body) != SYMBOL_REF)
316 continue;
317
318 if (SYMBOL_REF_DECL(body) != track_function_decl)
319 continue;
320
321 /* Delete the stackleak_track_stack() call */
322 delete_insn_and_edges(insn);
323 #if BUILDING_GCC_VERSION < 8000
324 if (GET_CODE(next) == NOTE &&
325 NOTE_KIND(next) == NOTE_INSN_CALL_ARG_LOCATION) {
326 insn = next;
327 next = NEXT_INSN(insn);
328 delete_insn_and_edges(insn);
329 }
330 #endif
331 }
332 }
333
remove_stack_tracking_gasm(void)334 static bool remove_stack_tracking_gasm(void)
335 {
336 bool removed = false;
337 rtx_insn *insn, *next;
338
339 /* 'no_caller_saved_registers' is currently supported only for x86 */
340 gcc_assert(build_for_x86);
341
342 /*
343 * Find stackleak_track_stack() asm calls. Loop through the chain of
344 * insns, which is an RTL representation of the code for a function.
345 *
346 * The example of a matching insn:
347 * (insn 11 5 12 2 (parallel [ (asm_operands/v
348 * ("call stackleak_track_stack") ("") 0
349 * [ (reg/v:DI 7 sp [ current_stack_pointer ]) ]
350 * [ (asm_input:DI ("r")) ] [])
351 * (clobber (reg:CC 17 flags)) ]) -1 (nil))
352 */
353 for (insn = get_insns(); insn; insn = next) {
354 rtx body;
355
356 next = NEXT_INSN(insn);
357
358 /* Check the expression code of the insn */
359 if (!NONJUMP_INSN_P(insn))
360 continue;
361
362 /*
363 * Check the expression code of the insn body, which is an RTL
364 * Expression (RTX) describing the side effect performed by
365 * that insn.
366 */
367 body = PATTERN(insn);
368
369 if (GET_CODE(body) != PARALLEL)
370 continue;
371
372 body = XVECEXP(body, 0, 0);
373
374 if (GET_CODE(body) != ASM_OPERANDS)
375 continue;
376
377 if (strcmp(ASM_OPERANDS_TEMPLATE(body),
378 "call stackleak_track_stack")) {
379 continue;
380 }
381
382 delete_insn_and_edges(insn);
383 gcc_assert(!removed);
384 removed = true;
385 }
386
387 return removed;
388 }
389
390 /*
391 * Work with the RTL representation of the code.
392 * Remove the unneeded stackleak_track_stack() calls from the functions
393 * which don't call alloca() and don't have a large enough stack frame size.
394 */
stackleak_cleanup_execute(void)395 static unsigned int stackleak_cleanup_execute(void)
396 {
397 const char *fn = DECL_NAME_POINTER(current_function_decl);
398 bool removed = false;
399
400 /*
401 * Leave stack tracking in functions that call alloca().
402 * Additional case:
403 * gcc before version 7 called allocate_dynamic_stack_space() from
404 * expand_stack_vars() for runtime alignment of constant-sized stack
405 * variables. That caused cfun->calls_alloca to be set for functions
406 * that in fact don't use alloca().
407 * For more info see gcc commit 7072df0aae0c59ae437e.
408 * Let's leave such functions instrumented as well.
409 */
410 if (cfun->calls_alloca) {
411 if (verbose)
412 fprintf(stderr, "stackleak: instrument %s(): calls_alloca\n", fn);
413 return 0;
414 }
415
416 /* Leave stack tracking in functions with large stack frame */
417 if (large_stack_frame()) {
418 if (verbose)
419 fprintf(stderr, "stackleak: instrument %s()\n", fn);
420 return 0;
421 }
422
423 if (lookup_attribute_spec(get_identifier("no_caller_saved_registers")))
424 removed = remove_stack_tracking_gasm();
425
426 if (!removed)
427 remove_stack_tracking_gcall();
428
429 return 0;
430 }
431
432 /*
433 * STRING_CST may or may not be NUL terminated:
434 * https://gcc.gnu.org/onlinedocs/gccint/Constant-expressions.html
435 */
string_equal(tree node,const char * string,int length)436 static inline bool string_equal(tree node, const char *string, int length)
437 {
438 if (TREE_STRING_LENGTH(node) < length)
439 return false;
440 if (TREE_STRING_LENGTH(node) > length + 1)
441 return false;
442 if (TREE_STRING_LENGTH(node) == length + 1 &&
443 TREE_STRING_POINTER(node)[length] != '\0')
444 return false;
445 return !memcmp(TREE_STRING_POINTER(node), string, length);
446 }
447 #define STRING_EQUAL(node, str) string_equal(node, str, strlen(str))
448
stackleak_gate(void)449 static bool stackleak_gate(void)
450 {
451 tree section;
452
453 section = lookup_attribute("section",
454 DECL_ATTRIBUTES(current_function_decl));
455 if (section && TREE_VALUE(section)) {
456 section = TREE_VALUE(TREE_VALUE(section));
457
458 if (STRING_EQUAL(section, ".init.text"))
459 return false;
460 if (STRING_EQUAL(section, ".devinit.text"))
461 return false;
462 if (STRING_EQUAL(section, ".cpuinit.text"))
463 return false;
464 if (STRING_EQUAL(section, ".meminit.text"))
465 return false;
466 if (STRING_EQUAL(section, ".noinstr.text"))
467 return false;
468 if (STRING_EQUAL(section, ".entry.text"))
469 return false;
470 if (STRING_EQUAL(section, ".head.text"))
471 return false;
472 }
473
474 return track_frame_size >= 0;
475 }
476
477 /* Build the function declaration for stackleak_track_stack() */
stackleak_start_unit(void * gcc_data __unused,void * user_data __unused)478 static void stackleak_start_unit(void *gcc_data __unused,
479 void *user_data __unused)
480 {
481 tree fntype;
482
483 /* void stackleak_track_stack(void) */
484 fntype = build_function_type_list(void_type_node, NULL_TREE);
485 track_function_decl = build_fn_decl(track_function, fntype);
486 DECL_ASSEMBLER_NAME(track_function_decl); /* for LTO */
487 TREE_PUBLIC(track_function_decl) = 1;
488 TREE_USED(track_function_decl) = 1;
489 DECL_EXTERNAL(track_function_decl) = 1;
490 DECL_ARTIFICIAL(track_function_decl) = 1;
491 DECL_PRESERVE_P(track_function_decl) = 1;
492 }
493
494 /*
495 * Pass gate function is a predicate function that gets executed before the
496 * corresponding pass. If the return value is 'true' the pass gets executed,
497 * otherwise, it is skipped.
498 */
stackleak_instrument_gate(void)499 static bool stackleak_instrument_gate(void)
500 {
501 return stackleak_gate();
502 }
503
504 #define PASS_NAME stackleak_instrument
505 #define PROPERTIES_REQUIRED PROP_gimple_leh | PROP_cfg
506 #define TODO_FLAGS_START TODO_verify_ssa | TODO_verify_flow | TODO_verify_stmts
507 #define TODO_FLAGS_FINISH TODO_verify_ssa | TODO_verify_stmts | TODO_dump_func \
508 | TODO_update_ssa | TODO_rebuild_cgraph_edges
509 #include "gcc-generate-gimple-pass.h"
510
stackleak_cleanup_gate(void)511 static bool stackleak_cleanup_gate(void)
512 {
513 return stackleak_gate();
514 }
515
516 #define PASS_NAME stackleak_cleanup
517 #define TODO_FLAGS_FINISH TODO_dump_func
518 #include "gcc-generate-rtl-pass.h"
519
520 /*
521 * Every gcc plugin exports a plugin_init() function that is called right
522 * after the plugin is loaded. This function is responsible for registering
523 * the plugin callbacks and doing other required initialization.
524 */
plugin_init(struct plugin_name_args * plugin_info,struct plugin_gcc_version * version)525 __visible int plugin_init(struct plugin_name_args *plugin_info,
526 struct plugin_gcc_version *version)
527 {
528 const char * const plugin_name = plugin_info->base_name;
529 const int argc = plugin_info->argc;
530 const struct plugin_argument * const argv = plugin_info->argv;
531 int i = 0;
532
533 /* Extra GGC root tables describing our GTY-ed data */
534 static const struct ggc_root_tab gt_ggc_r_gt_stackleak[] = {
535 {
536 .base = &track_function_decl,
537 .nelt = 1,
538 .stride = sizeof(track_function_decl),
539 .cb = >_ggc_mx_tree_node,
540 .pchw = >_pch_nx_tree_node
541 },
542 LAST_GGC_ROOT_TAB
543 };
544
545 /*
546 * The stackleak_instrument pass should be executed before the
547 * "optimized" pass, which is the control flow graph cleanup that is
548 * performed just before expanding gcc trees to the RTL. In former
549 * versions of the plugin this new pass was inserted before the
550 * "tree_profile" pass, which is currently called "profile".
551 */
552 PASS_INFO(stackleak_instrument, "optimized", 1,
553 PASS_POS_INSERT_BEFORE);
554
555 /*
556 * The stackleak_cleanup pass should be executed before the "*free_cfg"
557 * pass. It's the moment when the stack frame size is already final,
558 * function prologues and epilogues are generated, and the
559 * machine-dependent code transformations are not done.
560 */
561 PASS_INFO(stackleak_cleanup, "*free_cfg", 1, PASS_POS_INSERT_BEFORE);
562
563 if (!plugin_default_version_check(version, &gcc_version)) {
564 error(G_("incompatible gcc/plugin versions"));
565 return 1;
566 }
567
568 /* Parse the plugin arguments */
569 for (i = 0; i < argc; i++) {
570 if (!strcmp(argv[i].key, "track-min-size")) {
571 if (!argv[i].value) {
572 error(G_("no value supplied for option '-fplugin-arg-%s-%s'"),
573 plugin_name, argv[i].key);
574 return 1;
575 }
576
577 track_frame_size = atoi(argv[i].value);
578 if (track_frame_size < 0) {
579 error(G_("invalid option argument '-fplugin-arg-%s-%s=%s'"),
580 plugin_name, argv[i].key, argv[i].value);
581 return 1;
582 }
583 } else if (!strcmp(argv[i].key, "arch")) {
584 if (!argv[i].value) {
585 error(G_("no value supplied for option '-fplugin-arg-%s-%s'"),
586 plugin_name, argv[i].key);
587 return 1;
588 }
589
590 if (!strcmp(argv[i].value, "x86"))
591 build_for_x86 = true;
592 } else if (!strcmp(argv[i].key, "disable")) {
593 disable = true;
594 } else if (!strcmp(argv[i].key, "verbose")) {
595 verbose = true;
596 } else {
597 error(G_("unknown option '-fplugin-arg-%s-%s'"),
598 plugin_name, argv[i].key);
599 return 1;
600 }
601 }
602
603 if (disable) {
604 if (verbose)
605 fprintf(stderr, "stackleak: disabled for this translation unit\n");
606 return 0;
607 }
608
609 /* Give the information about the plugin */
610 register_callback(plugin_name, PLUGIN_INFO, NULL,
611 &stackleak_plugin_info);
612
613 /* Register to be called before processing a translation unit */
614 register_callback(plugin_name, PLUGIN_START_UNIT,
615 &stackleak_start_unit, NULL);
616
617 /* Register an extra GCC garbage collector (GGC) root table */
618 register_callback(plugin_name, PLUGIN_REGISTER_GGC_ROOTS, NULL,
619 (void *)>_ggc_r_gt_stackleak);
620
621 /*
622 * Hook into the Pass Manager to register new gcc passes.
623 *
624 * The stack frame size info is available only at the last RTL pass,
625 * when it's too late to insert complex code like a function call.
626 * So we register two gcc passes to instrument every function at first
627 * and remove the unneeded instrumentation later.
628 */
629 register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL,
630 &stackleak_instrument_pass_info);
631 register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL,
632 &stackleak_cleanup_pass_info);
633
634 return 0;
635 }
636