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10e9ae9f AP |
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() and print_simple_rtl(); | |
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 const char track_function[] = "stackleak_track_stack"; | |
36 | ||
37 | /* | |
38 | * Mark these global variables (roots) for gcc garbage collector since | |
39 | * they point to the garbage-collected memory. | |
40 | */ | |
41 | static GTY(()) tree track_function_decl; | |
42 | ||
43 | static struct plugin_info stackleak_plugin_info = { | |
44 | .version = "201707101337", | |
45 | .help = "track-min-size=nn\ttrack stack for functions with a stack frame size >= nn bytes\n" | |
46 | "disable\t\tdo not activate the plugin\n" | |
47 | }; | |
48 | ||
49 | static void stackleak_add_track_stack(gimple_stmt_iterator *gsi, bool after) | |
50 | { | |
51 | gimple stmt; | |
52 | gcall *stackleak_track_stack; | |
53 | cgraph_node_ptr node; | |
54 | int frequency; | |
55 | basic_block bb; | |
56 | ||
57 | /* Insert call to void stackleak_track_stack(void) */ | |
58 | stmt = gimple_build_call(track_function_decl, 0); | |
59 | stackleak_track_stack = as_a_gcall(stmt); | |
60 | if (after) { | |
61 | gsi_insert_after(gsi, stackleak_track_stack, | |
62 | GSI_CONTINUE_LINKING); | |
63 | } else { | |
64 | gsi_insert_before(gsi, stackleak_track_stack, GSI_SAME_STMT); | |
65 | } | |
66 | ||
67 | /* Update the cgraph */ | |
68 | bb = gimple_bb(stackleak_track_stack); | |
69 | node = cgraph_get_create_node(track_function_decl); | |
70 | gcc_assert(node); | |
71 | frequency = compute_call_stmt_bb_frequency(current_function_decl, bb); | |
72 | cgraph_create_edge(cgraph_get_node(current_function_decl), node, | |
73 | stackleak_track_stack, bb->count, frequency); | |
74 | } | |
75 | ||
76 | static bool is_alloca(gimple stmt) | |
77 | { | |
78 | if (gimple_call_builtin_p(stmt, BUILT_IN_ALLOCA)) | |
79 | return true; | |
80 | ||
81 | #if BUILDING_GCC_VERSION >= 4007 | |
82 | if (gimple_call_builtin_p(stmt, BUILT_IN_ALLOCA_WITH_ALIGN)) | |
83 | return true; | |
84 | #endif | |
85 | ||
86 | return false; | |
87 | } | |
88 | ||
89 | /* | |
90 | * Work with the GIMPLE representation of the code. Insert the | |
91 | * stackleak_track_stack() call after alloca() and into the beginning | |
92 | * of the function if it is not instrumented. | |
93 | */ | |
94 | static unsigned int stackleak_instrument_execute(void) | |
95 | { | |
96 | basic_block bb, entry_bb; | |
97 | bool prologue_instrumented = false, is_leaf = true; | |
98 | gimple_stmt_iterator gsi; | |
99 | ||
100 | /* | |
101 | * ENTRY_BLOCK_PTR is a basic block which represents possible entry | |
102 | * point of a function. This block does not contain any code and | |
103 | * has a CFG edge to its successor. | |
104 | */ | |
105 | gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun))); | |
106 | entry_bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun)); | |
107 | ||
108 | /* | |
109 | * Loop through the GIMPLE statements in each of cfun basic blocks. | |
110 | * cfun is a global variable which represents the function that is | |
111 | * currently processed. | |
112 | */ | |
113 | FOR_EACH_BB_FN(bb, cfun) { | |
114 | for (gsi = gsi_start_bb(bb); !gsi_end_p(gsi); gsi_next(&gsi)) { | |
115 | gimple stmt; | |
116 | ||
117 | stmt = gsi_stmt(gsi); | |
118 | ||
119 | /* Leaf function is a function which makes no calls */ | |
120 | if (is_gimple_call(stmt)) | |
121 | is_leaf = false; | |
122 | ||
123 | if (!is_alloca(stmt)) | |
124 | continue; | |
125 | ||
126 | /* Insert stackleak_track_stack() call after alloca() */ | |
127 | stackleak_add_track_stack(&gsi, true); | |
128 | if (bb == entry_bb) | |
129 | prologue_instrumented = true; | |
130 | } | |
131 | } | |
132 | ||
133 | if (prologue_instrumented) | |
134 | return 0; | |
135 | ||
136 | /* | |
137 | * Special cases to skip the instrumentation. | |
138 | * | |
139 | * Taking the address of static inline functions materializes them, | |
140 | * but we mustn't instrument some of them as the resulting stack | |
141 | * alignment required by the function call ABI will break other | |
142 | * assumptions regarding the expected (but not otherwise enforced) | |
143 | * register clobbering ABI. | |
144 | * | |
145 | * Case in point: native_save_fl on amd64 when optimized for size | |
146 | * clobbers rdx if it were instrumented here. | |
147 | * | |
148 | * TODO: any more special cases? | |
149 | */ | |
150 | if (is_leaf && | |
151 | !TREE_PUBLIC(current_function_decl) && | |
152 | DECL_DECLARED_INLINE_P(current_function_decl)) { | |
153 | return 0; | |
154 | } | |
155 | ||
156 | if (is_leaf && | |
157 | !strncmp(IDENTIFIER_POINTER(DECL_NAME(current_function_decl)), | |
158 | "_paravirt_", 10)) { | |
159 | return 0; | |
160 | } | |
161 | ||
162 | /* Insert stackleak_track_stack() call at the function beginning */ | |
163 | bb = entry_bb; | |
164 | if (!single_pred_p(bb)) { | |
165 | /* gcc_assert(bb_loop_depth(bb) || | |
166 | (bb->flags & BB_IRREDUCIBLE_LOOP)); */ | |
167 | split_edge(single_succ_edge(ENTRY_BLOCK_PTR_FOR_FN(cfun))); | |
168 | gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun))); | |
169 | bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun)); | |
170 | } | |
171 | gsi = gsi_after_labels(bb); | |
172 | stackleak_add_track_stack(&gsi, false); | |
173 | ||
174 | return 0; | |
175 | } | |
176 | ||
177 | static bool large_stack_frame(void) | |
178 | { | |
179 | #if BUILDING_GCC_VERSION >= 8000 | |
180 | return maybe_ge(get_frame_size(), track_frame_size); | |
181 | #else | |
182 | return (get_frame_size() >= track_frame_size); | |
183 | #endif | |
184 | } | |
185 | ||
186 | /* | |
187 | * Work with the RTL representation of the code. | |
188 | * Remove the unneeded stackleak_track_stack() calls from the functions | |
189 | * which don't call alloca() and don't have a large enough stack frame size. | |
190 | */ | |
191 | static unsigned int stackleak_cleanup_execute(void) | |
192 | { | |
193 | rtx_insn *insn, *next; | |
194 | ||
195 | if (cfun->calls_alloca) | |
196 | return 0; | |
197 | ||
198 | if (large_stack_frame()) | |
199 | return 0; | |
200 | ||
201 | /* | |
202 | * Find stackleak_track_stack() calls. Loop through the chain of insns, | |
203 | * which is an RTL representation of the code for a function. | |
204 | * | |
205 | * The example of a matching insn: | |
206 | * (call_insn 8 4 10 2 (call (mem (symbol_ref ("stackleak_track_stack") | |
207 | * [flags 0x41] <function_decl 0x7f7cd3302a80 stackleak_track_stack>) | |
208 | * [0 stackleak_track_stack S1 A8]) (0)) 675 {*call} (expr_list | |
209 | * (symbol_ref ("stackleak_track_stack") [flags 0x41] <function_decl | |
210 | * 0x7f7cd3302a80 stackleak_track_stack>) (expr_list (0) (nil))) (nil)) | |
211 | */ | |
212 | for (insn = get_insns(); insn; insn = next) { | |
213 | rtx body; | |
214 | ||
215 | next = NEXT_INSN(insn); | |
216 | ||
217 | /* Check the expression code of the insn */ | |
218 | if (!CALL_P(insn)) | |
219 | continue; | |
220 | ||
221 | /* | |
222 | * Check the expression code of the insn body, which is an RTL | |
223 | * Expression (RTX) describing the side effect performed by | |
224 | * that insn. | |
225 | */ | |
226 | body = PATTERN(insn); | |
227 | ||
228 | if (GET_CODE(body) == PARALLEL) | |
229 | body = XVECEXP(body, 0, 0); | |
230 | ||
231 | if (GET_CODE(body) != CALL) | |
232 | continue; | |
233 | ||
234 | /* | |
235 | * Check the first operand of the call expression. It should | |
236 | * be a mem RTX describing the needed subroutine with a | |
237 | * symbol_ref RTX. | |
238 | */ | |
239 | body = XEXP(body, 0); | |
240 | if (GET_CODE(body) != MEM) | |
241 | continue; | |
242 | ||
243 | body = XEXP(body, 0); | |
244 | if (GET_CODE(body) != SYMBOL_REF) | |
245 | continue; | |
246 | ||
247 | if (SYMBOL_REF_DECL(body) != track_function_decl) | |
248 | continue; | |
249 | ||
250 | /* Delete the stackleak_track_stack() call */ | |
251 | delete_insn_and_edges(insn); | |
252 | #if BUILDING_GCC_VERSION >= 4007 && BUILDING_GCC_VERSION < 8000 | |
253 | if (GET_CODE(next) == NOTE && | |
254 | NOTE_KIND(next) == NOTE_INSN_CALL_ARG_LOCATION) { | |
255 | insn = next; | |
256 | next = NEXT_INSN(insn); | |
257 | delete_insn_and_edges(insn); | |
258 | } | |
259 | #endif | |
260 | } | |
261 | ||
262 | return 0; | |
263 | } | |
264 | ||
265 | static bool stackleak_gate(void) | |
266 | { | |
267 | tree section; | |
268 | ||
269 | section = lookup_attribute("section", | |
270 | DECL_ATTRIBUTES(current_function_decl)); | |
271 | if (section && TREE_VALUE(section)) { | |
272 | section = TREE_VALUE(TREE_VALUE(section)); | |
273 | ||
274 | if (!strncmp(TREE_STRING_POINTER(section), ".init.text", 10)) | |
275 | return false; | |
276 | if (!strncmp(TREE_STRING_POINTER(section), ".devinit.text", 13)) | |
277 | return false; | |
278 | if (!strncmp(TREE_STRING_POINTER(section), ".cpuinit.text", 13)) | |
279 | return false; | |
280 | if (!strncmp(TREE_STRING_POINTER(section), ".meminit.text", 13)) | |
281 | return false; | |
282 | } | |
283 | ||
284 | return track_frame_size >= 0; | |
285 | } | |
286 | ||
287 | /* Build the function declaration for stackleak_track_stack() */ | |
288 | static void stackleak_start_unit(void *gcc_data __unused, | |
289 | void *user_data __unused) | |
290 | { | |
291 | tree fntype; | |
292 | ||
293 | /* void stackleak_track_stack(void) */ | |
294 | fntype = build_function_type_list(void_type_node, NULL_TREE); | |
295 | track_function_decl = build_fn_decl(track_function, fntype); | |
296 | DECL_ASSEMBLER_NAME(track_function_decl); /* for LTO */ | |
297 | TREE_PUBLIC(track_function_decl) = 1; | |
298 | TREE_USED(track_function_decl) = 1; | |
299 | DECL_EXTERNAL(track_function_decl) = 1; | |
300 | DECL_ARTIFICIAL(track_function_decl) = 1; | |
301 | DECL_PRESERVE_P(track_function_decl) = 1; | |
302 | } | |
303 | ||
304 | /* | |
305 | * Pass gate function is a predicate function that gets executed before the | |
306 | * corresponding pass. If the return value is 'true' the pass gets executed, | |
307 | * otherwise, it is skipped. | |
308 | */ | |
309 | static bool stackleak_instrument_gate(void) | |
310 | { | |
311 | return stackleak_gate(); | |
312 | } | |
313 | ||
314 | #define PASS_NAME stackleak_instrument | |
315 | #define PROPERTIES_REQUIRED PROP_gimple_leh | PROP_cfg | |
316 | #define TODO_FLAGS_START TODO_verify_ssa | TODO_verify_flow | TODO_verify_stmts | |
317 | #define TODO_FLAGS_FINISH TODO_verify_ssa | TODO_verify_stmts | TODO_dump_func \ | |
318 | | TODO_update_ssa | TODO_rebuild_cgraph_edges | |
319 | #include "gcc-generate-gimple-pass.h" | |
320 | ||
321 | static bool stackleak_cleanup_gate(void) | |
322 | { | |
323 | return stackleak_gate(); | |
324 | } | |
325 | ||
326 | #define PASS_NAME stackleak_cleanup | |
327 | #define TODO_FLAGS_FINISH TODO_dump_func | |
328 | #include "gcc-generate-rtl-pass.h" | |
329 | ||
330 | /* | |
331 | * Every gcc plugin exports a plugin_init() function that is called right | |
332 | * after the plugin is loaded. This function is responsible for registering | |
333 | * the plugin callbacks and doing other required initialization. | |
334 | */ | |
335 | __visible int plugin_init(struct plugin_name_args *plugin_info, | |
336 | struct plugin_gcc_version *version) | |
337 | { | |
338 | const char * const plugin_name = plugin_info->base_name; | |
339 | const int argc = plugin_info->argc; | |
340 | const struct plugin_argument * const argv = plugin_info->argv; | |
341 | int i = 0; | |
342 | ||
343 | /* Extra GGC root tables describing our GTY-ed data */ | |
344 | static const struct ggc_root_tab gt_ggc_r_gt_stackleak[] = { | |
345 | { | |
346 | .base = &track_function_decl, | |
347 | .nelt = 1, | |
348 | .stride = sizeof(track_function_decl), | |
349 | .cb = >_ggc_mx_tree_node, | |
350 | .pchw = >_pch_nx_tree_node | |
351 | }, | |
352 | LAST_GGC_ROOT_TAB | |
353 | }; | |
354 | ||
355 | /* | |
356 | * The stackleak_instrument pass should be executed before the | |
357 | * "optimized" pass, which is the control flow graph cleanup that is | |
358 | * performed just before expanding gcc trees to the RTL. In former | |
359 | * versions of the plugin this new pass was inserted before the | |
360 | * "tree_profile" pass, which is currently called "profile". | |
361 | */ | |
362 | PASS_INFO(stackleak_instrument, "optimized", 1, | |
363 | PASS_POS_INSERT_BEFORE); | |
364 | ||
365 | /* | |
8fb2dfb2 AP |
366 | * The stackleak_cleanup pass should be executed before the "*free_cfg" |
367 | * pass. It's the moment when the stack frame size is already final, | |
368 | * function prologues and epilogues are generated, and the | |
369 | * machine-dependent code transformations are not done. | |
10e9ae9f | 370 | */ |
8fb2dfb2 | 371 | PASS_INFO(stackleak_cleanup, "*free_cfg", 1, PASS_POS_INSERT_BEFORE); |
10e9ae9f AP |
372 | |
373 | if (!plugin_default_version_check(version, &gcc_version)) { | |
374 | error(G_("incompatible gcc/plugin versions")); | |
375 | return 1; | |
376 | } | |
377 | ||
378 | /* Parse the plugin arguments */ | |
379 | for (i = 0; i < argc; i++) { | |
380 | if (!strcmp(argv[i].key, "disable")) | |
381 | return 0; | |
382 | ||
383 | if (!strcmp(argv[i].key, "track-min-size")) { | |
384 | if (!argv[i].value) { | |
385 | error(G_("no value supplied for option '-fplugin-arg-%s-%s'"), | |
386 | plugin_name, argv[i].key); | |
387 | return 1; | |
388 | } | |
389 | ||
390 | track_frame_size = atoi(argv[i].value); | |
391 | if (track_frame_size < 0) { | |
392 | error(G_("invalid option argument '-fplugin-arg-%s-%s=%s'"), | |
393 | plugin_name, argv[i].key, argv[i].value); | |
394 | return 1; | |
395 | } | |
396 | } else { | |
397 | error(G_("unknown option '-fplugin-arg-%s-%s'"), | |
398 | plugin_name, argv[i].key); | |
399 | return 1; | |
400 | } | |
401 | } | |
402 | ||
403 | /* Give the information about the plugin */ | |
404 | register_callback(plugin_name, PLUGIN_INFO, NULL, | |
405 | &stackleak_plugin_info); | |
406 | ||
407 | /* Register to be called before processing a translation unit */ | |
408 | register_callback(plugin_name, PLUGIN_START_UNIT, | |
409 | &stackleak_start_unit, NULL); | |
410 | ||
411 | /* Register an extra GCC garbage collector (GGC) root table */ | |
412 | register_callback(plugin_name, PLUGIN_REGISTER_GGC_ROOTS, NULL, | |
413 | (void *)>_ggc_r_gt_stackleak); | |
414 | ||
415 | /* | |
416 | * Hook into the Pass Manager to register new gcc passes. | |
417 | * | |
418 | * The stack frame size info is available only at the last RTL pass, | |
419 | * when it's too late to insert complex code like a function call. | |
420 | * So we register two gcc passes to instrument every function at first | |
421 | * and remove the unneeded instrumentation later. | |
422 | */ | |
423 | register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL, | |
424 | &stackleak_instrument_pass_info); | |
425 | register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL, | |
426 | &stackleak_cleanup_pass_info); | |
427 | ||
428 | return 0; | |
429 | } |