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stackleak_plugin.c
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// SPDX-License-Identifier: GPL-2.0-only /* * Copyright 2011-2017 by the PaX Team <pageexec@freemail.hu> * Modified by Alexander Popov <alex.popov@linux.com> * * Note: the choice of the license means that the compilation process is * NOT 'eligible' as defined by gcc's library exception to the GPL v3, * but for the kernel it doesn't matter since it doesn't link against * any of the gcc libraries * * This gcc plugin is needed for tracking the lowest border of the kernel stack. * It instruments the kernel code inserting stackleak_track_stack() calls: * - after alloca(); * - for the functions with a stack frame size greater than or equal * to the "track-min-size" plugin parameter. * * This plugin is ported from grsecurity/PaX. For more information see: * https://grsecurity.net/ * https://pax.grsecurity.net/ * * Debugging: * - use fprintf() to stderr, debug_generic_expr(), debug_gimple_stmt(), * print_rtl_single() and debug_rtx(); * - add "-fdump-tree-all -fdump-rtl-all" to the plugin CFLAGS in * Makefile.gcc-plugins to see the verbose dumps of the gcc passes; * - use gcc -E to understand the preprocessing shenanigans; * - use gcc with enabled CFG/GIMPLE/SSA verification (--enable-checking). */ #include "gcc-common.h" __visible int plugin_is_GPL_compatible; static int track_frame_size = -1; static bool build_for_x86 = false; static const char track_function[] = "stackleak_track_stack"; static bool disable = false; static bool verbose = false; /* * Mark these global variables (roots) for gcc garbage collector since * they point to the garbage-collected memory. */ static GTY(()) tree track_function_decl; static struct plugin_info stackleak_plugin_info = { .version = PLUGIN_VERSION, .help = "track-min-size=nn\ttrack stack for functions with a stack frame size >= nn bytes\n" "arch=target_arch\tspecify target build arch\n" "disable\t\tdo not activate the plugin\n" "verbose\t\tprint info about the instrumentation\n" }; static void add_stack_tracking_gcall(gimple_stmt_iterator *gsi, bool after) { gimple stmt; gcall *gimple_call; cgraph_node_ptr node; basic_block bb; /* Insert calling stackleak_track_stack() */ stmt = gimple_build_call(track_function_decl, 0); gimple_call = as_a_gcall(stmt); if (after) gsi_insert_after(gsi, gimple_call, GSI_CONTINUE_LINKING); else gsi_insert_before(gsi, gimple_call, GSI_SAME_STMT); /* Update the cgraph */ bb = gimple_bb(gimple_call); node = cgraph_get_create_node(track_function_decl); gcc_assert(node); cgraph_create_edge(cgraph_get_node(current_function_decl), node, gimple_call, bb->count, compute_call_stmt_bb_frequency(current_function_decl, bb)); } static bool is_alloca(gimple stmt) { if (gimple_call_builtin_p(stmt, BUILT_IN_ALLOCA)) return true; if (gimple_call_builtin_p(stmt, BUILT_IN_ALLOCA_WITH_ALIGN)) return true; return false; } static tree get_current_stack_pointer_decl(void) { varpool_node_ptr node; FOR_EACH_VARIABLE(node) { tree var = NODE_DECL(node); tree name = DECL_NAME(var); if (DECL_NAME_LENGTH(var) != sizeof("current_stack_pointer") - 1) continue; if (strcmp(IDENTIFIER_POINTER(name), "current_stack_pointer")) continue; return var; } if (verbose) { fprintf(stderr, "stackleak: missing current_stack_pointer in %s()\n", DECL_NAME_POINTER(current_function_decl)); } return NULL_TREE; } static void add_stack_tracking_gasm(gimple_stmt_iterator *gsi, bool after) { gasm *asm_call = NULL; tree sp_decl, input; vec<tree, va_gc> *inputs = NULL; /* 'no_caller_saved_registers' is currently supported only for x86 */ gcc_assert(build_for_x86); /* * Insert calling stackleak_track_stack() in asm: * asm volatile("call stackleak_track_stack" * :: "r" (current_stack_pointer)) * Use ASM_CALL_CONSTRAINT trick from arch/x86/include/asm/asm.h. * This constraint is taken into account during gcc shrink-wrapping * optimization. It is needed to be sure that stackleak_track_stack() * call is inserted after the prologue of the containing function, * when the stack frame is prepared. */ sp_decl = get_current_stack_pointer_decl(); if (sp_decl == NULL_TREE) { add_stack_tracking_gcall(gsi, after); return; } input = build_tree_list(NULL_TREE, build_const_char_string(2, "r")); input = chainon(NULL_TREE, build_tree_list(input, sp_decl)); vec_safe_push(inputs, input); asm_call = gimple_build_asm_vec("call stackleak_track_stack", inputs, NULL, NULL, NULL); gimple_asm_set_volatile(asm_call, true); if (after) gsi_insert_after(gsi, asm_call, GSI_CONTINUE_LINKING); else gsi_insert_before(gsi, asm_call, GSI_SAME_STMT); update_stmt(asm_call); } static void add_stack_tracking(gimple_stmt_iterator *gsi, bool after) { /* * The 'no_caller_saved_registers' attribute is used for * stackleak_track_stack(). If the compiler supports this attribute for * the target arch, we can add calling stackleak_track_stack() in asm. * That improves performance: we avoid useless operations with the * caller-saved registers in the functions from which we will remove * stackleak_track_stack() call during the stackleak_cleanup pass. */ if (lookup_attribute_spec(get_identifier("no_caller_saved_registers"))) add_stack_tracking_gasm(gsi, after); else add_stack_tracking_gcall(gsi, after); } /* * Work with the GIMPLE representation of the code. Insert the * stackleak_track_stack() call after alloca() and into the beginning * of the function if it is not instrumented. */ static unsigned int stackleak_instrument_execute(void) { basic_block bb, entry_bb; bool prologue_instrumented = false, is_leaf = true; gimple_stmt_iterator gsi = { 0 }; /* * ENTRY_BLOCK_PTR is a basic block which represents possible entry * point of a function. This block does not contain any code and * has a CFG edge to its successor. */ gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun))); entry_bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun)); /* * Loop through the GIMPLE statements in each of cfun basic blocks. * cfun is a global variable which represents the function that is * currently processed. */ FOR_EACH_BB_FN(bb, cfun) { for (gsi = gsi_start_bb(bb); !gsi_end_p(gsi); gsi_next(&gsi)) { gimple stmt; stmt = gsi_stmt(gsi); /* Leaf function is a function which makes no calls */ if (is_gimple_call(stmt)) is_leaf = false; if (!is_alloca(stmt)) continue; if (verbose) { fprintf(stderr, "stackleak: be careful, alloca() in %s()\n", DECL_NAME_POINTER(current_function_decl)); } /* Insert stackleak_track_stack() call after alloca() */ add_stack_tracking(&gsi, true); if (bb == entry_bb) prologue_instrumented = true; } } if (prologue_instrumented) return 0; /* * Special cases to skip the instrumentation. * * Taking the address of static inline functions materializes them, * but we mustn't instrument some of them as the resulting stack * alignment required by the function call ABI will break other * assumptions regarding the expected (but not otherwise enforced) * register clobbering ABI. * * Case in point: native_save_fl on amd64 when optimized for size * clobbers rdx if it were instrumented here. * * TODO: any more special cases? */ if (is_leaf && !TREE_PUBLIC(current_function_decl) && DECL_DECLARED_INLINE_P(current_function_decl)) { return 0; } if (is_leaf && !strncmp(IDENTIFIER_POINTER(DECL_NAME(current_function_decl)), "_paravirt_", 10)) { return 0; } /* Insert stackleak_track_stack() call at the function beginning */ bb = entry_bb; if (!single_pred_p(bb)) { /* gcc_assert(bb_loop_depth(bb) || (bb->flags & BB_IRREDUCIBLE_LOOP)); */ split_edge(single_succ_edge(ENTRY_BLOCK_PTR_FOR_FN(cfun))); gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun))); bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun)); } gsi = gsi_after_labels(bb); add_stack_tracking(&gsi, false); return 0; } static bool large_stack_frame(void) { #if BUILDING_GCC_VERSION >= 8000 return maybe_ge(get_frame_size(), track_frame_size); #else return (get_frame_size() >= track_frame_size); #endif } static void remove_stack_tracking_gcall(void) { rtx_insn *insn, *next; /* * Find stackleak_track_stack() calls. Loop through the chain of insns, * which is an RTL representation of the code for a function. * * The example of a matching insn: * (call_insn 8 4 10 2 (call (mem (symbol_ref ("stackleak_track_stack") * [flags 0x41] <function_decl 0x7f7cd3302a80 stackleak_track_stack>) * [0 stackleak_track_stack S1 A8]) (0)) 675 {*call} (expr_list * (symbol_ref ("stackleak_track_stack") [flags 0x41] <function_decl * 0x7f7cd3302a80 stackleak_track_stack>) (expr_list (0) (nil))) (nil)) */ for (insn = get_insns(); insn; insn = next) { rtx body; next = NEXT_INSN(insn); /* Check the expression code of the insn */ if (!CALL_P(insn)) continue; /* * Check the expression code of the insn body, which is an RTL * Expression (RTX) describing the side effect performed by * that insn. */ body = PATTERN(insn); if (GET_CODE(body) == PARALLEL) body = XVECEXP(body, 0, 0); if (GET_CODE(body) != CALL) continue; /* * Check the first operand of the call expression. It should * be a mem RTX describing the needed subroutine with a * symbol_ref RTX. */ body = XEXP(body, 0); if (GET_CODE(body) != MEM) continue; body = XEXP(body, 0); if (GET_CODE(body) != SYMBOL_REF) continue; if (SYMBOL_REF_DECL(body) != track_function_decl) continue; /* Delete the stackleak_track_stack() call */ delete_insn_and_edges(insn); #if BUILDING_GCC_VERSION < 8000 if (GET_CODE(next) == NOTE && NOTE_KIND(next) == NOTE_INSN_CALL_ARG_LOCATION) { insn = next; next = NEXT_INSN(insn); delete_insn_and_edges(insn); } #endif } } static bool remove_stack_tracking_gasm(void) { bool removed = false; rtx_insn *insn, *next; /* 'no_caller_saved_registers' is currently supported only for x86 */ gcc_assert(build_for_x86); /* * Find stackleak_track_stack() asm calls. Loop through the chain of * insns, which is an RTL representation of the code for a function. * * The example of a matching insn: * (insn 11 5 12 2 (parallel [ (asm_operands/v * ("call stackleak_track_stack") ("") 0 * [ (reg/v:DI 7 sp [ current_stack_pointer ]) ] * [ (asm_input:DI ("r")) ] []) * (clobber (reg:CC 17 flags)) ]) -1 (nil)) */ for (insn = get_insns(); insn; insn = next) { rtx body; next = NEXT_INSN(insn); /* Check the expression code of the insn */ if (!NONJUMP_INSN_P(insn)) continue; /* * Check the expression code of the insn body, which is an RTL * Expression (RTX) describing the side effect performed by * that insn. */ body = PATTERN(insn); if (GET_CODE(body) != PARALLEL) continue; body = XVECEXP(body, 0, 0); if (GET_CODE(body) != ASM_OPERANDS) continue; if (strcmp(ASM_OPERANDS_TEMPLATE(body), "call stackleak_track_stack")) { continue; } delete_insn_and_edges(insn); gcc_assert(!removed); removed = true; } return removed; } /* * Work with the RTL representation of the code. * Remove the unneeded stackleak_track_stack() calls from the functions * which don't call alloca() and don't have a large enough stack frame size. */ static unsigned int stackleak_cleanup_execute(void) { const char *fn = DECL_NAME_POINTER(current_function_decl); bool removed = false; /* * Leave stack tracking in functions that call alloca(). * Additional case: * gcc before version 7 called allocate_dynamic_stack_space() from * expand_stack_vars() for runtime alignment of constant-sized stack * variables. That caused cfun->calls_alloca to be set for functions * that in fact don't use alloca(). * For more info see gcc commit 7072df0aae0c59ae437e. * Let's leave such functions instrumented as well. */ if (cfun->calls_alloca) { if (verbose) fprintf(stderr, "stackleak: instrument %s(): calls_alloca\n", fn); return 0; } /* Leave stack tracking in functions with large stack frame */ if (large_stack_frame()) { if (verbose) fprintf(stderr, "stackleak: instrument %s()\n", fn); return 0; } if (lookup_attribute_spec(get_identifier("no_caller_saved_registers"))) removed = remove_stack_tracking_gasm(); if (!removed) remove_stack_tracking_gcall(); return 0; } /* * STRING_CST may or may not be NUL terminated: * https://gcc.gnu.org/onlinedocs/gccint/Constant-expressions.html */ static inline bool string_equal(tree node, const char *string, int length) { if (TREE_STRING_LENGTH(node) < length) return false; if (TREE_STRING_LENGTH(node) > length + 1) return false; if (TREE_STRING_LENGTH(node) == length + 1 && TREE_STRING_POINTER(node)[length] != '\0') return false; return !memcmp(TREE_STRING_POINTER(node), string, length); } #define STRING_EQUAL(node, str) string_equal(node, str, strlen(str)) static bool stackleak_gate(void) { tree section; section = lookup_attribute("section", DECL_ATTRIBUTES(current_function_decl)); if (section && TREE_VALUE(section)) { section = TREE_VALUE(TREE_VALUE(section)); if (STRING_EQUAL(section, ".init.text")) return false; if (STRING_EQUAL(section, ".devinit.text")) return false; if (STRING_EQUAL(section, ".cpuinit.text")) return false; if (STRING_EQUAL(section, ".meminit.text")) return false; if (STRING_EQUAL(section, ".noinstr.text")) return false; if (STRING_EQUAL(section, ".entry.text")) return false; if (STRING_EQUAL(section, ".head.text")) return false; } return track_frame_size >= 0; } /* Build the function declaration for stackleak_track_stack() */ static void stackleak_start_unit(void *gcc_data __unused, void *user_data __unused) { tree fntype; /* void stackleak_track_stack(void) */ fntype = build_function_type_list(void_type_node, NULL_TREE); track_function_decl = build_fn_decl(track_function, fntype); DECL_ASSEMBLER_NAME(track_function_decl); /* for LTO */ TREE_PUBLIC(track_function_decl) = 1; TREE_USED(track_function_decl) = 1; DECL_EXTERNAL(track_function_decl) = 1; DECL_ARTIFICIAL(track_function_decl) = 1; DECL_PRESERVE_P(track_function_decl) = 1; } /* * Pass gate function is a predicate function that gets executed before the * corresponding pass. If the return value is 'true' the pass gets executed, * otherwise, it is skipped. */ static bool stackleak_instrument_gate(void) { return stackleak_gate(); } #define PASS_NAME stackleak_instrument #define PROPERTIES_REQUIRED PROP_gimple_leh | PROP_cfg #define TODO_FLAGS_START TODO_verify_ssa | TODO_verify_flow | TODO_verify_stmts #define TODO_FLAGS_FINISH TODO_verify_ssa | TODO_verify_stmts | TODO_dump_func \ | TODO_update_ssa | TODO_rebuild_cgraph_edges #include "gcc-generate-gimple-pass.h" static bool stackleak_cleanup_gate(void) { return stackleak_gate(); } #define PASS_NAME stackleak_cleanup #define TODO_FLAGS_FINISH TODO_dump_func #include "gcc-generate-rtl-pass.h" /* * Every gcc plugin exports a plugin_init() function that is called right * after the plugin is loaded. This function is responsible for registering * the plugin callbacks and doing other required initialization. */ __visible int plugin_init(struct plugin_name_args *plugin_info, struct plugin_gcc_version *version) { const char * const plugin_name = plugin_info->base_name; const int argc = plugin_info->argc; const struct plugin_argument * const argv = plugin_info->argv; int i = 0; /* Extra GGC root tables describing our GTY-ed data */ static const struct ggc_root_tab gt_ggc_r_gt_stackleak[] = { { .base = &track_function_decl, .nelt = 1, .stride = sizeof(track_function_decl), .cb = >_ggc_mx_tree_node, .pchw = >_pch_nx_tree_node }, LAST_GGC_ROOT_TAB }; /* * The stackleak_instrument pass should be executed before the * "optimized" pass, which is the control flow graph cleanup that is * performed just before expanding gcc trees to the RTL. In former * versions of the plugin this new pass was inserted before the * "tree_profile" pass, which is currently called "profile". */ PASS_INFO(stackleak_instrument, "optimized", 1, PASS_POS_INSERT_BEFORE); /* * The stackleak_cleanup pass should be executed before the "*free_cfg" * pass. It's the moment when the stack frame size is already final, * function prologues and epilogues are generated, and the * machine-dependent code transformations are not done. */ PASS_INFO(stackleak_cleanup, "*free_cfg", 1, PASS_POS_INSERT_BEFORE); if (!plugin_default_version_check(version, &gcc_version)) { error(G_("incompatible gcc/plugin versions")); return 1; } /* Parse the plugin arguments */ for (i = 0; i < argc; i++) { if (!strcmp(argv[i].key, "track-min-size")) { if (!argv[i].value) { error(G_("no value supplied for option '-fplugin-arg-%s-%s'"), plugin_name, argv[i].key); return 1; } track_frame_size = atoi(argv[i].value); if (track_frame_size < 0) { error(G_("invalid option argument '-fplugin-arg-%s-%s=%s'"), plugin_name, argv[i].key, argv[i].value); return 1; } } else if (!strcmp(argv[i].key, "arch")) { if (!argv[i].value) { error(G_("no value supplied for option '-fplugin-arg-%s-%s'"), plugin_name, argv[i].key); return 1; } if (!strcmp(argv[i].value, "x86")) build_for_x86 = true; } else if (!strcmp(argv[i].key, "disable")) { disable = true; } else if (!strcmp(argv[i].key, "verbose")) { verbose = true; } else { error(G_("unknown option '-fplugin-arg-%s-%s'"), plugin_name, argv[i].key); return 1; } } if (disable) { if (verbose) fprintf(stderr, "stackleak: disabled for this translation unit\n"); return 0; } /* Give the information about the plugin */ register_callback(plugin_name, PLUGIN_INFO, NULL, &stackleak_plugin_info); /* Register to be called before processing a translation unit */ register_callback(plugin_name, PLUGIN_START_UNIT, &stackleak_start_unit, NULL); /* Register an extra GCC garbage collector (GGC) root table */ register_callback(plugin_name, PLUGIN_REGISTER_GGC_ROOTS, NULL, (void *)>_ggc_r_gt_stackleak); /* * Hook into the Pass Manager to register new gcc passes. * * The stack frame size info is available only at the last RTL pass, * when it's too late to insert complex code like a function call. * So we register two gcc passes to instrument every function at first * and remove the unneeded instrumentation later. */ register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL, &stackleak_instrument_pass_info); register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL, &stackleak_cleanup_pass_info); return 0; }