diff options
Diffstat (limited to '')
| -rw-r--r-- | scripts/gcc-plugins/stackleak_plugin.c | 633 |
1 files changed, 633 insertions, 0 deletions
diff --git a/scripts/gcc-plugins/stackleak_plugin.c b/scripts/gcc-plugins/stackleak_plugin.c new file mode 100644 index 000000000..c5c2ce113 --- /dev/null +++ b/scripts/gcc-plugins/stackleak_plugin.c @@ -0,0 +1,633 @@ +// 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; + } + + 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; +} |