// 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();}

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