stackleak_plugin.c

/*
 * Copyright 2011-2017 by the PaX Team <pageexec@freemail.hu>
 * Modified by Alexander Popov <alex.popov@linux.com>
 * Licensed under the GPL v2
 *
 * 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() and print_simple_rtl();
 *  - 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 const char track_function[] = "stackleak_track_stack";

/*
 * 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 = "201707101337",
	.help = "track-min-size=nn\ttrack stack for functions with a stack frame size >= nn bytes\n"
		"disable\t\tdo not activate the plugin\n"
};

static void stackleak_add_track_stack(gimple_stmt_iterator *gsi, bool after)
{
	gimple stmt;
	gcall *stackleak_track_stack;
	cgraph_node_ptr node;
	basic_block bb;

	/* Insert call to void stackleak_track_stack(void) */
	stmt = gimple_build_call(track_function_decl, 0);
	stackleak_track_stack = as_a_gcall(stmt);
	if (after) {
		gsi_insert_after(gsi, stackleak_track_stack,
						GSI_CONTINUE_LINKING);
	} else {
		gsi_insert_before(gsi, stackleak_track_stack, GSI_SAME_STMT);
	}

	/* Update the cgraph */
	bb = gimple_bb(stackleak_track_stack);
	node = cgraph_get_create_node(track_function_decl);
	gcc_assert(node);
	cgraph_create_edge(cgraph_get_node(current_function_decl), node,