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/*
* 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;
int frequency;
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);
frequency = compute_call_stmt_bb_frequency(current_function_decl, bb);
cgraph_create_edge(cgraph_get_node(current_function_decl), node,
stackleak_track_stack, bb->count, frequency);
}
static bool is_alloca(gimple stmt)
{
if (gimple_call_builtin_p(stmt, BUILT_IN_ALLOCA))
return true;
#if BUILDING_GCC_VERSION >= 4007
if (gimple_call_builtin_p(stmt, BUILT_IN_ALLOCA_WITH_ALIGN))
return true;
#endif
return false;
}
/*
* 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;
/*
* 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;
/* Insert stackleak_track_stack() call after alloca() */
stackleak_add_track_stack(&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);
stackleak_add_track_stack(&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
}
/*
* 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)
{
rtx_insn *insn, *next;
if (cfun->calls_alloca)
return 0;
if (large_stack_frame())
return 0;
/*
* 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 >= 4007 && 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
}
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;
}
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, "disable"))
return 0;
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 {
error(G_("unknown option '-fplugin-arg-%s-%s'"),
plugin_name, argv[i].key);
return 1;
}
}
/* 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;
}
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