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/* AddressSanitizer, a fast memory error detector.
Copyright (C) 2012 Free Software Foundation, Inc.
Contributed by Kostya Serebryany <kcc@google.com>
This file is part of GCC.
GCC is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
Software Foundation; either version 3, or (at your option) any later
version.
GCC is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
for more details.
You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3. If not see
<http://www.gnu.org/licenses/>. */
#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "tree.h"
#include "tm_p.h"
#include "basic-block.h"
#include "flags.h"
#include "function.h"
#include "tree-inline.h"
#include "gimple.h"
#include "tree-iterator.h"
#include "tree-flow.h"
#include "tree-dump.h"
#include "tree-pass.h"
#include "diagnostic.h"
#include "demangle.h"
#include "langhooks.h"
#include "ggc.h"
#include "cgraph.h"
#include "gimple.h"
#include "asan.h"
#include "gimple-pretty-print.h"
#include "target.h"
/*
AddressSanitizer finds out-of-bounds and use-after-free bugs
with <2x slowdown on average.
The tool consists of two parts:
instrumentation module (this file) and a run-time library.
The instrumentation module adds a run-time check before every memory insn.
For a 8- or 16- byte load accessing address X:
ShadowAddr = (X >> 3) + Offset
ShadowValue = *(char*)ShadowAddr; // *(short*) for 16-byte access.
if (ShadowValue)
__asan_report_load8(X);
For a load of N bytes (N=1, 2 or 4) from address X:
ShadowAddr = (X >> 3) + Offset
ShadowValue = *(char*)ShadowAddr;
if (ShadowValue)
if ((X & 7) + N - 1 > ShadowValue)
__asan_report_loadN(X);
Stores are instrumented similarly, but using __asan_report_storeN functions.
A call too __asan_init() is inserted to the list of module CTORs.
The run-time library redefines malloc (so that redzone are inserted around
the allocated memory) and free (so that reuse of free-ed memory is delayed),
provides __asan_report* and __asan_init functions.
Read more:
http://code.google.com/p/address-sanitizer/wiki/AddressSanitizerAlgorithm
Future work:
The current implementation supports only detection of out-of-bounds and
use-after-free bugs in heap.
In order to support out-of-bounds for stack and globals we will need
to create redzones for stack and global object and poison them.
*/
/* Construct a function tree for __asan_report_{load,store}{1,2,4,8,16}.
IS_STORE is either 1 (for a store) or 0 (for a load).
SIZE_IN_BYTES is one of 1, 2, 4, 8, 16. */
static tree
report_error_func (int is_store, int size_in_bytes)
{
tree fn_type;
tree def;
char name[100];
sprintf (name, "__asan_report_%s%d\n",
is_store ? "store" : "load", size_in_bytes);
fn_type = build_function_type_list (void_type_node, ptr_type_node, NULL_TREE);
def = build_fn_decl (name, fn_type);
TREE_NOTHROW (def) = 1;
TREE_THIS_VOLATILE (def) = 1; /* Attribute noreturn. Surprise! */
DECL_ATTRIBUTES (def) = tree_cons (get_identifier ("leaf"),
NULL, DECL_ATTRIBUTES (def));
DECL_ASSEMBLER_NAME (def);
return def;
}
/* Construct a function tree for __asan_init(). */
static tree
asan_init_func (void)
{
tree fn_type;
tree def;
fn_type = build_function_type_list (void_type_node, NULL_TREE);
def = build_fn_decl ("__asan_init", fn_type);
TREE_NOTHROW (def) = 1;
DECL_ASSEMBLER_NAME (def);
return def;
}
/* Instrument the memory access instruction BASE.
Insert new statements before ITER.
LOCATION is source code location.
IS_STORE is either 1 (for a store) or 0 (for a load).
SIZE_IN_BYTES is one of 1, 2, 4, 8, 16. */
static void
build_check_stmt (tree base,
gimple_stmt_iterator *iter,
location_t location, int is_store, int size_in_bytes)
{
gimple_stmt_iterator gsi;
basic_block cond_bb, then_bb, join_bb;
edge e;
tree cond, t, u;
tree base_addr;
tree shadow_value;
gimple g;
gimple_seq seq, stmts;
tree shadow_type = size_in_bytes == 16 ?
short_integer_type_node : char_type_node;
tree shadow_ptr_type = build_pointer_type (shadow_type);
tree uintptr_type = lang_hooks.types.type_for_mode (ptr_mode,
/*unsignedp=*/true);
/* We first need to split the current basic block, and start altering
the CFG. This allows us to insert the statements we're about to
construct into the right basic blocks. */
cond_bb = gimple_bb (gsi_stmt (*iter));
gsi = *iter;
gsi_prev (&gsi);
if (!gsi_end_p (gsi))
e = split_block (cond_bb, gsi_stmt (gsi));
else
e = split_block_after_labels (cond_bb);
cond_bb = e->src;
join_bb = e->dest;
/* A recap at this point: join_bb is the basic block at whose head
is the gimple statement for which this check expression is being
built. cond_bb is the (possibly new, synthetic) basic block the
end of which will contain the cache-lookup code, and a
conditional that jumps to the cache-miss code or, much more
likely, over to join_bb. */
/* Create the bb that contains the crash block. */
then_bb = create_empty_bb (cond_bb);
make_edge (cond_bb, then_bb, EDGE_TRUE_VALUE);
make_single_succ_edge (then_bb, join_bb, EDGE_FALLTHRU);
/* Mark the pseudo-fallthrough edge from cond_bb to join_bb. */
e = find_edge (cond_bb, join_bb);
e->flags = EDGE_FALSE_VALUE;
e->count = cond_bb->count;
e->probability = REG_BR_PROB_BASE;
/* Update dominance info. Note that bb_join's data was
updated by split_block. */
if (dom_info_available_p (CDI_DOMINATORS))
{
set_immediate_dominator (CDI_DOMINATORS, then_bb, cond_bb);
set_immediate_dominator (CDI_DOMINATORS, join_bb, cond_bb);
}
base_addr = create_tmp_reg (uintptr_type, "__asan_base_addr");
seq = NULL;
t = fold_convert_loc (location, uintptr_type,
unshare_expr (base));
t = force_gimple_operand (t, &stmts, false, NULL_TREE);
gimple_seq_add_seq (&seq, stmts);
g = gimple_build_assign (base_addr, t);
gimple_set_location (g, location);
gimple_seq_add_stmt (&seq, g);
/* Build
(base_addr >> ASAN_SHADOW_SHIFT) | targetm.asan_shadow_offset (). */
t = build2 (RSHIFT_EXPR, uintptr_type, base_addr,
build_int_cst (uintptr_type, ASAN_SHADOW_SHIFT));
t = build2 (PLUS_EXPR, uintptr_type, t,
build_int_cst (uintptr_type, targetm.asan_shadow_offset ()));
t = build1 (INDIRECT_REF, shadow_type,
build1 (VIEW_CONVERT_EXPR, shadow_ptr_type, t));
t = force_gimple_operand (t, &stmts, false, NULL_TREE);
gimple_seq_add_seq (&seq, stmts);
shadow_value = create_tmp_reg (shadow_type, "__asan_shadow");
g = gimple_build_assign (shadow_value, t);
gimple_set_location (g, location);
gimple_seq_add_stmt (&seq, g);
t = build2 (NE_EXPR, boolean_type_node, shadow_value,
build_int_cst (shadow_type, 0));
if (size_in_bytes < 8)
{
/* Slow path for 1-, 2- and 4- byte accesses.
Build ((base_addr & 7) + (size_in_bytes - 1)) >= shadow_value. */
u = build2 (BIT_AND_EXPR, uintptr_type,
base_addr,
build_int_cst (uintptr_type, 7));
u = build1 (CONVERT_EXPR, shadow_type, u);
u = build2 (PLUS_EXPR, shadow_type, u,
build_int_cst (shadow_type, size_in_bytes - 1));
u = build2 (GE_EXPR, uintptr_type, u, shadow_value);
}
else
u = build_int_cst (boolean_type_node, 1);
t = build2 (TRUTH_AND_EXPR, boolean_type_node, t, u);
t = force_gimple_operand (t, &stmts, false, NULL_TREE);
gimple_seq_add_seq (&seq, stmts);
cond = create_tmp_reg (boolean_type_node, "__asan_crash_cond");
g = gimple_build_assign (cond, t);
gimple_set_location (g, location);
gimple_seq_add_stmt (&seq, g);
g = gimple_build_cond (NE_EXPR, cond, boolean_false_node, NULL_TREE,
NULL_TREE);
gimple_set_location (g, location);
gimple_seq_add_stmt (&seq, g);
/* Generate call to the run-time library (e.g. __asan_report_load8). */
gsi = gsi_last_bb (cond_bb);
gsi_insert_seq_after (&gsi, seq, GSI_CONTINUE_LINKING);
seq = NULL;
g = gimple_build_call (report_error_func (is_store, size_in_bytes),
1, base_addr);
gimple_seq_add_stmt (&seq, g);
/* Insert the check code in the THEN block. */
gsi = gsi_start_bb (then_bb);
gsi_insert_seq_after (&gsi, seq, GSI_CONTINUE_LINKING);
*iter = gsi_start_bb (join_bb);
}
/* If T represents a memory access, add instrumentation code before ITER.
LOCATION is source code location.
IS_STORE is either 1 (for a store) or 0 (for a load). */
static void
instrument_derefs (gimple_stmt_iterator *iter, tree t,
location_t location, int is_store)
{
tree type, base;
int size_in_bytes;
type = TREE_TYPE (t);
if (type == error_mark_node)
return;
switch (TREE_CODE (t))
{
case ARRAY_REF:
case COMPONENT_REF:
case INDIRECT_REF:
case MEM_REF:
break;
default:
return;
}
size_in_bytes = tree_low_cst (TYPE_SIZE (type), 0) / BITS_PER_UNIT;
if (size_in_bytes != 1 && size_in_bytes != 2 &&
size_in_bytes != 4 && size_in_bytes != 8 && size_in_bytes != 16)
return;
{
/* For now just avoid instrumenting bit field acceses.
Fixing it is doable, but expected to be messy. */
HOST_WIDE_INT bitsize, bitpos;
tree offset;
enum machine_mode mode;
int volatilep = 0, unsignedp = 0;
get_inner_reference (t, &bitsize, &bitpos, &offset,
&mode, &unsignedp, &volatilep, false);
if (bitpos != 0 || bitsize != size_in_bytes * BITS_PER_UNIT)
return;
}
base = build_addr (t, current_function_decl);
build_check_stmt (base, iter, location, is_store, size_in_bytes);
}
/* asan: this looks too complex. Can this be done simpler? */
/* Transform
1) Memory references.
2) BUILTIN_ALLOCA calls.
*/
static void
transform_statements (void)
{
basic_block bb;
gimple_stmt_iterator i;
int saved_last_basic_block = last_basic_block;
enum gimple_rhs_class grhs_class;
FOR_EACH_BB (bb)
{
if (bb->index >= saved_last_basic_block) continue;
for (i = gsi_start_bb (bb); !gsi_end_p (i); gsi_next (&i))
{
gimple s = gsi_stmt (i);
if (gimple_code (s) != GIMPLE_ASSIGN)
continue;
instrument_derefs (&i, gimple_assign_lhs (s),
gimple_location (s), 1);
instrument_derefs (&i, gimple_assign_rhs1 (s),
gimple_location (s), 0);
grhs_class = get_gimple_rhs_class (gimple_assign_rhs_code (s));
if (grhs_class == GIMPLE_BINARY_RHS)
instrument_derefs (&i, gimple_assign_rhs2 (s),
gimple_location (s), 0);
}
}
}
/* Module-level instrumentation.
- Insert __asan_init() into the list of CTORs.
- TODO: insert redzones around globals.
*/
void
asan_finish_file (void)
{
tree ctor_statements = NULL_TREE;
append_to_statement_list (build_call_expr (asan_init_func (), 0),
&ctor_statements);
cgraph_build_static_cdtor ('I', ctor_statements,
MAX_RESERVED_INIT_PRIORITY - 1);
}
/* Instrument the current function. */
static unsigned int
asan_instrument (void)
{
struct gimplify_ctx gctx;
push_gimplify_context (&gctx);
transform_statements ();
pop_gimplify_context (NULL);
return 0;
}
static bool
gate_asan (void)
{
return flag_asan != 0;
}
struct gimple_opt_pass pass_asan =
{
{
GIMPLE_PASS,
"asan", /* name */
OPTGROUP_NONE, /* optinfo_flags */
gate_asan, /* gate */
asan_instrument, /* execute */
NULL, /* sub */
NULL, /* next */
0, /* static_pass_number */
TV_NONE, /* tv_id */
PROP_ssa | PROP_cfg | PROP_gimple_leh,/* properties_required */
0, /* properties_provided */
0, /* properties_destroyed */
0, /* todo_flags_start */
TODO_verify_flow | TODO_verify_stmts
| TODO_update_ssa /* todo_flags_finish */
}
};
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