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AFLplusplus/src/afl-fuzz-bitmap.c
Dominik Maier 1dbefc14ea fixed bugs in custom_describe, reported by wizche
2020-12-04 14:26:48 +01:00

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/*
american fuzzy lop++ - bitmap related routines
----------------------------------------------
Originally written by Michal Zalewski
Now maintained by Marc Heuse <mh@mh-sec.de>,
Heiko Eißfeldt <heiko.eissfeldt@hexco.de> and
Andrea Fioraldi <andreafioraldi@gmail.com>
Copyright 2016, 2017 Google Inc. All rights reserved.
Copyright 2019-2020 AFLplusplus Project. All rights reserved.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at:
http://www.apache.org/licenses/LICENSE-2.0
This is the real deal: the program takes an instrumented binary and
attempts a variety of basic fuzzing tricks, paying close attention to
how they affect the execution path.
*/
#include "afl-fuzz.h"
#include <limits.h>
/* Write bitmap to file. The bitmap is useful mostly for the secret
-B option, to focus a separate fuzzing session on a particular
interesting input without rediscovering all the others. */
void write_bitmap(afl_state_t *afl) {
u8 fname[PATH_MAX];
s32 fd;
if (!afl->bitmap_changed) { return; }
afl->bitmap_changed = 0;
snprintf(fname, PATH_MAX, "%s/fuzz_bitmap", afl->out_dir);
fd = open(fname, O_WRONLY | O_CREAT | O_TRUNC, 0600);
if (fd < 0) { PFATAL("Unable to open '%s'", fname); }
ck_write(fd, afl->virgin_bits, afl->fsrv.map_size, fname);
close(fd);
}
/* Check if the current execution path brings anything new to the table.
Update virgin bits to reflect the finds. Returns 1 if the only change is
the hit-count for a particular tuple; 2 if there are new tuples seen.
Updates the map, so subsequent calls will always return 0.
This function is called after every exec() on a fairly large buffer, so
it needs to be fast. We do this in 32-bit and 64-bit flavors. */
u8 __attribute__((hot)) has_new_bits(afl_state_t *afl, u8 *virgin_map) {
#ifdef WORD_SIZE_64
u64 *current = (u64 *)afl->fsrv.trace_bits;
u64 *virgin = (u64 *)virgin_map;
u32 i = (afl->fsrv.map_size >> 3);
#else
u32 *current = (u32 *)afl->fsrv.trace_bits;
u32 *virgin = (u32 *)virgin_map;
u32 i = (afl->fsrv.map_size >> 2);
#endif /* ^WORD_SIZE_64 */
// the map size must be a minimum of 8 bytes.
// for variable/dynamic map sizes this is ensured in the forkserver
u8 ret = 0;
while (i--) {
/* Optimize for (*current & *virgin) == 0 - i.e., no bits in current bitmap
that have not been already cleared from the virgin map - since this will
almost always be the case. */
// the (*current) is unnecessary but speeds up the overall comparison
if (unlikely(*current) && unlikely(*current & *virgin)) {
if (likely(ret < 2)) {
u8 *cur = (u8 *)current;
u8 *vir = (u8 *)virgin;
/* Looks like we have not found any new bytes yet; see if any non-zero
bytes in current[] are pristine in virgin[]. */
#ifdef WORD_SIZE_64
if (*virgin == 0xffffffffffffffff || (cur[0] && vir[0] == 0xff) ||
(cur[1] && vir[1] == 0xff) || (cur[2] && vir[2] == 0xff) ||
(cur[3] && vir[3] == 0xff) || (cur[4] && vir[4] == 0xff) ||
(cur[5] && vir[5] == 0xff) || (cur[6] && vir[6] == 0xff) ||
(cur[7] && vir[7] == 0xff)) {
ret = 2;
} else {
ret = 1;
}
#else
if (*virgin == 0xffffffff || (cur[0] && vir[0] == 0xff) ||
(cur[1] && vir[1] == 0xff) || (cur[2] && vir[2] == 0xff) ||
(cur[3] && vir[3] == 0xff))
ret = 2;
else
ret = 1;
#endif /* ^WORD_SIZE_64 */
}
*virgin &= ~*current;
}
++current;
++virgin;
}
if (unlikely(ret) && likely(virgin_map == afl->virgin_bits)) {
afl->bitmap_changed = 1;
}
return ret;
}
/* Count the number of bits set in the provided bitmap. Used for the status
screen several times every second, does not have to be fast. */
u32 count_bits(afl_state_t *afl, u8 *mem) {
u32 *ptr = (u32 *)mem;
u32 i = (afl->fsrv.map_size >> 2);
u32 ret = 0;
while (i--) {
u32 v = *(ptr++);
/* This gets called on the inverse, virgin bitmap; optimize for sparse
data. */
if (v == 0xffffffff) {
ret += 32;
continue;
}
v -= ((v >> 1) & 0x55555555);
v = (v & 0x33333333) + ((v >> 2) & 0x33333333);
ret += (((v + (v >> 4)) & 0xF0F0F0F) * 0x01010101) >> 24;
}
return ret;
}
/* Count the number of bytes set in the bitmap. Called fairly sporadically,
mostly to update the status screen or calibrate and examine confirmed
new paths. */
u32 count_bytes(afl_state_t *afl, u8 *mem) {
u32 *ptr = (u32 *)mem;
u32 i = (afl->fsrv.map_size >> 2);
u32 ret = 0;
while (i--) {
u32 v = *(ptr++);
if (!v) { continue; }
if (v & 0x000000ff) { ++ret; }
if (v & 0x0000ff00) { ++ret; }
if (v & 0x00ff0000) { ++ret; }
if (v & 0xff000000) { ++ret; }
}
return ret;
}
/* Count the number of non-255 bytes set in the bitmap. Used strictly for the
status screen, several calls per second or so. */
u32 count_non_255_bytes(afl_state_t *afl, u8 *mem) {
u32 *ptr = (u32 *)mem;
u32 i = (afl->fsrv.map_size >> 2);
u32 ret = 0;
while (i--) {
u32 v = *(ptr++);
/* This is called on the virgin bitmap, so optimize for the most likely
case. */
if (v == 0xffffffff) { continue; }
if ((v & 0x000000ff) != 0x000000ff) { ++ret; }
if ((v & 0x0000ff00) != 0x0000ff00) { ++ret; }
if ((v & 0x00ff0000) != 0x00ff0000) { ++ret; }
if ((v & 0xff000000) != 0xff000000) { ++ret; }
}
return ret;
}
/* Destructively simplify trace by eliminating hit count information
and replacing it with 0x80 or 0x01 depending on whether the tuple
is hit or not. Called on every new crash or timeout, should be
reasonably fast. */
const u8 simplify_lookup[256] = {
[0] = 1, [1 ... 255] = 128
};
#ifdef WORD_SIZE_64
void simplify_trace(afl_state_t *afl, u64 *mem) {
u32 i = (afl->fsrv.map_size >> 3);
while (i--) {
/* Optimize for sparse bitmaps. */
if (unlikely(*mem)) {
u8 *mem8 = (u8 *)mem;
mem8[0] = simplify_lookup[mem8[0]];
mem8[1] = simplify_lookup[mem8[1]];
mem8[2] = simplify_lookup[mem8[2]];
mem8[3] = simplify_lookup[mem8[3]];
mem8[4] = simplify_lookup[mem8[4]];
mem8[5] = simplify_lookup[mem8[5]];
mem8[6] = simplify_lookup[mem8[6]];
mem8[7] = simplify_lookup[mem8[7]];
} else {
*mem = 0x0101010101010101ULL;
}
++mem;
}
}
#else
void simplify_trace(afl_state_t *afl, u32 *mem) {
u32 i = (afl->fsrv.map_size >> 2);
while (i--) {
/* Optimize for sparse bitmaps. */
if (unlikely(*mem)) {
u8 *mem8 = (u8 *)mem;
mem8[0] = simplify_lookup[mem8[0]];
mem8[1] = simplify_lookup[mem8[1]];
mem8[2] = simplify_lookup[mem8[2]];
mem8[3] = simplify_lookup[mem8[3]];
} else
*mem = 0x01010101;
++mem;
}
}
#endif /* ^WORD_SIZE_64 */
/* Destructively classify execution counts in a trace. This is used as a
preprocessing step for any newly acquired traces. Called on every exec,
must be fast. */
static const u8 count_class_lookup8[256] = {
[0] = 0,
[1] = 1,
[2] = 2,
[3] = 4,
[4 ... 7] = 8,
[8 ... 15] = 16,
[16 ... 31] = 32,
[32 ... 127] = 64,
[128 ... 255] = 128
};
static u16 count_class_lookup16[65536];
void init_count_class16(void) {
u32 b1, b2;
for (b1 = 0; b1 < 256; b1++) {
for (b2 = 0; b2 < 256; b2++) {
count_class_lookup16[(b1 << 8) + b2] =
(count_class_lookup8[b1] << 8) | count_class_lookup8[b2];
}
}
}
#ifdef WORD_SIZE_64
void __attribute__((hot)) classify_counts(afl_forkserver_t *fsrv) {
u64 *mem = (u64 *)fsrv->trace_bits;
u32 i = (fsrv->map_size >> 3);
while (i--) {
/* Optimize for sparse bitmaps. */
if (unlikely(*mem)) {
u16 *mem16 = (u16 *)mem;
mem16[0] = count_class_lookup16[mem16[0]];
mem16[1] = count_class_lookup16[mem16[1]];
mem16[2] = count_class_lookup16[mem16[2]];
mem16[3] = count_class_lookup16[mem16[3]];
}
++mem;
}
}
#else
void __attribute__((hot)) classify_counts(afl_forkserver_t *fsrv) {
u32 *mem = (u32 *)fsrv->trace_bits;
u32 i = (fsrv->map_size >> 2);
while (i--) {
/* Optimize for sparse bitmaps. */
if (unlikely(*mem)) {
u16 *mem16 = (u16 *)mem;
mem16[0] = count_class_lookup16[mem16[0]];
mem16[1] = count_class_lookup16[mem16[1]];
}
++mem;
}
}
#endif /* ^WORD_SIZE_64 */
/* Compact trace bytes into a smaller bitmap. We effectively just drop the
count information here. This is called only sporadically, for some
new paths. */
void minimize_bits(afl_state_t *afl, u8 *dst, u8 *src) {
u32 i = 0;
while (i < afl->fsrv.map_size) {
if (*(src++)) { dst[i >> 3] |= 1 << (i & 7); }
++i;
}
}
#ifndef SIMPLE_FILES
/* Construct a file name for a new test case, capturing the operation
that led to its discovery. Returns a ptr to afl->describe_op_buf_256. */
u8 *describe_op(afl_state_t *afl, u8 new_bits, size_t max_description_len) {
size_t real_max_len =
MIN(max_description_len, sizeof(afl->describe_op_buf_256));
u8 *ret = afl->describe_op_buf_256;
if (unlikely(afl->syncing_party)) {
sprintf(ret, "sync:%s,src:%06u", afl->syncing_party, afl->syncing_case);
} else {
sprintf(ret, "src:%06u", afl->current_entry);
if (afl->splicing_with >= 0) {
sprintf(ret + strlen(ret), "+%06d", afl->splicing_with);
}
sprintf(ret + strlen(ret), ",time:%llu", get_cur_time() - afl->start_time);
if (afl->current_custom_fuzz &&
afl->current_custom_fuzz->afl_custom_describe) {
/* We are currently in a custom mutator that supports afl_custom_describe,
* use it! */
size_t len_current = strlen(ret);
ret[len_current++] = ',';
ret[len_current] = '\0';
size_t size_left = real_max_len - len_current - strlen(",+cov") - 2;
assert(size_left > 0);
const char *custom_description =
afl->current_custom_fuzz->afl_custom_describe(
afl->current_custom_fuzz->data, size_left);
if (!custom_description || !custom_description[0]) {
DEBUGF("Error getting a description from afl_custom_describe");
/* Take the stage name as description fallback */
sprintf(ret + len_current, "op:%s", afl->stage_short);
} else {
/* We got a proper custom description, use it */
strncat(ret + len_current, custom_description, size_left);
}
} else {
/* Normal testcase descriptions start here */
sprintf(ret + strlen(ret), ",op:%s", afl->stage_short);
if (afl->stage_cur_byte >= 0) {
sprintf(ret + strlen(ret), ",pos:%d", afl->stage_cur_byte);
if (afl->stage_val_type != STAGE_VAL_NONE) {
sprintf(ret + strlen(ret), ",val:%s%+d",
(afl->stage_val_type == STAGE_VAL_BE) ? "be:" : "",
afl->stage_cur_val);
}
} else {
sprintf(ret + strlen(ret), ",rep:%d", afl->stage_cur_val);
}
}
}
if (new_bits == 2) { strcat(ret, ",+cov"); }
assert(strlen(ret) <= max_description_len);
return ret;
}
#endif /* !SIMPLE_FILES */
/* Write a message accompanying the crash directory :-) */
static void write_crash_readme(afl_state_t *afl) {
u8 fn[PATH_MAX];
s32 fd;
FILE *f;
u8 val_buf[STRINGIFY_VAL_SIZE_MAX];
sprintf(fn, "%s/crashes/README.txt", afl->out_dir);
fd = open(fn, O_WRONLY | O_CREAT | O_EXCL, 0600);
/* Do not die on errors here - that would be impolite. */
if (unlikely(fd < 0)) { return; }
f = fdopen(fd, "w");
if (unlikely(!f)) {
close(fd);
return;
}
fprintf(
f,
"Command line used to find this crash:\n\n"
"%s\n\n"
"If you can't reproduce a bug outside of afl-fuzz, be sure to set the "
"same\n"
"memory limit. The limit used for this fuzzing session was %s.\n\n"
"Need a tool to minimize test cases before investigating the crashes or "
"sending\n"
"them to a vendor? Check out the afl-tmin that comes with the fuzzer!\n\n"
"Found any cool bugs in open-source tools using afl-fuzz? If yes, please "
"drop\n"
"an mail at <afl-users@googlegroups.com> once the issues are fixed\n\n"
" https://github.com/AFLplusplus/AFLplusplus\n\n",
afl->orig_cmdline,
stringify_mem_size(val_buf, sizeof(val_buf),
afl->fsrv.mem_limit << 20)); /* ignore errors */
fclose(f);
}
/* Check if the result of an execve() during routine fuzzing is interesting,
save or queue the input test case for further analysis if so. Returns 1 if
entry is saved, 0 otherwise. */
u8 __attribute__((hot))
save_if_interesting(afl_state_t *afl, void *mem, u32 len, u8 fault) {
if (unlikely(len == 0)) { return 0; }
u8 *queue_fn = "";
u8 new_bits = '\0';
s32 fd;
u8 keeping = 0, res;
u64 cksum = 0;
u8 fn[PATH_MAX];
/* Update path frequency. */
/* Generating a hash on every input is super expensive. Bad idea and should
only be used for special schedules */
if (unlikely(afl->schedule >= FAST && afl->schedule <= RARE)) {
cksum = hash64(afl->fsrv.trace_bits, afl->fsrv.map_size, HASH_CONST);
/* Saturated increment */
if (afl->n_fuzz[cksum % N_FUZZ_SIZE] < 0xFFFFFFFF)
afl->n_fuzz[cksum % N_FUZZ_SIZE]++;
}
if (likely(fault == afl->crash_mode)) {
/* Keep only if there are new bits in the map, add to queue for
future fuzzing, etc. */
if (!(new_bits = has_new_bits(afl, afl->virgin_bits))) {
if (unlikely(afl->crash_mode)) { ++afl->total_crashes; }
return 0;
}
#ifndef SIMPLE_FILES
queue_fn = alloc_printf(
"%s/queue/id:%06u,%s", afl->out_dir, afl->queued_paths,
describe_op(afl, new_bits, NAME_MAX - strlen("id:000000,")));
#else
queue_fn =
alloc_printf("%s/queue/id_%06u", afl->out_dir, afl->queued_paths);
#endif /* ^!SIMPLE_FILES */
fd = open(queue_fn, O_WRONLY | O_CREAT | O_EXCL, 0600);
if (unlikely(fd < 0)) { PFATAL("Unable to create '%s'", queue_fn); }
ck_write(fd, mem, len, queue_fn);
close(fd);
add_to_queue(afl, queue_fn, len, 0);
#ifdef INTROSPECTION
if (afl->custom_mutators_count && afl->current_custom_fuzz) {
LIST_FOREACH(&afl->custom_mutator_list, struct custom_mutator, {
if (afl->current_custom_fuzz == el && el->afl_custom_introspection) {
const char *ptr = el->afl_custom_introspection(el->data);
if (ptr != NULL && *ptr != 0) {
fprintf(afl->introspection_file, "QUEUE CUSTOM %s = %s\n", ptr,
afl->queue_top->fname);
}
}
});
} else if (afl->mutation[0] != 0) {
fprintf(afl->introspection_file, "QUEUE %s = %s\n", afl->mutation,
afl->queue_top->fname);
}
#endif
if (new_bits == 2) {
afl->queue_top->has_new_cov = 1;
++afl->queued_with_cov;
}
if (cksum)
afl->queue_top->exec_cksum = cksum;
else
cksum = afl->queue_top->exec_cksum =
hash64(afl->fsrv.trace_bits, afl->fsrv.map_size, HASH_CONST);
if (afl->schedule >= FAST && afl->schedule <= RARE) {
afl->queue_top->n_fuzz_entry = cksum % N_FUZZ_SIZE;
afl->n_fuzz[afl->queue_top->n_fuzz_entry] = 1;
}
/* Try to calibrate inline; this also calls update_bitmap_score() when
successful. */
res = calibrate_case(afl, afl->queue_top, mem, afl->queue_cycle - 1, 0);
if (unlikely(res == FSRV_RUN_ERROR)) {
FATAL("Unable to execute target application");
}
if (likely(afl->q_testcase_max_cache_size)) {
queue_testcase_store_mem(afl, afl->queue_top, mem);
}
keeping = 1;
}
switch (fault) {
case FSRV_RUN_TMOUT:
/* Timeouts are not very interesting, but we're still obliged to keep
a handful of samples. We use the presence of new bits in the
hang-specific bitmap as a signal of uniqueness. In "non-instrumented"
mode, we just keep everything. */
++afl->total_tmouts;
if (afl->unique_hangs >= KEEP_UNIQUE_HANG) { return keeping; }
if (likely(!afl->non_instrumented_mode)) {
#ifdef WORD_SIZE_64
simplify_trace(afl, (u64 *)afl->fsrv.trace_bits);
#else
simplify_trace(afl, (u32 *)afl->fsrv.trace_bits);
#endif /* ^WORD_SIZE_64 */
if (!has_new_bits(afl, afl->virgin_tmout)) { return keeping; }
}
++afl->unique_tmouts;
#ifdef INTROSPECTION
if (afl->custom_mutators_count && afl->current_custom_fuzz) {
LIST_FOREACH(&afl->custom_mutator_list, struct custom_mutator, {
if (afl->current_custom_fuzz == el && el->afl_custom_introspection) {
const char *ptr = el->afl_custom_introspection(el->data);
if (ptr != NULL && *ptr != 0) {
fprintf(afl->introspection_file,
"UNIQUE_TIMEOUT CUSTOM %s = %s\n", ptr,
afl->queue_top->fname);
}
}
});
} else if (afl->mutation[0] != 0) {
fprintf(afl->introspection_file, "UNIQUE_TIMEOUT %s\n", afl->mutation);
}
#endif
/* Before saving, we make sure that it's a genuine hang by re-running
the target with a more generous timeout (unless the default timeout
is already generous). */
if (afl->fsrv.exec_tmout < afl->hang_tmout) {
u8 new_fault;
write_to_testcase(afl, mem, len);
new_fault = fuzz_run_target(afl, &afl->fsrv, afl->hang_tmout);
/* A corner case that one user reported bumping into: increasing the
timeout actually uncovers a crash. Make sure we don't discard it if
so. */
if (!afl->stop_soon && new_fault == FSRV_RUN_CRASH) {
goto keep_as_crash;
}
if (afl->stop_soon || new_fault != FSRV_RUN_TMOUT) { return keeping; }
}
#ifndef SIMPLE_FILES
snprintf(fn, PATH_MAX, "%s/hangs/id:%06llu,%s", afl->out_dir,
afl->unique_hangs,
describe_op(afl, 0, NAME_MAX - strlen("id:000000,")));
#else
snprintf(fn, PATH_MAX, "%s/hangs/id_%06llu", afl->out_dir,
afl->unique_hangs);
#endif /* ^!SIMPLE_FILES */
++afl->unique_hangs;
afl->last_hang_time = get_cur_time();
break;
case FSRV_RUN_CRASH:
keep_as_crash:
/* This is handled in a manner roughly similar to timeouts,
except for slightly different limits and no need to re-run test
cases. */
++afl->total_crashes;
if (afl->unique_crashes >= KEEP_UNIQUE_CRASH) { return keeping; }
if (likely(!afl->non_instrumented_mode)) {
#ifdef WORD_SIZE_64
simplify_trace(afl, (u64 *)afl->fsrv.trace_bits);
#else
simplify_trace(afl, (u32 *)afl->fsrv.trace_bits);
#endif /* ^WORD_SIZE_64 */
if (!has_new_bits(afl, afl->virgin_crash)) { return keeping; }
}
if (unlikely(!afl->unique_crashes)) { write_crash_readme(afl); }
#ifndef SIMPLE_FILES
snprintf(fn, PATH_MAX, "%s/crashes/id:%06llu,sig:%02u,%s", afl->out_dir,
afl->unique_crashes, afl->fsrv.last_kill_signal,
describe_op(afl, 0, NAME_MAX - strlen("id:000000,sig:00,")));
#else
snprintf(fn, PATH_MAX, "%s/crashes/id_%06llu_%02u", afl->out_dir,
afl->unique_crashes, afl->last_kill_signal);
#endif /* ^!SIMPLE_FILES */
++afl->unique_crashes;
#ifdef INTROSPECTION
if (afl->custom_mutators_count && afl->current_custom_fuzz) {
LIST_FOREACH(&afl->custom_mutator_list, struct custom_mutator, {
if (afl->current_custom_fuzz == el && el->afl_custom_introspection) {
const char *ptr = el->afl_custom_introspection(el->data);
if (ptr != NULL && *ptr != 0) {
fprintf(afl->introspection_file, "UNIQUE_CRASH CUSTOM %s = %s\n",
ptr, afl->queue_top->fname);
}
}
});
} else if (afl->mutation[0] != 0) {
fprintf(afl->introspection_file, "UNIQUE_CRASH %s\n", afl->mutation);
}
#endif
if (unlikely(afl->infoexec)) {
// if the user wants to be informed on new crashes - do that
#if !TARGET_OS_IPHONE
// we dont care if system errors, but we dont want a
// compiler warning either
// See
// https://stackoverflow.com/questions/11888594/ignoring-return-values-in-c
(void)(system(afl->infoexec) + 1);
#else
WARNF("command execution unsupported");
#endif
}
afl->last_crash_time = get_cur_time();
afl->last_crash_execs = afl->fsrv.total_execs;
break;
case FSRV_RUN_ERROR:
FATAL("Unable to execute target application");
default:
return keeping;
}
/* If we're here, we apparently want to save the crash or hang
test case, too. */
fd = open(fn, O_WRONLY | O_CREAT | O_EXCL, 0600);
if (unlikely(fd < 0)) { PFATAL("Unable to create '%s'", fn); }
ck_write(fd, mem, len, fn);
close(fd);
return keeping;
}
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