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fuzz: remove fork-fuzzing scaffolding

Browse Source 
Fork-fuzzing provides a few pros, but our implementation prevents us
from using fuzzers other than libFuzzer, and may be causing issues such
as coverage-failure builds on OSS-Fuzz. It is not a great long-term
solution as it depends on internal implementation details of libFuzzer
(which is no longer in active development). Remove it in favor of other
methods of resetting state between inputs.

Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
This commit is contained in:
Alexander Bulekov 2023-02-04 23:29:50 -05:00
parent f031c95941
commit d2e6f9272d
5 changed files with 3 additions and 127 deletions
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4
meson.build
View File

@ -215,10 +215,6 @@ endif
# Specify linker-script with add_project_link_arguments so that it is not placed
# within a linker --start-group/--end-group pair
if get_option('fuzzing')
add_project_link_arguments(['-Wl,-T,',
(meson.current_source_dir() / 'tests/qtest/fuzz/fork_fuzz.ld')],
native: false, language: all_languages)
# Specify a filter to only instrument code that is directly related to
# virtual-devices.
configure_file(output: 'instrumentation-filter',

41
tests/qtest/fuzz/fork_fuzz.c
View File

@ -1,41 +0,0 @@
/*
* Fork-based fuzzing helpers
*
* Copyright Red Hat Inc., 2019
*
* Authors:
* Alexander Bulekov <alxndr@bu.edu>
*
* This work is licensed under the terms of the GNU GPL, version 2 or later.
* See the COPYING file in the top-level directory.
*
*/
#include "qemu/osdep.h"
#include "fork_fuzz.h"
void counter_shm_init(void)
{
/* Copy what's in the counter region to a temporary buffer.. */
void *copy = malloc(&__FUZZ_COUNTERS_END - &__FUZZ_COUNTERS_START);
memcpy(copy,
&__FUZZ_COUNTERS_START,
&__FUZZ_COUNTERS_END - &__FUZZ_COUNTERS_START);
/* Map a shared region over the counter region */
if (mmap(&__FUZZ_COUNTERS_START,
&__FUZZ_COUNTERS_END - &__FUZZ_COUNTERS_START,
PROT_READ | PROT_WRITE, MAP_SHARED | MAP_FIXED | MAP_ANONYMOUS,
0, 0) == MAP_FAILED) {
perror("Error: ");
exit(1);
}
/* Copy the original data back to the counter-region */
memcpy(&__FUZZ_COUNTERS_START, copy,
&__FUZZ_COUNTERS_END - &__FUZZ_COUNTERS_START);
free(copy);
}

23
tests/qtest/fuzz/fork_fuzz.h
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@ -1,23 +0,0 @@
/*
* Fork-based fuzzing helpers
*
* Copyright Red Hat Inc., 2019
*
* Authors:
* Alexander Bulekov <alxndr@bu.edu>
*
* This work is licensed under the terms of the GNU GPL, version 2 or later.
* See the COPYING file in the top-level directory.
*
*/
#ifndef FORK_FUZZ_H
#define FORK_FUZZ_H
extern uint8_t __FUZZ_COUNTERS_START;
extern uint8_t __FUZZ_COUNTERS_END;
void counter_shm_init(void);
#endif

56
tests/qtest/fuzz/fork_fuzz.ld
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@ -1,56 +0,0 @@
/*
* We adjust linker script modification to place all of the stuff that needs to
* persist across fuzzing runs into a contiguous section of memory. Then, it is
* easy to re-map the counter-related memory as shared.
*/
SECTIONS
{
.data.fuzz_start : ALIGN(4K)
{
__FUZZ_COUNTERS_START = .;
__start___sancov_cntrs = .;
*(_*sancov_cntrs);
__stop___sancov_cntrs = .;
/* Lowest stack counter */
*(__sancov_lowest_stack);
}
}
INSERT AFTER .data;
SECTIONS
{
.data.fuzz_ordered :
{
/*
* Coverage counters. They're not necessary for fuzzing, but are useful
* for analyzing the fuzzing performance
*/
__start___llvm_prf_cnts = .;
*(*llvm_prf_cnts);
__stop___llvm_prf_cnts = .;
/* Internal Libfuzzer TracePC object which contains the ValueProfileMap */
FuzzerTracePC*(.bss*);
/*
* In case the above line fails, explicitly specify the (mangled) name of
* the object we care about
*/
*(.bss._ZN6fuzzer3TPCE);
}
}
INSERT AFTER .data.fuzz_start;
SECTIONS
{
.data.fuzz_end : ALIGN(4K)
{
__FUZZ_COUNTERS_END = .;
}
}
/*
* Don't overwrite the SECTIONS in the default linker script. Instead insert the
* above into the default script
*/
INSERT AFTER .data.fuzz_ordered;

6
tests/qtest/fuzz/meson.build
View File

@ -2,7 +2,7 @@ if not get_option('fuzzing')
subdir_done()
endif
specific_fuzz_ss.add(files('fuzz.c', 'fork_fuzz.c', 'qos_fuzz.c',
specific_fuzz_ss.add(files('fuzz.c', 'qos_fuzz.c',
'qtest_wrappers.c'), qos)
# Targets
@ -12,7 +12,7 @@ specific_fuzz_ss.add(when: 'CONFIG_VIRTIO_SCSI', if_true: files('virtio_scsi_fuz
specific_fuzz_ss.add(when: 'CONFIG_VIRTIO_BLK', if_true: files('virtio_blk_fuzz.c'))
specific_fuzz_ss.add(files('generic_fuzz.c'))
fork_fuzz = declare_dependency(
fuzz_ld = declare_dependency(
link_args: fuzz_exe_ldflags +
['-Wl,-wrap,qtest_inb',
'-Wl,-wrap,qtest_inw',
@ -35,4 +35,4 @@ fork_fuzz = declare_dependency(
'-Wl,-wrap,qtest_memset']
)
specific_fuzz_ss.add(fork_fuzz)
specific_fuzz_ss.add(fuzz_ld)