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Diffstat (limited to 'docs/perf_tips.md')
| -rw-r--r-- | docs/perf_tips.md | 47 |
1 files changed, 17 insertions, 30 deletions
diff --git a/docs/perf_tips.md b/docs/perf_tips.md index c5968206..9c31e56b 100644 --- a/docs/perf_tips.md +++ b/docs/perf_tips.md @@ -48,13 +48,9 @@ be then manually fed to a more resource-hungry program later on. Also note that reading the fuzzing input via stdin is faster than reading from a file. -## 3. Use LLVM instrumentation +## 3. Use LLVM persistent instrumentation -When fuzzing slow targets, you can gain 20-100% performance improvement by -using the LLVM-based instrumentation mode described in [the instrumentation README](../instrumentation/README.llvm.md). -Note that this mode requires the use of clang and will not work with GCC. - -The LLVM mode also offers a "persistent", in-process fuzzing mode that can +The LLVM mode offers a "persistent", in-process fuzzing mode that can work well for certain types of self-contained libraries, and for fast targets, can offer performance gains up to 5-10x; and a "deferred fork server" mode that can offer huge benefits for programs with high startup overhead. Both @@ -138,8 +134,7 @@ misses, or similar factors, but they are less likely to be a concern.) ## 7. Keep memory use and timeouts in check -If you have increased the `-m` or `-t` limits more than truly necessary, consider -dialing them back down. +Consider setting low values for `-m` and `-t`. For programs that are nominally very fast, but get sluggish for some inputs, you can also try setting `-t` values that are more punishing than what `afl-fuzz` @@ -164,6 +159,20 @@ There are several OS-level factors that may affect fuzzing speed: - Network filesystems, either used for fuzzer input / output, or accessed by the fuzzed binary to read configuration files (pay special attention to the home directory - many programs search it for dot-files). + - Disable all the spectre, meltdown etc. security countermeasures in the + kernel if your machine is properly separated: + +``` +ibpb=off ibrs=off kpti=off l1tf=off mds=off mitigations=off +no_stf_barrier noibpb noibrs nopcid nopti nospec_store_bypass_disable +nospectre_v1 nospectre_v2 pcid=off pti=off spec_store_bypass_disable=off +spectre_v2=off stf_barrier=off +``` + In most Linux distributions you can put this into a `/etc/default/grub` + variable. + +The following list of changes are made when executing `afl-system-config`: + - On-demand CPU scaling. The Linux `ondemand` governor performs its analysis on a particular schedule and is known to underestimate the needs of short-lived processes spawned by `afl-fuzz` (or any other fuzzer). On Linux, @@ -196,26 +205,4 @@ There are several OS-level factors that may affect fuzzing speed: Setting a different scheduling policy for the fuzzer process - say `SCHED_RR` - can usually speed things up, too, but needs to be done with care. - - Use the `afl-system-config` script to set all proc/sys settings above in one go. - - Disable all the spectre, meltdown etc. security countermeasures in the - kernel if your machine is properly separated: - -``` -ibpb=off ibrs=off kpti=off l1tf=off mds=off mitigations=off -no_stf_barrier noibpb noibrs nopcid nopti nospec_store_bypass_disable -nospectre_v1 nospectre_v2 pcid=off pti=off spec_store_bypass_disable=off -spectre_v2=off stf_barrier=off -``` - In most Linux distributions you can put this into a `/etc/default/grub` - variable. - -## 9. If all other options fail, use `-d` - -For programs that are genuinely slow, in cases where you really can't escape -using huge input files, or when you simply want to get quick and dirty results -early on, you can always resort to the `-d` mode. -The mode causes `afl-fuzz` to skip all the deterministic fuzzing steps, which -makes output a lot less neat and can ultimately make the testing a bit less -in-depth, but it will give you an experience more familiar from other fuzzing -tools. |