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disable compare-transform-pass when lto_mode and autodictionary is used.

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hexcoder-
2020-04-15 22:27:32 +02:00
parent 21f696f02e
commit 7e2c52f2b9
2 changed files with 12 additions and 10 deletions
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16
llvm_mode/README.lto.md
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@ -17,17 +17,17 @@ This version requires a current llvm 11 compiled from the github master.
## Introduction and problem description ## Introduction and problem description
A big issue with how afl/afl++ works is that the basic block IDs that are A big issue with how afl/afl++ works is that the basic block IDs that are
set during compilation are random - and hence natually the larger the number set during compilation are random - and hence naturally the larger the number
of instrumented locations, the higher the number of edge collisions in the of instrumented locations, the higher the number of edge collisions are in the
map. This can result in not discovering new paths and therefore degrade the map. This can result in not discovering new paths and therefore degrade the
efficiency of the fuzzing. efficiency of the fuzzing process.
*This issue is understimated in the fuzzing community!* *This issue is underestimated in the fuzzing community!*
With a 2^16 = 64kb standard map at already 256 instrumented blocks there is With a 2^16 = 64kb standard map at already 256 instrumented blocks there is
on average one collision. On average a target has 10.000 to 50.000 on average one collision. On average a target has 10.000 to 50.000
instrumented blocks hence the real collisions are between 750-18.000! instrumented blocks hence the real collisions are between 750-18.000!
To get to a solution that prevents any collision took several approaches To reach a solution that prevents any collisions took several approaches
and many dead ends until we got to this: and many dead ends until we got to this:
* We instrument at link time when we have all files pre-compiled * We instrument at link time when we have all files pre-compiled
@ -76,7 +76,7 @@ $ make install
## How to use afl-clang-lto ## How to use afl-clang-lto
Just use afl-clang-lto like you did afl-clang-fast or afl-gcc. Just use afl-clang-lto like you did with afl-clang-fast or afl-gcc.
Also whitelisting (AFL_LLVM_WHITELIST -> [README.whitelist.md](README.whitelist.md)) and Also whitelisting (AFL_LLVM_WHITELIST -> [README.whitelist.md](README.whitelist.md)) and
laf-intel/compcov (AFL_LLVM_LAF_* -> [README.laf-intel.md](README.laf-intel.md)) work. laf-intel/compcov (AFL_LLVM_LAF_* -> [README.laf-intel.md](README.laf-intel.md)) work.
@ -120,7 +120,7 @@ Please report issues at:
## Upcoming Work ## Upcoming Work
1. Currently the LTO whitelist feature does not allow to not instrument main, 1. Currently the LTO whitelist feature does not allow to instrument main,
start and init functions start and init functions
## History ## History
@ -138,7 +138,7 @@ This was first implemented in January and work ... kinda.
The LTO time instrumentation worked, however the "how" the basic blocks were The LTO time instrumentation worked, however the "how" the basic blocks were
instrumented was a problem, as reducing duplicates turned out to be very, instrumented was a problem, as reducing duplicates turned out to be very,
very difficult with a program that has so many paths and therefore so many very difficult with a program that has so many paths and therefore so many
dependencies. At lot of stratgies were implemented - and failed. dependencies. At lot of strategies were implemented - and failed.
And then sat solvers were tried, but with over 10.000 variables that turned And then sat solvers were tried, but with over 10.000 variables that turned
out to be a dead-end too. out to be a dead-end too.

6
llvm_mode/afl-clang-fast.c
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@ -223,8 +223,10 @@ static void edit_params(u32 argc, char **argv, char **envp) {
} }
if (getenv("LAF_TRANSFORM_COMPARES") || if (!getenv("AFL_LLVM_LTO_AUTODICTIONARY") // disabled when autodictionary
getenv("AFL_LLVM_LAF_TRANSFORM_COMPARES")) { && instrument_mode != INSTRUMENT_LTO // and lto_mode is used
&& (getenv("LAF_TRANSFORM_COMPARES") ||
getenv("AFL_LLVM_LAF_TRANSFORM_COMPARES"))) {
cc_params[cc_par_cnt++] = "-Xclang"; cc_params[cc_par_cnt++] = "-Xclang";
cc_params[cc_par_cnt++] = "-load"; cc_params[cc_par_cnt++] = "-load";