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README.dislocator

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+===================================
+libdislocator, an abusive allocator
+===================================
+
+  (See ../docs/README for the general instruction manual.)
+
+This is a companion library that can be used as a drop-in replacement for the
+libc allocator in the fuzzed binaries. It improves the odds of bumping into
+heap-related security bugs in several ways:
+
+  - It allocates all buffers so that they are immediately adjacent to a
+    subsequent PROT_NONE page, causing most off-by-one reads and writes to
+    immediately segfault,
+
+  - It adds a canary immediately below the allocated buffer, to catch writes
+    to negative offsets (won't catch reads, though),
+
+  - It sets the memory returned by malloc() to garbage values, improving the
+    odds of crashing when the target accesses uninitialized data,
+
+  - It sets freed memory to PROT_NONE and does not actually reuse it, causing
+    most use-after-free bugs to segfault right away,
+
+  - It forces all realloc() calls to return a new address - and sets
+    PROT_NONE on the original block. This catches use-after-realloc bugs,
+
+  - It checks for calloc() overflows and can cause soft or hard failures
+    of alloc requests past a configurable memory limit (AFL_LD_LIMIT_MB,
+    AFL_LD_HARD_FAIL).
+
+Basically, it is inspired by some of the non-default options available for the
+OpenBSD allocator - see malloc.conf(5) on that platform for reference. It is
+also somewhat similar to several other debugging libraries, such as gmalloc
+and DUMA - but is simple, plug-and-play, and designed specifically for fuzzing
+jobs.
+
+Note that it does nothing for stack-based memory handling errors. The
+-fstack-protector-all setting for GCC / clang, enabled when using AFL_HARDEN,
+can catch some subset of that.
+
+The allocator is slow and memory-intensive (even the tiniest allocation uses up
+4 kB of physical memory and 8 kB of virtual mem), making it completely unsuitable
+for "production" uses; but it can be faster and more hassle-free than ASAN / MSAN
+when fuzzing small, self-contained binaries.
+
+To use this library, run AFL like so:
+
+AFL_PRELOAD=/path/to/libdislocator.so ./afl-fuzz [...other params...]
+
+You *have* to specify path, even if it's just ./libdislocator.so or
+$PWD/libdislocator.so.
+
+Similarly to afl-tmin, the library is not "proprietary" and can be used with
+other fuzzers or testing tools without the need for any code tweaks. It does not
+require AFL-instrumented binaries to work.
+
+Note that the AFL_PRELOAD approach (which AFL internally maps to LD_PRELOAD or
+DYLD_INSERT_LIBRARIES, depending on the OS) works only if the target binary is
+dynamically linked. Otherwise, attempting to use the library will have no
+effect.