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qemu_taint

First level taint implementation with qemu for linux user mode

How to use with afl++

WIP

This is meant for afl++. Checkout this special branch of afl++: taint branch Then in the afl++ repository execute cd qemu_taint && ./build_qemu_taint.sh. To use it just add the -A flag to afl-fuzz.

How to use stand-alone

Building

./build.sh

Currently only x86_64 is tested for host and guest, others could work though.

Running

Just run your target with afl-qemu-taint -- program flags. By default the taint is gathered on stdin reads. To see taint from files you have to set the environment variable AFL_TAINT_INPUT with the full path to the input file.

The output

[TAINT] MAP (length: 56, shown: 56) ('!' = touched, '.' = untouched)
[ .!..!!!!....!!!!!!!!!!!!!!!!!!!!!!!.....................         ]

Debug output

Set DEBUG=1 (or AFL_DEBUG=1).

This prints all the syscalls that touch the filename and tainted file descriptors plus the tainted memory operations.

Caveats

  1. only tested for x86_x64 for host and guest (but could work elsewhere too)

  2. Some syscall are not covered:

  • NR_remap_file_pages, NR_copy_file_range: these are not implemented in qemu
  • NR_sendfile, NR_sendfile64: write directly to a fd, so no memory access. This is not interpretated as taint. However a warning is given.
  • NR_[f]truncate, NR_[f]truncate64: only if it truncates to 0 we stop watching for open*, otherwise it is ignored
  • NR_open_by_handle_at: not supported (PRs welcome)

  1. Complex things will not be detected, e.g. a rename or symlink on the file and then working on it.

  2. No care for speed. It is fast enough but could be made faster.