sandsifter

s a n d s i f t e r : the x86 processor fuzzer Overview The sandsifter audits x86 processors for hidden instructions and hardware bugs, by systematically generating machine code to search through a processor's instruction set, and monitoring execution for anomalies. Sandsifter has uncovered secret processor instructions from every major vendor; ubiquitous software bugs in disassemblers, assemblers, and emulators; flaws in enterprise hypervisors; and both benign and security-critical hardware bugs in x86 chips. With the multitude of x86 processors in existence, the goal of the tool is to enable users to check their own systems for hidden instructions and bugs. To run a basic audit against your processor: sudo ./sifter.py --unk --dis --len --sync --tick -- -P1 -t The computer is systematically scanned for anomalous instructions. In the upper half, you can view the instructions that the sandsifter is currently testing on the processor. In the bottom half, the sandsifter reports anomalies it finds. The search will take from a few hours to a few days, depending on the speed of and complexity of your processor. When it is complete, summarize the results: ./summarize.py data/log Typically, several million undocumented instructions on your processor will be found, but these generally fall into a small number of different groups. After binning the anomalies, the summarize tool attempts to assign each instruction to an issue category: Software bug (for example, a bug in your hypervisor or disassembler), Hardware bug (a bug in your CPU), or Undocumented instruction (an instruction that exists in the processor, but is not acknowledged by the manufacturer) Press 'Q' to quit and obtain a text based summary of the system scan: The results of a scan can sometimes be difficult for the tools to automatically classify, and may require manual analysis. For help analyzing your results, feel free to send the ./data/log file to xoreaxeaxeax@gmail.com. No personal information, other than the processor make, model, and revision (from /proc/cpuinfo) are included in this log. Results Scanning with the sandsifter has uncovered undocumented processor features across dozens of opcode categories, flaws in enterprise hypervisors, bugs in nearly every major disassembly and emulation tool, and critical hardware bugs opening security vulnerabilities in the processor itself. Details of the results can be found in the project whitepaper. (TODO: detailed results enumeration here) Building Sandsifter requires first installing the Capstone disassembler: http://www.capstone-engine.org/. Capstone can typically be installed with: sudo apt-get install libcapstone3 libcapstone-dev sudo pip install capstone Sandsifter can be built with: make and is then run with sudo ./sifter.py --unk --dis --len --sync --tick -- -P1 -t Flags Flags are passed to the sifter with --flag, and to the injector with -- -f. Example: sudo ./sifter.py --unk --dis --len --sync --tick -- -P1 -t Sifter flags: --len search for length differences in all instructions (instructions that executed differently than the disassembler expected, or did not exist when the disassembler expected them to --dis search for length differences in valid instructions (instructions that executed differently than the disassembler expected) --unk search for unknown instructions (instructions that the disassembler doesn't know about but successfully execute) --ill the inverse of --unk, search for invalid disassemblies (instructions that do not successfully execute but that the disassembler acknowledges) --tick periodically write the current instruction to disk --save save search progress on exit --resume resume search from last saved state --sync write search results to disk as they are found --low-mem do not store results in memory Injector flags: -b mode: brute force -r mode: randomized fuzzing -t mode: tunneled fuzzing -d mode: externally directed fuzzing -R raw output mode -T text output mode -x write periodic progress to stderr -0 allow null dereference (requires sudo) -D allow duplicate prefixes -N no nx bit support -s seed in random search, seed value -B brute_depth in brute search, maximum search depth -P max_prefix maximum number of prefixes to search -i instruction instruction at which to start search (inclusive) -e instruction instruction at which to end search (exclusive) -c core core on which to perform search -X blacklist blacklist the specified instruction -j jobs number of simultaneous jobs to run -l range_bytes number of base instruction bytes in each sub range Keys m: Mode - change the search mode (brute force, random, or tunnel) for the sifter q: Quit - exit the sifter p: Pause - pause or unpause the search Algorithms The scanning supports four different search algorithms, which can be set at the command line, or cycled via hotkeys. Random searching generates random instructions to test; it generally produces results quickly, but is unable to find complex hidden instructions and bugs. Brute force searching tries instructions incrementally, up to a user-specified length; in almost all situations, it performs worse than random searching. Driven or mutation driven searching is designed to create new, increasingly complex instructions through genetic algorithms; while promising, this approach was never fully realized, and is left as a stub for future research. Tunneling is the approach described in the presentation and white paper, and in almost all cases provides the best trade-off between thoroughness and speed. Tips sudo For best results, the tool should be run as the root user. This is necessary so that the process can map into memory a page at address 0, which requires root permissions. This page prevents many instructions from seg-faulting on memory accesses, which allows a more accurate fault analysis. Prefixes The primary limitation for the depth of an instruction search is the n