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SubjectRe: [PATCH v4 0/5] x86 instruction emulator fuzzing
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> On Jul 3, 2019, at 12:20 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> On 28/06/19 11:33, Alexander Graf wrote:
>>
>>
>> On 28.06.19 11:26, Sam Caccavale wrote:
>>> Dear all,
>>>
>>> This series aims to provide an entrypoint for, and fuzz KVM's x86
>>> instruction
>>> emulator from userspace. It mirrors Xen's application of the AFL
>>> fuzzer to
>>> it's instruction emulator in the hopes of discovering vulnerabilities.
>>> Since this entrypoint also allows arbitrary execution of the emulators
>>> code
>>> from userspace, it may also be useful for testing.
>>>
>>> The current 4 patches build the emulator and 2 harnesses:
>>> simple-harness is
>>> an example of unit testing; afl-harness is a frontend for the AFL fuzzer.
>>> The fifth patch contains useful scripts for development but is not
>>> intended
>>> for usptream consumption.
>>>
>>> Patches
>>> =======
>>>
>>> - 01: Builds and links afl-harness with the required kernel objects.
>>> - 02: Introduces the minimal set of emulator operations and supporting
>>> code
>>> to emulate simple instructions.
>>> - 03: Demonstrates simple-harness as a unit test.
>>> - 04: Adds scripts for install and building.
>>> - 05: Useful scripts for development
>>>
>>>
>>> Issues
>>> =======
>>>
>>> Currently, fuzzing results in a large amount of FPU related crashes.
>>> Xen's
>>> fuzzing efforts had this issue too. Their (temporary?) solution was to
>>> disable FPU exceptions after every instruction iteration? Some solution
>>> is desired for this project.
>>>
>>>
>>> Changelog
>>> =======
>>>
>>> v1 -> v2:
>>> - Moved -O0 to ifdef DEBUG
>>> - Building with ASAN by default
>>> - Removed a number of macros from emulator_ops.c and moved them as
>>> static inline functions in emulator_ops.h
>>> - Accidentally changed the example in simple-harness (reverted in v3)
>>> - Introduced patch 4 for scripts
>>>
>>> v2 -> v3:
>>> - Removed a workaround for printf smashing the stack when compiled
>>> with -mcmodel=kernel, and stopped compiling with -mcmodel=kernel
>>> - Added a null check for malloc's return value
>>> - Moved more macros from emulator_ops.c into emulator_ops.h as
>>> static inline functions
>>> - Removed commented out code
>>> - Moved changes to emulator_ops.h into the first patch
>>> - Moved addition of afl-many script to the script patch
>>> - Fixed spelling mistakes in documentation
>>> - Reverted the simple-harness example back to the more useful
>>> original one
>>> - Moved non-essential development scripts from patch 4 to new patch 5
>>>
>>> v3 -> v4:
>>> - Stubbed out all unimplemented emulator_ops with a unimplemented_op
>>> macro
>>> - Setting FAIL_ON_UNIMPLEMENTED_OP on compile decides whether
>>> calling these
>>> is treated as a crash or ignored
>>> - Moved setting up core dumps out of the default build/install path and
>>> detailed this change in the README
>>> - Added a .sh extention to afl-many
>>> - Added an optional timeout to afl-many.sh and made deploy_remote.sh
>>> use it
>>> - Building no longer creates a new .config each time and does not
>>> force any
>>> config options
>>> - Fixed a path bug in afl-many.sh
>>>
>>> Any comments/suggestions are greatly appreciated.
>>>
>>> Best,
>>> Sam Caccavale
>>>
>>> Sam Caccavale (5):
>>> Build target for emulate.o as a userspace binary
>>> Emulate simple x86 instructions in userspace
>>> Demonstrating unit testing via simple-harness
>>> Added build and install scripts
>>> Development scripts for crash triage and deploy
>>>
>>> tools/Makefile | 9 +
>>> tools/fuzz/x86ie/.gitignore | 2 +
>>> tools/fuzz/x86ie/Makefile | 54 ++
>>> tools/fuzz/x86ie/README.md | 21 +
>>> tools/fuzz/x86ie/afl-harness.c | 151 +++++
>>> tools/fuzz/x86ie/common.h | 87 +++
>>> tools/fuzz/x86ie/emulator_ops.c | 590 ++++++++++++++++++
>>> tools/fuzz/x86ie/emulator_ops.h | 134 ++++
>>> tools/fuzz/x86ie/scripts/afl-many.sh | 31 +
>>> tools/fuzz/x86ie/scripts/bin.sh | 49 ++
>>> tools/fuzz/x86ie/scripts/build.sh | 34 +
>>> tools/fuzz/x86ie/scripts/coalesce.sh | 5 +
>>> tools/fuzz/x86ie/scripts/deploy.sh | 9 +
>>> tools/fuzz/x86ie/scripts/deploy_remote.sh | 10 +
>>> tools/fuzz/x86ie/scripts/gen_output.sh | 11 +
>>> tools/fuzz/x86ie/scripts/install_afl.sh | 15 +
>>> .../fuzz/x86ie/scripts/install_deps_ubuntu.sh | 5 +
>>> tools/fuzz/x86ie/scripts/rebuild.sh | 6 +
>>> tools/fuzz/x86ie/scripts/run.sh | 10 +
>>> tools/fuzz/x86ie/scripts/summarize.sh | 9 +
>>> tools/fuzz/x86ie/simple-harness.c | 49 ++
>>> tools/fuzz/x86ie/stubs.c | 59 ++
>>> tools/fuzz/x86ie/stubs.h | 52 ++
>>
>> Sorry I didn't realize it before. Isn't that missing a patch to the
>> MAINTAINERS file?

It is, I will add that.

> Yeah, and the directory should probably be tools/fuzz/kvm_emulate so as
> not to puzzle people. Also:
>
> - let's limit the scripts to the minimum, i.e. only the run script which
> should be something like
>
> #!/bin/bash
> # SPDX-License-Identifier: GPL-2.0+
>
> FUZZDIR="${FUZZDIR:-$(pwd)/fuzz}"
>
> mkdir -p $FUZZDIR/in
> cp tools/fuzz/kvm_emulate/rand_sample.bin $FUZZDIR/in
> mkdir -p $FUZZDIR/out
>
> ${TIMEOUT:+TIMEOUT=$TIMEOUT} ${AFL_FUZZ-afl-fuzz} "$@" \
> -i $FUZZDIR/in -o $FUZZDIR/out tools/fuzz/kvm_emulate/afl-harness @@
>
> where people can substitute afl-many.sh or add their own options using
> the AFL_FUZZ variable or the command line. Likewise for screen.

Yep, both of those are sensible. I’ll update with next patch.

> - the build should be just "make -C tools/fuzz/kvm_emulate" and it
> should just work. Feel free to steal the Makefile magic from other
> tools/ directories.

Yeah, the build is a bit of a sore point. I’ll reach out if I can’t get it to work.

> - finally, rand_sample.bin is missing.
>
> Otherwise, it looks very nice.
>
> Paolo

Thanks for the feedback.

Per the email’s bouncing, I’ve removed my @amazon.de email and will be using this one going forward.

- Sam

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