linux-kernel - Re: [PATCH v4 0/5] x86 instruction emulator fuzzing

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Message-ID: <caaeb546-9aa1-7fd5-496d-a0ec1f759d10@amazon.com>
Date:   Fri, 28 Jun 2019 11:33:45 +0200
From:   Alexander Graf <graf@...zon.com>
To:     Sam Caccavale <samcacc@...zon.de>
CC:     <samcaccavale@...il.com>, <nmanthey@...zon.de>,
        <wipawel@...zon.de>, <dwmw@...zon.co.uk>, <mpohlack@...zon.de>,
        <karahmed@...zon.de>, <andrew.cooper3@...rix.com>,
        <JBeulich@...e.com>, <pbonzini@...hat.com>, <rkrcmar@...hat.com>,
        <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
        <hpa@...or.com>, <paullangton4@...il.com>, <x86@...nel.org>,
        <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 0/5] x86 instruction emulator fuzzing



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?


Alex