Re: [PATCH v2] Add kernel config option for fuzz testing.

Jiri Slaby
2020-03-07T16:30:25Z

On 07. 03. 20, 14:58, Tetsuo Handa wrote:
> While syzkaller is finding many bugs, sometimes syzkaller examines
> stupid operations. Currently we prevent syzkaller from examining
> stupid operations by blacklisting syscall arguments and/or disabling
> whole functionality using existing kernel config options, but it is
> a whack-a-mole approach. We need cooperation from kernel side [1].
>
> This patch introduces a kernel config option which allows disabling
> only specific operations. This kernel config option should be enabled
> only when building kernels for fuzz testing.
>
> We discussed possibility of disabling specific operations at run-time
> using some lockdown mechanism [2], but conclusion seems that build-time
> control (i.e. kernel config option) fits better for this purpose.
> Since patches for users of this kernel config option will want a lot of
> explanation [3], this patch provides only kernel config option for them.
>
> [1] https://github.com/google/syzkaller/issues/1622
> [2] https://lkml.kernel.org/r/CACdnJutc7OQeoor6WLTh8as10da_CN=crs79v3Fp0mJTaO=+yw@mail.gmail.com
> [3] https://lkml.kernel.org/r/20191216163155.GB2258618@kroah.com
>
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Cc: Dmitry Vyukov <dvyukov@google.com>
> ---
> lib/Kconfig.debug | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> Changes since v1:
> Drop users of this kernel config option.
> Update patch description.
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 53e786e0a604..e360090e24c5 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -2208,4 +2208,14 @@ config HYPERV_TESTING
>
> endmenu # "Kernel Testing and Coverage"
>
> +config KERNEL_BUILT_FOR_FUZZ_TESTING
> + bool "Build kernel for fuzz testing"

If we really want to go this way, I wouldn't limit it for fuzz testing
only. Static analyzers, symbolic executors, formal verifiers, etc. --
all of them should avoid the paths.

So what about KERNEL_BUILT_FOR_ANALYZERS?

> + default n
> + help
> + Say N unless you are building kernels for fuzz testing.
> + Saying Y here disables several things that legitimately cause
> + damage under a fuzzer workload (e.g. copying to arbitrary
> + user-specified kernel address, changing console loglevel,
> + freezing filesystems).
> +
> endmenu # Kernel hacking
>

--
js
suse labs