Re: [stos, again] Re: CVS commit: src/sys/arch/amd64

[Maxime Villard <max%m00nbsd.net@localhost>]

Le 03/06/2020 à 02:03, Kamil Rytarowski a écrit :
> On 03.06.2020 01:49, Andrew Doran wrote:
> > On the assembly thing recall that recently you expressed a desire to remove
> > all of the amd64 assembly string functions from libc because of sanitizers -
> > I invested my time to do up a little demo to try and show you why that's not
> > a good idea:
> >
> > 	http://mail-index.netbsd.org/port-amd64/2020/04/19/msg003226.html
>
> Please note that interceptors for string functions are not just some
> extra burden, but also very useful approach to feedback a fuzzer through
> additional coverage.
>
> At least libFuzzer and honggfuzz wrap many kinds of string functions and
> use it for fuzzing. We should add a special mode in KCOV to feedback
> userland (syzkaller) with traces from string functions.
>
> https://github.com/google/honggfuzz/blob/bbb476eec95ad927d6d7d3d367d2b3e38eed3569/libhfuzz/memorycmp.c#L24

Yes, and not just that either.

When you use ASM instead of C, you basically prevent _any kind_ of useful
transformation the compiler could make.

It includes sanitizers, but also coverage as you said; and also retpoline,
PAC, BTI, CET, SafeStack, and in short, a very big bunch of modern
features.

Favoring C rather than ASM in the general sense offers much bigger
benefits than just "it accomodates kMSan".

Maxime