Re: [git pull] uaccess-related bits of vfs.git

Ingo Molnar
2017-05-14T18:14:02Z

* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Fri, May 12, 2017 at 11:57 PM, Al Viro <viro@zeniv.linux.org.uk> wrote:
> >
> > First, some stats: there's a thousand-odd callers of __get_user(). Out of
> > those, about 70% are in arch/, mostly in sigframe-related code.
>
> Sure. And they can be trivially converted, and none of them should care at all.
>
> > IOW, we have
> > * most of users in arch/* (heavily dominated by signal-related code,
> > both loads and stores). Those need careful massage; maybe unsafe-based
> > solution, maybe something else, but it's obviously per-architecture work
> > and these paths are sensitive.
>
> Why are they sensitive?
>
> Why not just do this:
>
> git grep -l '\<__\(\(get\)\|\(put\)\)_user(' -- arch/x86
> :^arch/x86/include/asm/uaccess.h
> | xargs sed -i 's/__\(\(\(get\)\|\(put\)\)_user(\)/\1/g'
>
> which converts all the x86 uses in one go.
>
> Anybody who *relies* on not checking the address_limit is so broken as
> to be not even funny. And anything that is so performance-sensitive
> that anybody can even measure the effect of the above we can convert
> later.

I'd say that the CLAC/STAC addition pretty much killed any argument in favor of
"optimized" __get_user() code, so I'd be very happy to see these interfaces gone
altogether.

So as far as x86 usage goes:

Acked-by: Ingo Molnar <mingo@kernel.org>

Thanks,

Ingo