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

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Message-ID: <20170514181356.whn26wtc7aorpxvc@gmail.com>
Date:   Sun, 14 May 2017 20:13:56 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
Subject: Re: [git pull] uaccess-related bits of vfs.git


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

> On Fri, May 12, 2017 at 11:57 PM, Al Viro <viro@...iv.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@...nel.org>

Thanks,

	Ingo