linux-kernel - Re: [PATCH v3] mm/usercopy: get rid of CONFIG_DEBUG_STRICT_USER_COPY

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Message-ID: <CA+55aFzUGGFUvjkTy1tK7VqO-M7iQTOAzn3n6dHoxohTqK4rhg@mail.gmail.com>
Date:   Tue, 30 Aug 2016 10:02:38 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Steven Rostedt <rostedt@...dmis.org>,
        Brian Gerst <brgerst@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Byungchul Park <byungchul.park@....com>,
        Nilay Vaish <nilayvaish@...il.com>
Subject: Re: [PATCH v3] mm/usercopy: get rid of CONFIG_DEBUG_STRICT_USER_COPY_CHECKS

On Tue, Aug 30, 2016 at 6:04 AM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> There are three usercopy warnings which are currently being silenced for
> gcc 4.6 and newer:

[.. snip snip ..]

Ok, I'm not entirely happy with the timing, but I think the problem
counts as a regression since it effectively made all the checks go
away in practice for most people, so I'm going to apply this patch.

I know Al Viro is working on some uaccess cleanups and trying to make
a lot of this be generic, so there's hopefully cleanups coming in the
not too distant future (I say "hopefully", because I worry that
looking at the mess will make Al dig his eyes out), but this seems to
be a clear improvement.

I still do wish we'd move the x86 __builtin_constant_p(n) check
around, so that x86 wouldn't do the run-time check_object_size() for
the trivially statically correct case, but I guess that's a separate
issue from this patch anyway.

If somebody has objections to this patch, holler quickly, because it's
about to get applied. 3.. 2.. 1..

                         Linus