linux-kernel - Re: [PATCH 18/20] objtool: Add UACCESS validation

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Message-ID: <20190308152318.GC32494@hirez.programming.kicks-ass.net>
Date:   Fri, 8 Mar 2019 16:23:18 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Anvin <hpa@...or.com>,
        Julien Thierry <julien.thierry@....com>,
        Will Deacon <will.deacon@....com>,
        Andy Lutomirski <luto@...capital.net>,
        Ingo Molnar <mingo@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        James Morse <james.morse@....com>, valentin.schneider@....com,
        Brian Gerst <brgerst@...il.com>,
        Andrew Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 18/20] objtool: Add UACCESS validation

On Fri, Mar 08, 2019 at 09:07:03AM -0600, Josh Poimboeuf wrote:
> On Thu, Mar 07, 2019 at 09:40:21PM +0100, Peter Zijlstra wrote:
> > On Thu, Mar 07, 2019 at 09:23:19PM +0100, Peter Zijlstra wrote:
> > > On Thu, Mar 07, 2019 at 07:48:13PM +0100, Peter Zijlstra wrote:
> > > > Another thing I need to look at is why objtool only found memset_orig
> > > > (from __memset) but not memset_erms, which if I read the code right, is
> > > > a possible alternative there.
> > > 
> > > Turns out we only look for sibling calls in the original instruction
> > > stream, not in any alternatives; which in general seems like a fair
> > > enough assumption.
> > 
> > And while I'm looking at memset_64.S, why are memset_erms and
> > memset_orig global functions? At the very least they should be local,
> > and ideally not even functions.
> 
> I think the only benefit is that they would show up better on stack
> traces, but that could also be solved by just making them local labels
> inside memset.  Which is what I think they should be.

Boris wanted to use alternative_call_2, just like copy_user_generic().
Which makes more sense to me still.