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

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Message-ID: <20190307184813.GL32477@hirez.programming.kicks-ass.net>
Date:   Thu, 7 Mar 2019 19:48:13 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     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>,
        Josh Poimboeuf <jpoimboe@...hat.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 Thu, Mar 07, 2019 at 09:54:14AM -0800, Linus Torvalds wrote:
> On Thu, Mar 7, 2019 at 9:41 AM Peter Zijlstra <peterz@...radead.org> wrote:
> > >
> > > What's the call site that made you go "just add __memset() to the list"?
> >
> > __asan_{,un}poinson_stack_memory()
> >   kasan_{,un}poison_shadow()
> >     __memset()
> 
> Ugh. I think I almost just agree with your decision to just let that
> memset go unchecked.
> 
> I'm not saying it's right, but it doesn't seem to be a fight worth fighting.

One think I could do; is add a filter to each function and only allow
__memset from the kasan code, and not from anywhere else.

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.

> Because AC vs KASAN in general ends up smelling like "not a fight
> worth fighting" to me. You've done a herculean job, but..

I know,.. I've been so close to doing that so many times, but it
seems like defeat, esp. since I'm so close now :-)