linux-kernel - Re: [PATCH V8 0/2] printk: hash addresses printed with %p

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Message-ID: <20171031231619.GB3585@eros>
Date:   Wed, 1 Nov 2017 10:16:19 +1100
From:   "Tobin C. Harding" <me@...in.cc>
To:     Joe Perches <joe@...ches.com>
Cc:     Kees Cook <keescook@...omium.org>,
        kernel-hardening@...ts.openwall.com,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Theodore Ts'o <tytso@....edu>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Tycho Andersen <tycho@...ker.com>,
        "Roberts, William C" <william.c.roberts@...el.com>,
        Tejun Heo <tj@...nel.org>,
        Jordan Glover <Golden_Miller83@...tonmail.ch>,
        Greg KH <gregkh@...uxfoundation.org>,
        Petr Mladek <pmladek@...e.com>,
        Ian Campbell <ijc@...lion.org.uk>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <wilal.deacon@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Chris Fries <cfries@...gle.com>,
        Dave Weinstein <olorin@...gle.com>,
        Daniel Micay <danielmicay@...il.com>,
        Djalal Harouni <tixxdz@...il.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V8 0/2] printk: hash addresses printed with %p

On Mon, Oct 30, 2017 at 07:08:48PM -0700, Joe Perches wrote:
> On Tue, 2017-10-31 at 09:33 +1100, Tobin C. Harding wrote:
> > On Mon, Oct 30, 2017 at 03:03:21PM -0700, Kees Cook wrote:
> > > On Wed, Oct 25, 2017 at 7:53 PM, Tobin C. Harding <me@...in.cc> wrote:
> > > > Here is the behaviour that this set implements.
> > > > 
> > > > For kpt_restrict==0
> > > > 
> > > > Randomness not ready:
> > > >   printed with %p:              (pointer)          # NOTE: with padding
> > > > Valid pointer:
> > > >   printed with %pK:             deadbeefdeadbeef
> > > >   printed with %p:              0xdeadbeef
> > > >   malformed specifier (eg %i):  0xdeadbeef
> > > 
> > > I really think we can't include SPECIAL unless _every_ callsite of %p
> > > is actually doing "0x%p", and then we're replacing all of those. We're
> > > not doing that, though...
> > > 
> > > $ git grep '%p\b' | wc -l
> > > 12766
> > > $ git grep '0x%p\b' | wc -l
> > > 18370x
> > > 
> > > If we need some kind of special marking that this is a hashed
> > > variable, that should be something other than "0x". If we're using the
> > > existing "(null)" and new "(pointer)" text, maybe "(hash:xxxxxx)"
> > > should be used instead? Then the (rare) callers with 0x become
> > > "0x(hash:xxxx)" and naked callers produce "(hash:xxxx)".
> > > 
> > > I think the first step for this is to just leave SPECIAL out.
> > 
> > Thanks Kees. V9 leaves SPECIAL out. Also V9 prints the whole 64 bit
> > address with the first 32 bits masked to zero. The intent being to _not_
> > change the output format from what it currently is. So it will look like
> > this; 
> > 
> > 	00000000c09e81d0
> > 
> > What do you think?
> > 
> > Amusingly I think this whole conversation is going to come up again
> > when we do %pa, in inverse, since %pa currently does us SPECIAL.
> 
> I once sent a patch set to remove SPECIAL from %pa
> and add 0x where necessary.
> 
> https://patchwork.kernel.org/patch/3875471/
> 
> After that didn't happen, I removed the duplicated
> 0x%pa with a sed.
> 
> https://patchwork.kernel.org/patch/8509421/
> 
> Sending a treewide sed patch would be fine with me.

Cool, thanks Joe I'll keep this in mind for when we get to %pa.

thanks,
Tobin.