linux-kernel - Re: [RFC PATCH 09/11] kallsyms: hide layout and expose seed

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Message-ID: <202002270802.1CA8B32AC@keescook>
Date:   Thu, 27 Feb 2020 08:02:37 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Baoquan He <bhe@...hat.com>
Cc:     Kristen Carlson Accardi <kristen@...ux.intel.com>,
        dyoung@...hat.com, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, hpa@...or.com, arjan@...ux.intel.com,
        rick.p.edgecombe@...el.com, x86@...nel.org,
        linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com,
        kexec@...ts.infradead.org
Subject: Re: [RFC PATCH 09/11] kallsyms: hide layout and expose seed

On Thu, Feb 27, 2020 at 10:42:53AM +0800, Baoquan He wrote:
> On 02/06/20 at 09:51am, Kristen Carlson Accardi wrote:
> > On Thu, 2020-02-06 at 04:32 -0800, Kees Cook wrote:
> 
> > > In the past, making kallsyms entirely unreadable seemed to break
> > > weird
> > > stuff in userspace. How about having an alternative view that just
> > > contains a alphanumeric sort of the symbol names (and they will
> > > continue
> > > to have zeroed addresses for unprivileged users)?
> > > 
> > > Or perhaps we wait to hear about this causing a problem, and deal
> > > with
> > > it then? :)
> > > 
> > 
> > Yeah - I don't know what people want here. Clearly, we can't leave
> > kallsyms the way it is. Removing it entirely is a pretty fast way to
> > figure out how people use it though :).
> 
> Kexec-tools and makedumpfile are the users of /proc/kallsyms currently. 
> We use kallsyms to get page_offset_base and _stext.

AIUI, those run as root so they'd be able to consume the uncensored
output.

-- 
Kees Cook