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

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Message-ID: <20200228033648.GJ24216@MiWiFi-R3L-srv>
Date:   Fri, 28 Feb 2020 11:36:48 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Kees Cook <keescook@...omium.org>
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 02/27/20 at 08:02am, Kees Cook wrote:
> 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.

Yes, they have to be run under root.