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Date:   Thu, 27 Feb 2020 08:02:37 -0800
From:   Kees Cook <keescook@chromium.org>
To:     Baoquan He <bhe@redhat.com>
Cc:     Kristen Carlson Accardi <kristen@linux.intel.com>,
        dyoung@redhat.com, tglx@linutronix.de, mingo@redhat.com,
        bp@alien8.de, hpa@zytor.com, arjan@linux.intel.com,
        rick.p.edgecombe@intel.com, x86@kernel.org,
        linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com,
        kexec@lists.infradead.org
Subject: Re: [RFC PATCH 09/11] kallsyms: hide layout and expose seed
Message-ID: <202002270802.1CA8B32AC@keescook>
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 <202002060428.08B14F1@keescook>
 <a915e1eb131551aa766fde4c14de5a3e825af667.camel@linux.intel.com>
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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