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Message-ID: <202007221241.EBC2215A@keescook>
Date: Wed, 22 Jul 2020 12:42:50 -0700
From: Kees Cook <keescook@...omium.org>
To: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Miroslav Benes <mbenes@...e.cz>,
Kristen Carlson Accardi <kristen@...ux.intel.com>,
tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
arjan@...ux.intel.com, x86@...nel.org, linux-kernel@...r.kernel.org,
kernel-hardening@...ts.openwall.com, rick.p.edgecombe@...el.com,
live-patching@...r.kernel.org
Subject: Re: [PATCH v4 00/10] Function Granular KASLR
On Wed, Jul 22, 2020 at 11:07:30AM -0500, Josh Poimboeuf wrote:
> On Wed, Jul 22, 2020 at 07:39:55AM -0700, Kees Cook wrote:
> > On Wed, Jul 22, 2020 at 11:27:30AM +0200, Miroslav Benes wrote:
> > > Let me CC live-patching ML, because from a quick glance this is something
> > > which could impact live patching code. At least it invalidates assumptions
> > > which "sympos" is based on.
> >
> > In a quick skim, it looks like the symbol resolution is using
> > kallsyms_on_each_symbol(), so I think this is safe? What's a good
> > selftest for live-patching?
>
> The problem is duplicate symbols. If there are two static functions
> named 'foo' then livepatch needs a way to distinguish them.
>
> Our current approach to that problem is "sympos". We rely on the fact
> that the second foo() always comes after the first one in the symbol
> list and kallsyms. So they're referred to as foo,1 and foo,2.
Ah. Fun. In that case, perhaps the LTO series has some solutions. I
think builds with LTO end up renaming duplicate symbols like that, so
it'll be back to being unique.
--
Kees Cook
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