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Date:   Wed, 22 Jul 2020 12:42:50 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Josh Poimboeuf <jpoimboe@redhat.com>
Cc:     Miroslav Benes <mbenes@suse.cz>,
        Kristen Carlson Accardi <kristen@linux.intel.com>,
        tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
        arjan@linux.intel.com, x86@kernel.org,
        linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com,
        rick.p.edgecombe@intel.com, live-patching@vger.kernel.org
Subject: Re: [PATCH v4 00/10] Function Granular KASLR
Message-ID: <202007221241.EBC2215A@keescook>
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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