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Message-ID: <301c7fb7d22ad6ef97856b421873e32c2239d412.camel@linux.intel.com>
Subject: Re: [PATCH v4 00/10] Function Granular KASLR
From:   Kristen Carlson Accardi <kristen@linux.intel.com>
To:     Kees Cook <keescook@chromium.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>
Cc:     Miroslav Benes <mbenes@suse.cz>, 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
Date:   Wed, 22 Jul 2020 12:56:10 -0700
In-Reply-To: <202007221241.EBC2215A@keescook>
References: <20200717170008.5949-1-kristen@linux.intel.com>
         <alpine.LSU.2.21.2007221122110.10163@pobox.suse.cz>
         <202007220738.72F26D2480@keescook> <20200722160730.cfhcj4eisglnzolr@treble>
         <202007221241.EBC2215A@keescook>
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On Wed, 2020-07-22 at 12:42 -0700, Kees Cook wrote:
> 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.
> 

Well, glad to hear there might be some precendence for how to solve
this, as I wasn't able to think of something reasonable off the top of
my head. Are you speaking of the Clang LTO series? 
https://lore.kernel.org/lkml/20200624203200.78870-1-samitolvanen@google.com/