Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Mon, 3 Aug 2020 20:48:17 -0400
From:   "Frank Ch. Eigler" <fche@redhat.com>
To:     Kees Cook <keescook@chromium.org>
Cc:     Joe Lawrence <joe.lawrence@redhat.com>,
        Evgenii Shatokhin <eshatokhin@virtuozzo.com>,
        Kristen Carlson Accardi <kristen@linux.intel.com>,
        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,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Jessica Yu <jeyu@kernel.org>
Subject: Re: [PATCH v4 00/10] Function Granular KASLR
Message-ID: <20200804004817.GD30810@redhat.com>
References: <20200717170008.5949-1-kristen@linux.intel.com>
 <alpine.LSU.2.21.2007221122110.10163@pobox.suse.cz>
 <e9c4d88b-86db-47e9-4299-3fac45a7e3fd@virtuozzo.com>
 <202008031043.FE182E9@keescook>
 <fc6d2289-af97-5cf8-a4bb-77c2b0b8375c@redhat.com>
 <20200803193837.GB30810@redhat.com>
 <202008031310.4F8DAA20@keescook>
 <20200803211228.GC30810@redhat.com>
 <202008031439.F1399A588@keescook>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <202008031439.F1399A588@keescook>
User-Agent: Mutt/1.12.0 (2019-05-25)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Hi -

> > We have relocated based on sections, not some subset of function
> > symbols accessible that way, partly because DWARF line- and DIE- based
> > probes can map to addresses some way away from function symbols, into
> > function interiors, or cloned/moved bits of optimized code.  It would
> > take some work to prove that function-symbol based heuristic
> > arithmetic would have just as much reach.
> 
> Interesting. Do you have an example handy? 

No, I'm afraid I don't have one that I know cannot possibly be
expressed by reference to a function symbol only.  I'd look at
systemtap (4.3) probe point lists like:

% stap -vL 'kernel.statement("*@kernel/*verif*.c:*")'
% stap -vL 'module("amdgpu").statement("*@*execution*.c:*")'

which give an impression of computed PC addresses.

> It seems like something like that would reference the enclosing
> section, which means we can't just leave them out of the sysfs
> list... (but if such things never happen in the function-sections,
> then we *can* remove them...)

I'm not sure we can easily prove they can never happen there.

- FChE