linux-kernel - Re: [PATCH v4 00/10] Function Granular KASLR

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Date:   Mon, 3 Aug 2020 17:12:28 -0400
From:   "Frank Ch. Eigler" <fche@...hat.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Joe Lawrence <joe.lawrence@...hat.com>,
        Evgenii Shatokhin <eshatokhin@...tuozzo.com>,
        Kristen Carlson Accardi <kristen@...ux.intel.com>,
        Miroslav Benes <mbenes@...e.cz>, 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,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jessica Yu <jeyu@...nel.org>
Subject: Re: [PATCH v4 00/10] Function Granular KASLR

Hi -

On Mon, Aug 03, 2020 at 01:11:27PM -0700, Kees Cook wrote:
> [...]
> > Systemtap needs to know base addresses of loaded text & data sections,
> > in order to perform relocation of probe point PCs and context data
> > addresses.  It uses /sys/module/...., kind of under protest, because
> > there seems to exist no MODULE_EXPORT'd API to get at that information
> > some other way.
> 
> Wouldn't /proc/kallsysms entries cover this? I must be missing
> something...

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.

- FChE