linux-kernel - Re: [PATCH v2 9/9] module: Reorder functions

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Message-ID: <fe529a4479b90d609937c10efb27394feda384a4.camel@linux.intel.com>
Date:   Tue, 09 Jun 2020 13:59:23 -0700
From:   Kristen Carlson Accardi <kristen@...ux.intel.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, Jessica Yu <jeyu@...nel.org>,
        arjan@...ux.intel.com, linux-kernel@...r.kernel.org,
        kernel-hardening@...ts.openwall.com, rick.p.edgecombe@...el.com,
        Ard Biesheuvel <ardb@...nel.org>,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH v2 9/9] module: Reorder functions

On Tue, 2020-06-09 at 13:42 -0700, Kees Cook wrote:
> On Tue, Jun 09, 2020 at 01:14:04PM -0700, Kristen Carlson Accardi
> wrote:
> > On Thu, 2020-05-21 at 14:33 -0700, Kees Cook wrote:
> > > Oh! And I am reminded suddenly about CONFIG_FG_KASLR needing to
> > > interact
> > > correctly with CONFIG_LD_DEAD_CODE_DATA_ELIMINATION in that we do
> > > NOT
> > > want the sections to be collapsed at link time:
> > 
> > sorry - I'm a little confused and was wondering if you could
> > clarify
> > something. Does this mean you expect CONFIG_FG_KASLR=y and
> > CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=y to be a valid config? I am
> > not
> 
> Yes, I don't see a reason they can't be used together.
> 
> > familiar with the option, but it seems like you are saying that it
> > requires sections to be collapsed, in which case both of these
> > options
> > as yes would not be allowed? Should I actively prevent this in the
> > Kconfig?
> 
> No, I'm saying that CONFIG_LD_DEAD_CODE_DATA_ELIMINATION does _not_
> actually require that the sections be collapsed, but the Makefile
> currently does this just to keep the resulting ELF "tidy". We want
> that disabled (for the .text parts) in the case of CONFIG_FG_KASLR.
> The
> dead code elimination step, is, IIUC, done at link time before the
> output sections are written.
> 

Ah ok, that makes sense. Thanks.