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

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Date:   Mon, 20 Apr 2020 15:43:21 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Arjan van de Ven <arjan@...ux.intel.com>
Cc:     Kristen Carlson Accardi <kristen@...ux.intel.com>,
        Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        hpa@...or.com, Jessica Yu <jeyu@...nel.org>,
        X86 ML <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        kernel-hardening@...ts.openwall.com, rick.p.edgecomb@...el.com
Subject: Re: [PATCH 9/9] module: Reorder functions

On Mon, 20 Apr 2020 at 15:37, Arjan van de Ven <arjan@...ux.intel.com> wrote:
>
> On 4/20/2020 5:01 AM, Ard Biesheuvel wrote:
> > Is that the only prerequisite? I.e., is it sufficient for another
> > architecture to add -ffunction-sections to the module CFLAGS to get
> > this functionality? (assuming it defines CONFIG_FG_KASLR=y)
>
> I suspect you also need/want at least normal KASLR enabled as
> a "does it even make sense" common sense threshold

Fair enough. But that is more of a policy concern than a functional concern.

FWIW I took patches #8 and #9, hardwired a couple of CONFIG_FG_KASLR=y
checks and added the -ffunction-sections GCC option for the modules,
and everything appears to be working as expected on arm64. I was just
wondering if I was missing something.

Note that arm64 does not have a decompressor, so there the fine
grained randomization of the core kernel is not really feasible using
the approach presented here.