linux-kernel - Re: [PATCH v2 0/9] Function Granular KASLR

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Message-ID: <87tv08svl8.fsf@nanos.tec.linutronix.de>
Date:   Fri, 22 May 2020 01:43:15 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Kees Cook <keescook@...omium.org>
Cc:     Kristen Carlson Accardi <kristen@...ux.intel.com>,
        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
Subject: Re: [PATCH v2 0/9] Function Granular KASLR

Kees,

Kees Cook <keescook@...omium.org> writes:
> On Fri, May 22, 2020 at 12:26:30AM +0200, Thomas Gleixner wrote:
>> I understand how this is supposed to work, but I fail to find an
>> explanation how all of this is preserving the text subsections we have,
>> i.e. .kprobes.text, .entry.text ...?
>
> I had the same question when I first started looking at earlier versions
> of this series! :)
>
>> I assume that the functions in these subsections are reshuffled within
>> their own randomized address space so that __xxx_text_start and
>> __xxx_text_end markers still make sense, right?
>
> No, but perhaps in the future. Right now, they are entirely ignored and
> left untouched.

I'm fine with that restriction, but for a moment I got worried that this
might screw up explicit subsections.

This really want's to be clearly expressed in the cover letter and the
changelogs so that such questions don't arise again.

<SNIP>

> So, before any of that, just .text.* is a good first step, and after
> that I think next would be getting .text randomized relative to the other
> .text.* sections (IIUC, it is entirely untouched currently, so only the
> standard KASLR base offset moves it around). Only after that do we start
> poking around trying to munge the special section contents (which
> requires use solving a few problems simultaneously). :)

Thanks for the detailed explanation!

       tglx