linux-kernel - Re: [PATCH v9 00/11] x86: PIE support to extend KASLR randomization

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Message-ID: <20190806155034.GP2349@hirez.programming.kicks-ass.net>
Date:   Tue, 6 Aug 2019 17:50:34 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Thomas Garnier <thgarnie@...omium.org>,
        kernel-hardening@...ts.openwall.com, kristen@...ux.intel.com,
        keescook@...omium.org, Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        Juergen Gross <jgross@...e.com>,
        Thomas Hellstrom <thellstrom@...are.com>,
        "VMware, Inc." <pv-drivers@...are.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        Nadav Amit <namit@...are.com>, Jann Horn <jannh@...gle.com>,
        Feng Tang <feng.tang@...el.com>,
        Maran Wilson <maran.wilson@...cle.com>,
        Enrico Weigelt <info@...ux.net>,
        Allison Randal <allison@...utok.net>,
        Alexios Zavras <alexios.zavras@...el.com>,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH v9 00/11] x86: PIE support to extend KASLR randomization

On Tue, Aug 06, 2019 at 05:43:47PM +0200, Borislav Petkov wrote:
> On Tue, Jul 30, 2019 at 12:12:44PM -0700, Thomas Garnier wrote:
> > These patches make some of the changes necessary to build the kernel as
> > Position Independent Executable (PIE) on x86_64. Another patchset will
> > add the PIE option and larger architecture changes.
> 
> Yeah, about this: do we have a longer writeup about the actual benefits
> of all this and why we should take this all? After all, after looking
> at the first couple of asm patches, it is posing restrictions to how
> we deal with virtual addresses in asm (only RIP-relative addressing in
> 64-bit mode, MOVs with 64-bit immediates, etc, for example) and I'm
> willing to bet money that some future unrelated change will break PIE
> sooner or later.

Possibly objtool can help here; it should be possible to teach it about
these rules, and then it will yell when violated. That should avoid
regressions.