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Date:   Tue, 6 Aug 2019 17:50:34 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Borislav Petkov <bp@alien8.de>
Cc:     Thomas Garnier <thgarnie@chromium.org>,
        kernel-hardening@lists.openwall.com, kristen@linux.intel.com,
        keescook@chromium.org, Herbert Xu <herbert@gondor.apana.org.au>,
        "David S. Miller" <davem@davemloft.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org,
        Andy Lutomirski <luto@kernel.org>,
        Juergen Gross <jgross@suse.com>,
        Thomas Hellstrom <thellstrom@vmware.com>,
        "VMware, Inc." <pv-drivers@vmware.com>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Len Brown <len.brown@intel.com>, Pavel Machek <pavel@ucw.cz>,
        Nadav Amit <namit@vmware.com>, Jann Horn <jannh@google.com>,
        Feng Tang <feng.tang@intel.com>,
        Maran Wilson <maran.wilson@oracle.com>,
        Enrico Weigelt <info@metux.net>,
        Allison Randal <allison@lohutok.net>,
        Alexios Zavras <alexios.zavras@intel.com>,
        linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org,
        virtualization@lists.linux-foundation.org, linux-pm@vger.kernel.org
Subject: Re: [PATCH v9 00/11] x86: PIE support to extend KASLR randomization
Message-ID: <20190806155034.GP2349@hirez.programming.kicks-ass.net>
References: <20190730191303.206365-1-thgarnie@chromium.org>
 <20190806154347.GD25897@zn.tnic>
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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.