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

From: Thomas Garnier <thgarnie@chromium.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>,
	Kristen Carlson Accardi <kristen@linux.intel.com>,
	Kees Cook <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>,
	"the arch/x86 maintainers" <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 Mailing List <linux-crypto@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	virtualization@lists.linux-foundation.org,
	Linux PM list <linux-pm@vger.kernel.org>
Subject: Re: [PATCH v9 00/11] x86: PIE support to extend KASLR randomization
Date: Fri, 6 Sep 2019 16:22:47 -0700	[thread overview]
Message-ID: <CAJcbSZEc07UJtWyM5i-DGRpNTtoxoY7cDpdyDh3N-Bb+G3s0gA@mail.gmail.com> (raw)
In-Reply-To: <CAJcbSZETvvQYmh6U_Oauptdsrp-emmSG_QsAZzKLv+0-b2Yxig@mail.gmail.com>

On Thu, Aug 29, 2019 at 12:55 PM Thomas Garnier <thgarnie@chromium.org> wrote:
>
> On Tue, Aug 6, 2019 at 8:51 AM Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > 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.
>
> The goal is being able to extend the range of addresses where the
> kernel can be placed with KASLR. I will look at clarifying that in the
> future.
>
> >
> > 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.
> >
>
> I will look into that as well.

Following a discussion with Kees. I will explore objtool in the
follow-up patchset as we still have more elaborate pie changes in the
second set. I like the idea overall and I think it would be great if
it works.