[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20170821142854.dmuusnbc2tsrai3v@hirez.programming.kicks-ass.net>
Date: Mon, 21 Aug 2017 16:28:54 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Ingo Molnar <mingo@...nel.org>
Cc: Thomas Garnier <thgarnie@...gle.com>,
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>,
Josh Poimboeuf <jpoimboe@...hat.com>, Arnd Bergmann <arnd@...db.de>,
Matthias Kaehlcke <mka@...omium.org>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Juergen Gross <jgross@...e.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Radim Krčmář <rkrcmar@...hat.com>,
Joerg Roedel <joro@...tes.org>,
Tom Lendacky <thomas.lendacky@....com>,
Andy Lutomirski <luto@...nel.org>, Borislav Petkov <bp@...e.de>,
Brian Gerst <brgerst@...il.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
"Rafael J . Wysocki" <rjw@...ysocki.net>,
Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>,
Paul Gortmaker <paul.gortmaker@...driver.com>,
Chris Metcalf <cmetcalf@...lanox.com>,
Andrew Morton <akpm@...ux-foundation.org>,
"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
Nicolas Pitre <nicolas.pitre@...aro.org>,
Christopher Li <sparse@...isli.org>,
"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
Lukas Wunner <lukas@...ner.de>,
Mika Westerberg <mika.westerberg@...ux.intel.com>,
Dou Liyang <douly.fnst@...fujitsu.com>,
Daniel Borkmann <daniel@...earbox.net>,
Alexei Starovoitov <ast@...nel.org>,
Masahiro Yamada <yamada.masahiro@...ionext.com>,
Markus Trippelsdorf <markus@...ppelsdorf.de>,
Steven Rostedt <rostedt@...dmis.org>,
Kees Cook <keescook@...omium.org>, Rik van Riel <riel@...hat.com>,
David Howells <dhowells@...hat.com>,
Waiman Long <longman@...hat.com>, Kyle Huey <me@...ehuey.com>,
Peter Foley <pefoley2@...oley.com>,
Tim Chen <tim.c.chen@...ux.intel.com>,
Catalin Marinas <catalin.marinas@....com>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Michal Hocko <mhocko@...e.com>,
Matthew Wilcox <mawilcox@...rosoft.com>,
"H . J . Lu" <hjl.tools@...il.com>, Paul Bolle <pebolle@...cali.nl>,
Rob Landley <rob@...dley.net>, Baoquan He <bhe@...hat.com>,
Daniel Micay <danielmicay@...il.com>,
the arch/x86 maintainers <x86@...nel.org>,
linux-crypto@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
xen-devel@...ts.xenproject.org, kvm list <kvm@...r.kernel.org>,
Linux PM list <linux-pm@...r.kernel.org>,
linux-arch <linux-arch@...r.kernel.org>,
linux-sparse@...r.kernel.org,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Borislav Petkov <bp@...en8.de>
Subject: Re: x86: PIE support and option to extend KASLR randomization
On Mon, Aug 21, 2017 at 03:32:22PM +0200, Peter Zijlstra wrote:
> On Wed, Aug 16, 2017 at 05:12:35PM +0200, Ingo Molnar wrote:
> > Unfortunately mcmodel=large looks pretty heavy too AFAICS, at the machine
> > instruction level.
> >
> > Function calls look like this:
> >
> > -mcmodel=medium:
> >
> > 757: e8 98 ff ff ff callq 6f4 <test_code>
> >
> > -mcmodel=large
> >
> > 77b: 48 b8 10 f7 df ff ff movabs $0xffffffffffdff710,%rax
> > 782: ff ff ff
> > 785: 48 8d 04 03 lea (%rbx,%rax,1),%rax
> > 789: ff d0 callq *%rax
> >
> > And we'd do this for _EVERY_ function call in the kernel. That kind of crap is
> > totally unacceptable.
>
> So why does this need to be computed for every single call? How often
> will we move the kernel around at runtime?
>
> Why can't we process the relocation at load time and then discard the
> relocation tables along with the rest of __init ?
Ah, I see, this is large mode and that needs to use MOVABS to load 64bit
immediates. Still, small RIP relative should be able to live at any
point as long as everything lives inside the same 2G relative range, so
would still allow the goal of increasing the KASLR range.
So I'm not seeing how we need large mode for that. That said, after
reading up on all this, RIP relative will not be too pretty either,
while CALL is naturally RIP relative, data still needs an explicit %rip
offset, still loads better than the large model.
Powered by blists - more mailing lists
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
