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Re: [Xen-devel] x86: PIE support and option to extend KASLR randomization
- To: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
- From: Thomas Garnier <thgarnie@xxxxxxxxxx>
- Date: Mon, 21 Aug 2017 08:57:58 -0700
- Cc: Nicolas Pitre <nicolas.pitre@xxxxxxxxxx>, Michal Hocko <mhocko@xxxxxxxx>, Len Brown <len.brown@xxxxxxxxx>, Radim Krčmář <rkrcmar@xxxxxxxxxx>, Catalin Marinas <catalin.marinas@xxxxxxx>, Christopher Li <sparse@xxxxxxxxxxx>, Alexei Starovoitov <ast@xxxxxxxxxx>, David Howells <dhowells@xxxxxxxxxx>, Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>, Pavel Machek <pavel@xxxxxx>, "H . Peter Anvin" <hpa@xxxxxxxxx>, Kernel Hardening <kernel-hardening@xxxxxxxxxxxxxxxxxx>, Christoph Lameter <cl@xxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Kees Cook <keescook@xxxxxxxxxxxx>, the arch/x86 maintainers <x86@xxxxxxxxxx>, Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>, Daniel Borkmann <daniel@xxxxxxxxxxxxx>, Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>, Peter Foley <pefoley2@xxxxxxxxxxx>, Joerg Roedel <joro@xxxxxxxxxx>, "Rafael J . Wysocki" <rafael.j.wysocki@xxxxxxxxx>, Daniel Micay <danielmicay@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, linux-sparse@xxxxxxxxxxxxxxx, Matthias Kaehlcke <mka@xxxxxxxxxxxx>, linux-arch <linux-arch@xxxxxxxxxxxxxxx>, Waiman Long <longman@xxxxxxxxxx>, Borislav Petkov <bp@xxxxxxx>, Markus Trippelsdorf <markus@xxxxxxxxxxxxxxx>, Tom Lendacky <thomas.lendacky@xxxxxxx>, Rik van Riel <riel@xxxxxxxxxx>, Chris Metcalf <cmetcalf@xxxxxxxxxxxx>, Arnd Bergmann <arnd@xxxxxxxx>, Linux PM list <linux-pm@xxxxxxxxxxxxxxx>, Brian Gerst <brgerst@xxxxxxxxx>, "H . J . Lu" <hjl.tools@xxxxxxxxx>, Steven Rostedt <rostedt@xxxxxxxxxxx>, Borislav Petkov <bp@xxxxxxxxx>, Andy Lutomirski <luto@xxxxxxxxxx>, Josh Poimboeuf <jpoimboe@xxxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Dou Liyang <douly.fnst@xxxxxxxxxxxxxx>, Paul Bolle <pebolle@xxxxxxxxxx>, "Paul E . McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>, Baoquan He <bhe@xxxxxxxxxx>, Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, kvm list <kvm@xxxxxxxxxxxxxxx>, Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>, "Rafael J . Wysocki" <rjw@xxxxxxxxxxxxx>, LKML <linux-kernel@xxxxxxxxxxxxxxx>, Kyle Huey <me@xxxxxxxxxxxx>, Lukas Wunner <lukas@xxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Linux Crypto Mailing List <linux-crypto@xxxxxxxxxxxxxxx>, Rob Landley <rob@xxxxxxxxxxx>, Tejun Heo <tj@xxxxxxxxxx>, Paolo Bonzini <pbonzini@xxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>, "David S . Miller" <davem@xxxxxxxxxxxxx>, "Kirill A . Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
- Delivery-date: Mon, 21 Aug 2017 15:58:07 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
On Mon, Aug 21, 2017 at 7:31 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> On Tue, Aug 15, 2017 at 07:20:38AM -0700, Thomas Garnier wrote:
>> On Tue, Aug 15, 2017 at 12:56 AM, Ingo Molnar <mingo@xxxxxxxxxx> wrote:
>
>> > Have you considered a kernel with -mcmodel=small (or medium) instead of
>> > -fpie
>> > -mcmodel=large? We can pick a random 2GB window in the (non-kernel)
>> > canonical
>> > x86-64 address space to randomize the location of kernel text. The
>> > location of
>> > modules can be further randomized within that 2GB window.
>>
>> -model=small/medium assume you are on the low 32-bit. It generates
>> instructions where the virtual addresses have the high 32-bit to be
>> zero.
>
> That's a compiler fail, right? Because the SDM states that for "CALL
> rel32" the 32bit displacement is sign extended on x86_64.
>
That's different than what I expected at first too.
Now, I think I have an alternative of using mcmodel=large. I could use
-fPIC and ensure modules are never far away from the main kernel
(moving the module section start close to the random kernel end). I
looked at it and that seems possible but will require more work. I
plan to start with the mcmodel=large support and add this mode in a
way that could benefit classic KASLR (without -fPIC) because it
randomize where modules start based on the kernel.
--
Thomas
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