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Re: [Xen-devel] x86: PIE support and option to extend KASLR randomization
- To: Ingo Molnar <mingo@xxxxxxxxxx>
- From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
- Date: Mon, 21 Aug 2017 15:32:22 +0200
- 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>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, 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>, "David S . Miller" <davem@xxxxxxxxxxxxx>, Kyle Huey <me@xxxxxxxxxxxx>, Lukas Wunner <lukas@xxxxxxxxx>, 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>, Thomas Garnier <thgarnie@xxxxxxxxxx>, "Kirill A . Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
- Delivery-date: Mon, 21 Aug 2017 13:33:41 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
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 ?
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