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Re: [Xen-devel] [RFC 21/22] x86/module: Add support for mcmodel large and PLTs
- To: Thomas Garnier <thgarnie@xxxxxxxxxx>, Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>, "David S . Miller" <davem@xxxxxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Josh Poimboeuf <jpoimboe@xxxxxxxxxx>, Arnd Bergmann <arnd@xxxxxxxx>, Matthias Kaehlcke <mka@xxxxxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Paolo Bonzini <pbonzini@xxxxxxxxxx>, Radim Krčmář <rkrcmar@xxxxxxxxxx>, Joerg Roedel <joro@xxxxxxxxxx>, Andy Lutomirski <luto@xxxxxxxxxx>, Borislav Petkov <bp@xxxxxxxxx>, "Kirill A . Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>, Brian Gerst <brgerst@xxxxxxxxx>, Borislav Petkov <bp@xxxxxxx>, Christian Borntraeger <borntraeger@xxxxxxxxxx>, "Rafael J . Wysocki" <rjw@xxxxxxxxxxxxx>, Len Brown <len.brown@xxxxxxxxx>, Pavel Machek <pavel@xxxxxx>, Tejun Heo <tj@xxxxxxxxxx>, Christoph Lameter <cl@xxxxxxxxx>, Kees Cook <keescook@xxxxxxxxxxxx>, Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>, Chris Metcalf <cmetcalf@xxxxxxxxxxxx>, "Paul E . McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Christopher Li <sparse@xxxxxxxxxxx>, Dou Liyang <douly.fnst@xxxxxxxxxxxxxx>, Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>, Daniel Borkmann <daniel@xxxxxxxxxxxxx>, Markus Trippelsdorf <markus@xxxxxxxxxxxxxxx>, Peter Foley <pefoley2@xxxxxxxxxxx>, Steven Rostedt <rostedt@xxxxxxxxxxx>, Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>, Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>, Catalin Marinas <catalin.marinas@xxxxxxx>, Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>, Michal Hocko <mhocko@xxxxxxxx>, Rob Landley <rob@xxxxxxxxxxx>, Jiri Kosina <jkosina@xxxxxxx>, "H . J . Lu" <hjl.tools@xxxxxxxxx>, Paul Bolle <pebolle@xxxxxxxxxx>, Baoquan He <bhe@xxxxxxxxxx>, Daniel Micay <danielmicay@xxxxxxxxx>
- From: "H. Peter Anvin" <hpa@xxxxxxxxx>
- Date: Tue, 18 Jul 2017 18:35:05 -0700
- Cc: linux-arch@xxxxxxxxxxxxxxx, kvm@xxxxxxxxxxxxxxx, linux-pm@xxxxxxxxxxxxxxx, x86@xxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, linux-sparse@xxxxxxxxxxxxxxx, linux-crypto@xxxxxxxxxxxxxxx, kernel-hardening@xxxxxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Wed, 19 Jul 2017 02:00:06 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
On 07/18/17 15:33, Thomas Garnier wrote:
> With PIE support and KASLR extended range, the modules may be further
> away from the kernel than before breaking mcmodel=kernel expectations.
>
> Add an option to build modules with mcmodel=large. The modules generated
> code will make no assumptions on placement in memory.
>
> Despite this option, modules still expect kernel functions to be within
> 2G and generate relative calls. To solve this issue, the PLT arm64 code
> was adapted for x86_64. When a relative relocation go outside its range,
> a dynamic PLT entry is used to correctly jump to the destination.
Why large as opposed to medium or medium-PIC?
-hpa
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