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Message-ID: <728a9499-67e9-0828-bb7a-f9b441a220b5@zytor.com>
Date: Sun, 27 Aug 2017 18:26:05 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Peter Zijlstra <peterz@...radead.org>,
Thomas Garnier <thgarnie@...gle.com>
Cc: Ingo Molnar <mingo@...nel.org>, Herbert Xu <herbert@...dor.apana.org.au>,
"David S . Miller" <davem@...emloft.net>,
Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.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>,
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Andrew Morton <akpm@...ux-foundation.org>,
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"H . J . Lu" <hjl.tools@...il.com>, Paul Bolle <pebolle@...cali.nl>,
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Daniel Micay <danielmicay@...il.com>,
the arch/x86 maintainers <x86@...nel.org>,
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Linus Torvalds <torvalds@...ux-foundation.org>,
Borislav Petkov <bp@...en8.de>
Subject: Re: x86: PIE support and option to extend KASLR randomization
On 08/21/17 07:31, Peter Zijlstra 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@...nel.org> 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.
>
No. It is about whether you can do something like:
movl $variable, %eax /* rax = &variable; */
or
addl %ecx,variable(,%rsi,4) /* variable[rsi] += ecx */
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