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Message-ID: <4dffd167-9cfd-dfcc-6556-05d7ca8f4595@linux.intel.com>
Date: Thu, 5 Jan 2017 07:08:05 -0800
From: Arjan van de Ven <arjan@...ux.intel.com>
To: Ingo Molnar <mingo@...nel.org>, Thomas Garnier <thgarnie@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
"H . Peter Anvin" <hpa@...or.com>, Kees Cook <keescook@...omium.org>,
Borislav Petkov <bp@...en8.de>, Andy Lutomirski <luto@...nel.org>,
Dave Hansen <dave@...1.net>, Chen Yucong <slaoub@...il.com>,
Paul Gortmaker <paul.gortmaker@...driver.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Masahiro Yamada <yamada.masahiro@...ionext.com>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Anna-Maria Gleixner <anna-maria@...utronix.de>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Rasmus Villemoes <linux@...musvillemoes.dk>,
Michael Ellerman <mpe@...erman.id.au>, Juergen Gross <jgross@...e.com>,
Richard Weinberger <richard@....at>, x86@...nel.org,
linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com,
Linus Torvalds <torvalds@...ux-foundation.org>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location
On 1/5/2017 12:11 AM, Ingo Molnar wrote:
>
> * Thomas Garnier <thgarnie@...gle.com> wrote:
>
>> Each processor holds a GDT in its per-cpu structure. The sgdt
>> instruction gives the base address of the current GDT. This address can
>> be used to bypass KASLR memory randomization. With another bug, an
>> attacker could target other per-cpu structures or deduce the base of the
>> main memory section (PAGE_OFFSET).
>>
>> In this change, a space is reserved at the end of the memory range
>> available for KASLR memory randomization. The space is big enough to hold
>> the maximum number of CPUs (as defined by setup_max_cpus). Each GDT is
>> mapped at specific offset based on the target CPU. Note that if there is
>> not enough space available, the GDTs are not remapped.
>>
>> The document was changed to mention GDT remapping for KASLR. This patch
>> also include dump page tables support.
>>
>> This patch was tested on multiple hardware configurations and for
>> hibernation support.
>
>> void kernel_randomize_memory(void);
>> +void kernel_randomize_smp(void);
>> +void* kaslr_get_gdt_remap(int cpu);
>
> Yeah, no fundamental objections from me to the principle, but I get some bad vibes
> from the naming here: seeing that kernel_randomize_smp() actually makes things
> less random.
>
kernel_unrandomize_smp() ...
one request.. can we make sure this unrandomization is optional?
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