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Subject: Re: [PATCH 24/30] x86, kaiser: disable native VSYSCALL
References: <20171108194646.907A1942@viggo.jf.intel.com>
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From: Dave Hansen <dave.hansen@linux.intel.com>
Message-ID: <27b55108-1e72-cb3d-d5d8-ffe0238245aa@linux.intel.com>
Date: Thu, 9 Nov 2017 16:57:45 -0800
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To: Andy Lutomirski <luto@kernel.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>, moritz.lipp@iaik.tugraz.at, Daniel Gruss <daniel.gruss@iaik.tugraz.at>, michael.schwarz@iaik.tugraz.at, richard.fellner@student.tugraz.at, Linus Torvalds <torvalds@linux-foundation.org>, Kees Cook <keescook@google.com>, Hugh Dickins <hughd@google.com>, X86 ML <x86@kernel.org>

On 11/09/2017 04:53 PM, Andy Lutomirski wrote:
>> The KAISER code attempts to "poison" the user portion of the kernel page
>> tables.  It detects the entries pages that it wants that it wants to
>> poison in two ways:
>>  * Looking for addresses >= PAGE_OFFSET
>>  * Looking for entries without _PAGE_USER set
> What do you mean "poison"?

I meant the _PAGE_NX magic that we do in here:

https://git.kernel.org/pub/scm/linux/kernel/git/daveh/x86-kaiser.git/commit/?h=kaiser-414rc7-20171108&id=c4f7d0819170761f092fcf2327b85b082368e73a

to ensure that userspace is unable to run on the kernel PGD.

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