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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: <f5483db4-018c-3474-0819-65336cacdb1d@linux.intel.com>
Date: Thu, 9 Nov 2017 22:31:30 -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 06:25 PM, Andy Lutomirski wrote:
> Here are two proposals to address this without breaking vsyscalls.
> 
> 1. Set NX on low mappings that are _PAGE_USER.  Don't set NX on high
> mappings but, optionally, warn if you see _PAGE_USER on any address
> that isn't the vsyscall page.
> 
> 2. Ignore _PAGE_USER entirely and just mark the EFI mm as special so
> KAISER doesn't muck with it.

These are totally doable.  But, what's the big deal with breaking native
vsyscall?  We can still do the emulation so nothing breaks: it is just slow.

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