linux-kernel - Re: [PATCH 24/30] x86, kaiser: disable native VSYSCALL

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Date:   Thu, 9 Nov 2017 22:31:30 -0800
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        moritz.lipp@...k.tugraz.at,
        Daniel Gruss <daniel.gruss@...k.tugraz.at>,
        michael.schwarz@...k.tugraz.at, richard.fellner@...dent.tugraz.at,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Kees Cook <keescook@...gle.com>,
        Hugh Dickins <hughd@...gle.com>, X86 ML <x86@...nel.org>
Subject: Re: [PATCH 24/30] x86, kaiser: disable native VSYSCALL

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.