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Date: Wed, 1 Nov 2017 09:06:42 +0100
From: Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH 12/23] x86, kaiser: map dynamically-allocated LDTs
Message-ID: <20171101080642.6rvmrt3ec6d27zki@gmail.com>
References: <20171031223146.6B47C861@viggo.jf.intel.com>
 <20171031223208.F271E813@viggo.jf.intel.com>
 <CALCETrVbGHJUeZP2X36s-gUcEywpv_uuAwZRVAJWL5U8DijPkQ@mail.gmail.com>
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To: Andy Lutomirski <luto@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>, "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@iaik.tugraz.at, michael.schwarz@iaik.tugraz.at, Linus Torvalds <torvalds@linux-foundation.org>, Kees Cook <keescook@google.com>, Hugh Dickins <hughd@google.com>, X86 ML <x86@kernel.org>


* Andy Lutomirski <luto@kernel.org> wrote:

> On Tue, Oct 31, 2017 at 3:32 PM, Dave Hansen
> <dave.hansen@linux.intel.com> wrote:
> >
> > Normally, a process just has a NULL mm->context.ldt.  But, we
> > have a syscall for a process to set a new one.  If a process does
> > that, we need to map the new LDT.
> >
> > The original KAISER patch missed this case.
> 
> Tglx suggested that we instead increase the padding at the top of the
> user address space from 4k to 64k and put the LDT there.  This is a
> slight ABI break, but I'd be rather surprised if anything noticed,
> especially because the randomized vdso currently regularly lands there
> (IIRC), so any user code that explicitly uses those 60k already
> collides with the vdso.
> 
> I can make this happen.

Yes, let's try that.

Thanks,

	Ingo

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