linux-kernel - Re: [PATCH v2 11/17] selftests/x86/ldt

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Date:   Thu, 14 Dec 2017 23:23:55 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
cc:     Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        X86 ML <x86@...nel.org>, Dave Hansen <dave.hansen@...el.com>,
        Borislav Petkov <bpetkov@...e.de>,
        Greg KH <gregkh@...uxfoundation.org>,
        Kees Cook <keescook@...gle.com>,
        Hugh Dickins <hughd@...gle.com>,
        Brian Gerst <brgerst@...il.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        David Laight <David.Laight@...lab.com>,
        Eduardo Valentin <eduval@...zon.com>,
        "Liguori, Anthony" <aliguori@...zon.com>,
        Will Deacon <will.deacon@....com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH v2 11/17] selftests/x86/ldt_gdt: Prepare for access bit
 forced

On Thu, 14 Dec 2017, Linus Torvalds wrote:

> On Thu, Dec 14, 2017 at 1:22 PM, Andy Lutomirski <luto@...nel.org> wrote:
> >
> > Which kind of kills the whole thing.  There's no way the idea of
> > putting the LDT in a VMA is okay if it's RW.
> 
> Sure there is.
> 
> I really don't understand why you guys think it has to be RO.
> 
> All it has to be is not _user_ accessible. And that's a requirement
> regardless, because no way in hell should users be able to read the
> damn thing.

The user knows the LDT contents because he put it there and it can be read
via modify_ldt(0, ) anyway. Or am I misunderstanding what you are trying to
say?

Thanks,

	tglx