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Date: Thu, 14 Dec 2017 23:23:55 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH v2 11/17] selftests/x86/ldt_gdt: Prepare for access bit
 forced
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References: <20171214112726.742649793@infradead.org> <20171214113851.647809433@infradead.org> <CALCETrW0=FnqZMU_MLebyy5m7jj=w=yHYx=u6vghFkdmG7vsww@mail.gmail.com> <CA+55aFz71Ycm3oez30zOCztx1sio8ioy3VED2rE0ORoExXBz2g@mail.gmail.com>
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To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>, Peter Zijlstra <peterz@infradead.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>, Dave Hansen <dave.hansen@intel.com>, Borislav Petkov <bpetkov@suse.de>, Greg KH <gregkh@linuxfoundation.org>, Kees Cook <keescook@google.com>, Hugh Dickins <hughd@google.com>, Brian Gerst <brgerst@gmail.com>, Josh Poimboeuf <jpoimboe@redhat.com>, Denys Vlasenko <dvlasenk@redhat.com>, Boris Ostrovsky <boris.ostrovsky@oracle.com>, Juergen Gross <jgross@suse.com>, David Laight <David.Laight@aculab.com>, Eduardo Valentin <eduval@amazon.com>, "Liguori, Anthony" <aliguori@amazon.com>, Will Deacon <will.deacon@arm.com>, "linux-mm@kvack.org" <linux-mm@kvack.org>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Dan Williams <dan.j.williams@intel.com>

On Thu, 14 Dec 2017, Linus Torvalds wrote:

> On Thu, Dec 14, 2017 at 1:22 PM, Andy Lutomirski <luto@kernel.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


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