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Date: Thu, 9 Aug 2018 13:16:03 +0200
From: Joerg Roedel <jroedel@suse.de>
Subject: Re: [PATCH] x86/mm/pti: Move user W+X check into pti_finalize()
Message-ID: <20180809111603.aqon7xqmanvoycbu@suse.de>
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 <aee38579-3a53-3370-b22b-04603b6b65ce@intel.com>
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To: Dave Hansen <dave.hansen@intel.com>
Cc: Joerg Roedel <joro@8bytes.org>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>, "H . Peter Anvin" <hpa@zytor.com>, x86@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Linus Torvalds <torvalds@linux-foundation.org>, Andy Lutomirski <luto@kernel.org>, Josh Poimboeuf <jpoimboe@redhat.com>, Juergen Gross <jgross@suse.com>, Peter Zijlstra <peterz@infradead.org>, Borislav Petkov <bp@alien8.de>, Jiri Kosina <jkosina@suse.cz>, Boris Ostrovsky <boris.ostrovsky@oracle.com>, Brian Gerst <brgerst@gmail.com>, David Laight <David.Laight@aculab.com>, Denys Vlasenko <dvlasenk@redhat.com>, Eduardo Valentin <eduval@amazon.com>, Greg KH <gregkh@linuxfoundation.org>, Will Deacon <will.deacon@arm.com>, aliguori@amazon.com, daniel.gruss@iaik.tugraz.at, hughd@google.com, keescook@google.com, Andrea Arcangeli <aarcange@redhat.com>, Waiman Long <llong@redhat.com>, Pavel Machek <pavel@ucw.cz>, "David H . Gutteridge" <dhgutteridge@sympatico.ca>

Hi Dave,

On Wed, Aug 08, 2018 at 08:54:37AM -0700, Dave Hansen wrote:
> One bit of information missing from the changelog: Could you clarify how
> there are any entries in the user page tables for the code to complain?
> Before pti_init(), I would have expected the user page tables to be empty.

The W+X check runs at the end of mark_readonly() in x86, which is after
pti_init() already put kernel mappings into the user page-table. Problem
is that the cloned entries are still W+X mapped, which is fixed in
pti_finalize() running _after_ mark_readonly().

Regards,

	Joerg