Date: Tue, 12 Dec 2017 19:05:09 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Andy Lutomirski <luto@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.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>, aliguori@amazon.com,
        Will Deacon <will.deacon@arm.com>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>
Subject: Re: [patch 05/16] mm: Allow special mappings with user access cleared
Message-ID: <20171212180509.iewpmzdhvsusk2nk@hirez.programming.kicks-ass.net>
References: <20171212173221.496222173@linutronix.de>
 <20171212173333.669577588@linutronix.de>
 <CALCETrXLeGGw+g7GiGDmReXgOxjB-cjmehdryOsFK4JB5BJAFQ@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CALCETrXLeGGw+g7GiGDmReXgOxjB-cjmehdryOsFK4JB5BJAFQ@mail.gmail.com>
User-Agent: NeoMutt/20170609 (1.8.3)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 774
Lines: 17

On Tue, Dec 12, 2017 at 10:00:08AM -0800, Andy Lutomirski wrote:
> On Tue, Dec 12, 2017 at 9:32 AM, Thomas Gleixner <tglx@linutronix.de> wrote:
> > From: Peter Zijstra <peterz@infradead.org>
> >
> > In order to create VMAs that are not accessible to userspace create a new
> > VM_NOUSER flag. This can be used in conjunction with
> > install_special_mapping() to inject 'kernel' data into the userspace map.
> >
> > Similar to how arch_vm_get_page_prot() allows adding _PAGE_flags to
> > pgprot_t, introduce arch_vm_get_page_prot_excl() which masks
> > _PAGE_flags from pgprot_t and use this to implement VM_NOUSER for x86.
> 
> How does this interact with get_user_pages(), etc?

gup would find the page. These patches do in fact rely on that through
the populate things.