From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <owner-linux-mm@kvack.org>
Received: from mail-pf0-f198.google.com (mail-pf0-f198.google.com [209.85.192.198])
	by kanga.kvack.org (Postfix) with ESMTP id 79E826B0003
	for <linux-mm@kvack.org>; Wed, 11 Jul 2018 12:11:32 -0400 (EDT)
Received: by mail-pf0-f198.google.com with SMTP id f9-v6so15442232pfn.22
        for <linux-mm@kvack.org>; Wed, 11 Jul 2018 09:11:32 -0700 (PDT)
Received: from mga12.intel.com (mga12.intel.com. [192.55.52.136])
        by mx.google.com with ESMTPS id 34-v6si19074207pgs.243.2018.07.11.09.11.31
        for <linux-mm@kvack.org>
        (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128);
        Wed, 11 Jul 2018 09:11:31 -0700 (PDT)
Message-ID: <1531325272.13297.27.camel@intel.com>
Subject: Re: [RFC PATCH v2 15/27] mm/mprotect: Prevent mprotect from
 changing shadow stack
From: Yu-cheng Yu <yu-cheng.yu@intel.com>
Date: Wed, 11 Jul 2018 09:07:52 -0700
In-Reply-To: <20180711091232.GU2476@hirez.programming.kicks-ass.net>
References: <20180710222639.8241-1-yu-cheng.yu@intel.com>
	 <20180710222639.8241-16-yu-cheng.yu@intel.com>
	 <04800c52-1f86-c485-ba7c-2216d8c4966f@linux.intel.com>
	 <20180711091232.GU2476@hirez.programming.kicks-ass.net>
Content-Type: text/plain; charset="UTF-8"
Mime-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: owner-linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>
To: Peter Zijlstra <peterz@infradead.org>, Dave Hansen <dave.hansen@linux.intel.com>
Cc: x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>, Andy Lutomirski <luto@amacapital.net>, Balbir Singh <bsingharora@gmail.com>, Cyrill Gorcunov <gorcunov@gmail.com>, Florian Weimer <fweimer@redhat.com>, "H.J. Lu" <hjl.tools@gmail.com>, Jann Horn <jannh@google.com>, Jonathan Corbet <corbet@lwn.net>, Kees Cook <keescook@chromiun.org>, Mike Kravetz <mike.kravetz@oracle.com>, Nadav Amit <nadav.amit@gmail.com>, Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>, "Ravi V. Shankar" <ravi.v.shankar@intel.com>, Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com>

On Wed, 2018-07-11 at 11:12 +0200, Peter Zijlstra wrote:
> On Tue, Jul 10, 2018 at 04:10:08PM -0700, Dave Hansen wrote:
> > 
> > On 07/10/2018 03:26 PM, Yu-cheng Yu wrote:
> > > 
> > > Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
> > This still needs a changelog, even if you think it's simple.
> > > 
> > > --- a/mm/mprotect.c
> > > +++ b/mm/mprotect.c
> > > @@ -446,6 +446,15 @@ static int do_mprotect_pkey(unsigned long
> > > start, size_t len,
> > > A 	error = -ENOMEM;
> > > A 	if (!vma)
> > > A 		goto out;
> > > +
> > > +	/*
> > > +	A * Do not allow changing shadow stack memory.
> > > +	A */
> > > +	if (vma->vm_flags & VM_SHSTK) {
> > > +		error = -EINVAL;
> > > +		goto out;
> > > +	}
> > > +
> > I think this is a _bit_ draconian.A A Why shouldn't we be able to use
> > protection keys with a shadow stack?A A Or, set it to PROT_NONE?
> Right, and then there's also madvise() and some of the other
> accessors.
> 
> Why do we need to disallow this? AFAICT the worst that can happen is
> that a process wrecks itself, so what?

Agree. A I will remove the patch.