From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1758267AbcGKKM6 (ORCPT <rfc822;w@1wt.eu>);
	Mon, 11 Jul 2016 06:12:58 -0400
Received: from szxga02-in.huawei.com ([119.145.14.65]:53170 "EHLO
	szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1758218AbcGKKMx (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Mon, 11 Jul 2016 06:12:53 -0400
Message-ID: <5783710E.3070602@huawei.com>
Date: Mon, 11 Jul 2016 18:12:30 +0800
From: Xishi Qiu <qiuxishi@huawei.com>
User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:12.0) Gecko/20120428 Thunderbird/12.0.1
MIME-Version: 1.0
To: <alan@lxorguk.ukuu.org.uk>
CC: Linux MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>
Subject: a question about protection_map[]
Content-Type: text/plain; charset="ISO-8859-1"
Content-Transfer-Encoding: 7bit
X-Originating-IP: [10.177.25.179]
X-CFilter-Loop: Reflected
X-Mirapoint-Virus-RAPID-Raw: score=unknown(0),
	refid=str=0001.0A090204.57837117.001A,ss=1,re=0.000,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0,
	ip=0.0.0.0,
	so=2013-06-18 04:22:30,
	dmn=2013-03-21 17:37:32
X-Mirapoint-Loop-Id: e9b024b317ce8934c49506716f34b74a
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

Hi,

We can use mprotect to set read only or read/write.

mprotect_fixup()
	vma_set_page_prot()
		vm_pgprot_modify()
			vm_get_page_prot()
				protection_map[vm_flags & (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]

The following code shows that prots from __P001(PROT_READ) and __P010(PROT_WRITE)
are the same, so how does it distinguish read only or read/write from mprotect?

pgprot_t protection_map[16] = {
	__P000, __P001, __P010, __P011, __P100, __P101, __P110, __P111,
	__S000, __S001, __S010, __S011, __S100, __S101, __S110, __S111
};

#define __P001	PAGE_READONLY
#define __P010	PAGE_COPY

#define PAGE_READONLY		__pgprot(_PAGE_PRESENT | _PAGE_USER |	\
					 _PAGE_ACCESSED | _PAGE_NX)

#define PAGE_COPY_NOEXEC	__pgprot(_PAGE_PRESENT | _PAGE_USER |	\
					 _PAGE_ACCESSED | _PAGE_NX)
#define PAGE_COPY		PAGE_COPY_NOEXEC


Thanks,
Xishi Qiu