From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755482AbcA1OgR (ORCPT ); Thu, 28 Jan 2016 09:36:17 -0500 Received: from mail-wm0-f43.google.com ([74.125.82.43]:38033 "EHLO mail-wm0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753234AbcA1OgO convert rfc822-to-8bit (ORCPT ); Thu, 28 Jan 2016 09:36:14 -0500 MIME-Version: 1.0 In-Reply-To: <1453960307-10181-5-git-send-email-computersforpeace@gmail.com> References: <1453960307-10181-1-git-send-email-computersforpeace@gmail.com> <1453960307-10181-5-git-send-email-computersforpeace@gmail.com> Date: Thu, 28 Jan 2016 11:36:13 -0300 Message-ID: Subject: Re: [PATCH 4/8] mtd: spi-nor: disallow further writes to SR if WP# is low From: Ezequiel Garcia To: Brian Norris Cc: "linux-mtd@lists.infradead.org" , =?UTF-8?B?UmFmYcWCIE1pxYJlY2tp?= , Boris Brezillon , "linux-kernel@vger.kernel.org" , Bayi Cheng , Marek Vasut , Daniel Kurtz Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 28 January 2016 at 02:51, Brian Norris wrote: > Locking the flash is most useful if it provides real hardware security. > Otherwise, it's little more than a software permission bit. > > A reasonable use case that provides real HW security might be like > follows: > > (1) hardware WP# is deasserted > (2) program flash > (3) flash range is protected via status register > (4) hardware WP# is asserted > (5) flash protection range can no longer be changed, until WP# is > deasserted > > In this way, flash protection is co-owned by hardware and software. > > Now, one would expect to be able to perform step (3) with > ioctl(MEMLOCK), except that the spi-nor driver does not set the Status > Register Protect bit (a.k.a. Status Register Write Disable (SRWD)), so > even though the range is now locked, it does not satisfy step (5) -- it > can still be changed by a call to ioctl(MEMUNLOCK). > > So, let's enable status register protection after the first lock > command. > > Signed-off-by: Brian Norris > --- > drivers/mtd/spi-nor/spi-nor.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c > index 3a08aa53c171..46da6bb706fa 100644 > --- a/drivers/mtd/spi-nor/spi-nor.c > +++ b/drivers/mtd/spi-nor/spi-nor.c > @@ -518,6 +518,9 @@ static int stm_lock(struct spi_nor *nor, loff_t ofs, uint64_t len) > > status_new = (status_old & ~mask) | val; > > + /* Disallow further writes if WP pin is asserted */ > + status_new |= SR_SRWD; > + No need to clear SR_SRWD in stm_unlock? -- Ezequiel García, VanguardiaSur www.vanguardiasur.com.ar