From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yk0-f175.google.com (mail-yk0-f175.google.com [209.85.160.175]) by kanga.kvack.org (Postfix) with ESMTP id 2127A82F64 for ; Thu, 5 Nov 2015 11:20:46 -0500 (EST) Received: by ykba4 with SMTP id a4so139350771ykb.3 for ; Thu, 05 Nov 2015 08:20:46 -0800 (PST) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id 76si1570463vkd.7.2015.11.05.08.20.45 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 05 Nov 2015 08:20:45 -0800 (PST) Subject: Re: [PATCH] arm: Use kernel mm when updating section permissions References: <1446685239-28522-1-git-send-email-labbott@fedoraproject.org> <20151105094615.GP8644@n2100.arm.linux.org.uk> From: Laura Abbott Message-ID: <563B81DA.2080409@redhat.com> Date: Thu, 5 Nov 2015 08:20:42 -0800 MIME-Version: 1.0 In-Reply-To: <20151105094615.GP8644@n2100.arm.linux.org.uk> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Russell King - ARM Linux , Laura Abbott Cc: Kees Cook , Catalin Marinas , Will Deacon , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org On 11/05/2015 01:46 AM, Russell King - ARM Linux wrote: > On Wed, Nov 04, 2015 at 05:00:39PM -0800, Laura Abbott wrote: >> Currently, read only permissions are not being applied even >> when CONFIG_DEBUG_RODATA is set. This is because section_update >> uses current->mm for adjusting the page tables. current->mm >> need not be equivalent to the kernel version. Use pgd_offset_k >> to get the proper page directory for updating. > > What are you trying to achieve here? You can't use these functions > at run time (after the first thread has been spawned) to change > permissions, because there will be multiple copies of the kernel > section mappings, and those copies will not get updated. > > In any case, this change will probably break kexec and ftrace, as > the running thread will no longer see the updated page tables. > I think I was hitting that exact problem with multiple copies not getting updated. The section_update code was being called and I was seeing the tables get updated but nothing was being applied when I tried to write to text or check the debugfs page table. The current flow is: rest_init -> kernel_thread(kernel_init) and from that thread mark_rodata_ro. So mark_rodata_ro is always going to happen in a thread. Do we need to update for both init_mm and the first running thread? Thanks, Laura -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org