Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751628AbdLETgC (ORCPT ); Tue, 5 Dec 2017 14:36:02 -0500 Received: from mail-vk0-f66.google.com ([209.85.213.66]:41396 "EHLO mail-vk0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751156AbdLETgB (ORCPT ); Tue, 5 Dec 2017 14:36:01 -0500 X-Google-Smtp-Source: AGs4zMbeJt2LR5b9+uuU9sqM67O8ZH8bFR8cJOwolAGBdm7gVNM6T1t82vdLM1TyVi/k1GItsx04cBZ8DHF6/EmLqnA= MIME-Version: 1.0 In-Reply-To: <20171205133601.GX10595@n2100.armlinux.org.uk> References: <20170823135836.52fb44fc@gandalf.local.home> <20170823150351.606ba09f@gandalf.local.home> <20171205114709.f6aj6i426keq2cn5@camel2.lan> <20171205131416.GW10595@n2100.armlinux.org.uk> <20171205132339.behn34z6b7ci2m4j@camel2.lan> <5b9b86cf-4b62-c984-fe52-a22df8fce33c@raspberrypi.org> <20171205133601.GX10595@n2100.armlinux.org.uk> From: Kees Cook Date: Tue, 5 Dec 2017 11:35:59 -0800 X-Google-Sender-Auth: ktDzbhTKfepEYzO4f9dU2Wr_l8I Message-ID: Subject: Re: [PATCH] Arm: mm: ftrace: Only set text back to ro after kernel has been marked ro To: Russell King - ARM Linux Cc: Phil Elwell , Matthias Reichl , Steven Rostedt , LKML , Eric Anholt , Stefan Wahren , linux-rpi-kernel@lists.infradead.org, "linux-arm-kernel@lists.infradead.org" Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1359 Lines: 39 On Tue, Dec 5, 2017 at 5:36 AM, Russell King - ARM Linux wrote: > On Tue, Dec 05, 2017 at 01:30:11PM +0000, Phil Elwell wrote: >> This was my initial explanation: >> >> 1. Data which is marked __ro_after_init is initially writeable. >> >> 2. The ro_perms data covers kernel text, read-only data and __ro_after_init data. >> >> 3. set_kernel_text_rw marks everything in ro_perms as writeable. >> >> 4. set_kernel_text_ro marks everything in ro_perms as read-only, including the __ro_after_init data. >> >> 5. Using the function tracing code involves code modification, resulting in calls to >> __ftrace_modify_code and set_kernel_text_ro. >> >> 6. Therefore if function tracing is enabled before kernel_init has completed then the __ro_after_init >> data is made read-only prematurely. > > My question still stands, but let me rephrase. Do we need > set_kernel_text_*() to touch the read-only data? We don't _need_ to, but they're all contiguous, so the ro_perms array used by set_kernel_text_*() is actually only a single entry: static struct section_perm ro_perms[] = { /* Make kernel code and rodata RX (set RO). */ { .name = "text/rodata RO", .start = (unsigned long)_stext, .end = (unsigned long)__init_begin, ... -Kees -- Kees Cook Pixel Security