From mboxrd@z Thu Jan 1 00:00:00 1970 From: Heiko Carstens Subject: Re: [PATCH 1/2] security: Change name of CONFIG_DEBUG_RODATA Date: Thu, 19 Jan 2017 12:33:05 +0100 Message-ID: <20170119113305.GB5110@osiris> References: <1484789346-21012-1-git-send-email-labbott@redhat.com> <1484789346-21012-2-git-send-email-labbott@redhat.com> <20170119105646.GA11176@leverpostej> Reply-To: kernel-hardening@lists.openwall.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: List-Post: List-Help: List-Unsubscribe: List-Subscribe: Content-Disposition: inline In-Reply-To: <20170119105646.GA11176@leverpostej> To: Mark Rutland Cc: Laura Abbott , Kees Cook , Jason Wessel , Jonathan Corbet , Russell King , Catalin Marinas , Will Deacon , "James E.J. Bottomley" , Helge Deller , Martin Schwidefsky , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, Rob Herring , "Rafael J. Wysocki" , Len Brown , Pavel Machek , Jessica Yu , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-parisc@vger.k List-Id: linux-pm@vger.kernel.org On Thu, Jan 19, 2017 at 10:56:46AM +0000, Mark Rutland wrote: > > +config HARDENED_PAGE_MAPPINGS > > + bool "Mark kernel mappings with stricter permissions (RO/W^X)" > > + default y > > + depends on ARCH_HAS_HARDENED_MAPPINGS > > + help > > + If this is set, kernel text and rodata memory will be made read-only, > > + and non-text memory will be made non-executable. This provides > > + protection against certain security attacks (e.g. executing the heap > > + or modifying text). > > + > > + Unless your system has known restrictions or performance issues, it > > + is recommended to say Y here. > > It's somewhat unfortunate that this means the feature is no longer > mandatory on arm64 (and s390+x86). We have a boot-time switch to turn > the protections off, so I was hoping we could make this mandatory on all > architectures with support. > > It would be good to see if we could make this mandatory for arm and > parisc, or if it really needs to be optional for either of those. Looks like the config option is a no-op on parisc just like it is on s390. Irrelavant of the config option at least on s390 the page tables for kernel text and rodata will be read-only anyway. This works since ages and I don't see a reason why this should be changed. Also trying to disable this with the "rodata=" command line option does not work at least on s390, and I guess this is true for parisc as well. The only thing implemented with CONFIG_DEBUG_RODATA on both architectures is to emit a message that states memory has been protected (mark_rodata_ro). This just avoids a wrong "Kernel memory protection disabled." message. So yes, I'd really like to keep this option mandatory.