Date: Wed, 25 Jan 2017 12:37:14 +0100 From: Laura Abbott <labbott@...hat.com> To: Heiko Carstens <heiko.carstens@...ibm.com>, Mark Rutland <mark.rutland@....com> Cc: Kees Cook <keescook@...omium.org>, Jason Wessel <jason.wessel@...driver.com>, Jonathan Corbet <corbet@....net>, Russell King <linux@...linux.org.uk>, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>, "James E.J. Bottomley" <jejb@...isc-linux.org>, Helge Deller <deller@....de>, Martin Schwidefsky <schwidefsky@...ibm.com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org, Rob Herring <robh@...nel.org>, "Rafael J. Wysocki" <rjw@...ysocki.net>, Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>, Jessica Yu <jeyu@...hat.com>, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, linux-parisc@...r.kernel.org, linux-s390@...r.kernel.org, linux-pm@...r.kernel.org, kernel-hardening@...ts.openwall.com Subject: Re: [PATCH 1/2] security: Change name of CONFIG_DEBUG_RODATA On 01/19/2017 12:33 PM, Heiko Carstens wrote: > 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. > (Apologies, my SMTP server was set up incorrectly so this didn't get sent out when I thought it did) Okay, that's useful to know. I think I'm going to add a 'select HARDENED_MAPPINGS' (or whatever it gets changed to) to arches that were previously def_bool. This is a slight Kconfig semantic change but as has been pointed out we now have the command line option. Thanks, Laura
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