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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