Messages in this thread |  | | Date | Fri, 14 Feb 2014 11:11:07 -0800 | Subject | Re: [PATCH 2/2] ARM: mm: keep rodata non-executable | From | Kees Cook <> |
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On Fri, Feb 14, 2014 at 8:22 AM, Dave Martin <Dave.Martin@arm.com> wrote: > On Thu, Feb 13, 2014 at 05:04:10PM -0800, Kees Cook wrote: >> Introduce "CONFIG_DEBUG_RODATA" to mostly match the x86 config, though >> the behavior is different: it depends on STRICT_KERNMEM_PERMS, which >> sets rodata read-only (but executable), where as this option additionally >> splits rodata from the kernel text (resulting in potentially more memory >> lost to padding) and sets it non-executable as well. The end result is >> that on builds with CONFIG_DEBUG_RODATA=y (like x86) the rodata with be >> marked purely read-only. > > This triggers an Oops in kexec, because we have a block of code in .text > which is a template for generating baremetal code to relocate the new > kernel, and some literal words are written into it before copying.
You're writing into the text area? I would imagine that CONFIG_ARM_KERNMEM_PERMS would break that. However, that's not the right place to be building code -- shouldn't the module area be used for that?
> Possibly this should be in .rodata, not .text.
Well, rodata should be neither writable nor executable.
> There may be a few other instances of this kind of thing.
This config will certainly find them! :) But, that's why it's behind a config.
> Are you aware of similar situations on other arches?
I think there were some problems a long time ago on x86 for rodata too.
-Kees
-- Kees Cook Chrome OS Security
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