On Fri, Feb 14, 2014 at 11:11:07AM -0800, Kees Cook wrote: > On Fri, Feb 14, 2014 at 8:22 AM, Dave Martin <dave.mar...@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.
We're not writing into code exactly. This code is never executed in-place in vmlinux. It gets copied, and only copies are ever executed. Some pointers and offsets get poked into the code to configure it. I think it would be better simply to put the code in .rodata, and poke paramaters into the copy, not the original -- but that's a bit more awkward to code up, since the values can't be poked simply by writing global variables. > > > 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. I haven't tested exhaustively, but it think this is sufficient for a Tested-by. The patch does seem to be doing what it is intended to do, and doesn't seem to be triggering false positives all over the place. > > > Are you aware of similar situations on other arches? > > I think there were some problems a long time ago on x86 for rodata too. It would be good to get this kexec case fixed -- I'll try to hack up a separate patch. Cheers ---Dave -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
