On Tue, Feb 18, 2014 at 10:10:03AM -0800, Kees Cook wrote: > On Mon, Feb 17, 2014 at 4:34 AM, Dave Martin <dave.mar...@arm.com> wrote: > > 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. > > Okay, interesting. I'll be curious to see what the patch for this looks like. > > >> > 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. > > Great, thanks for taking the time to check on it! > > Should I send this to the patch tracker, or wait for more feedback?
It would be good if someone who's more familiar with the parms and vmlinux.lds stuff could take a look at it, though I don't see any obvious problem yet. If you don't receive further comments, you could try reposting once to alert people to the fact that you're still waiting. 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/
