Re: [PATCH 2/2] ARM: mm: keep rodata non-executable

From: Kees Cook
Date: Tue Apr 01 2014 - 19:00:14 EST

On Tue, Apr 1, 2014 at 3:54 PM, Laura Abbott <lauraa@xxxxxxxxxxxxxx> wrote:
> On 4/1/2014 3:34 PM, Kees Cook wrote:
>> On Mon, Mar 24, 2014 at 3:47 AM, Jon Medhurst (Tixy) <tixy@xxxxxxxxxx> wrote:
>>> On Sun, 2014-03-23 at 16:21 -0600, Kees Cook wrote:
>>>> For this stage, how about I make this "depends on KEXEC=n &&
>>>> KPROBES=n"?
>>> There's also ftrace (CONFIG_DYNAMIC_FTRACE I believe) which modifies
>>> kernel code with a call to probe_kernel_write(), which GDB uses as well.
>>> And grepping for the patch_text() function also shows
>>> __arch_jump_label_transform() modifies kernel code. Not sure how and
>>> when that gets used.
>> Right, so, I'm trying to fix ftrace now, and I've hit a wall. It is as
>> if changes to the kernel text PMD aren't being noticed after the
>> kernel is running. Does anyone know why this might be happening?
>> Code and details here:
>> -Kees
> We had a flush_tlb_kernel_page after the pmd_flush in our out of tree code
> which makes the text writeable in __patch_text.

I tried flush_tlb_kernel_range(), which I'd expect to do the same
thing. I can try with _page() too.


Kees Cook
Chrome OS Security
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