Kees Cook keescook at chromium.org
Thu Apr 3 16:14:54 PDT 2014

On Tue, Apr 1, 2014 at 4:08 PM, Rabin Vincent <rabin at rab.in> wrote:
> 2014-04-01 20:36 GMT+02:00 Kees Cook <keescook at chromium.org>:
>> Is there something "sticky" about PMD sections that I'm not aware of?
>> Even after calling set_kernel_text_rw(), any writes to kernel memory
>> fault. :(
> section_update() updates init_mm, but each mm has a copy of the first
> level page tables.  So your updates to init_mm won't be visibile to
> currently running processes.  (Have a look at arch/arm/mm/ioremap.c's
> vmalloc_seq stuff for some background on how section support is
> handled on non-SMP; the vmalloc code doesn't use sections on SMP.)

Ah-ha! This is the missing piece of information for me. :)

> Here's a patch (probably whitespace damaged, hence also attached) with
> which dynamic ftrace works for me on top your other paches.  Tested on
> a non-LPAE SMP.

Thanks! I'll incorporate calls to set_all_modules_text_rw/ro and see
what I can make work.


Kees Cook
Chrome OS Security

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