On 11/05/2015 01:46 AM, Russell King - ARM Linux wrote:
On Wed, Nov 04, 2015 at 05:00:39PM -0800, Laura Abbott wrote:
Currently, read only permissions are not being applied even
when CONFIG_DEBUG_RODATA is set. This is because section_update
uses current->mm for adjusting the page tables. current->mm
need not be equivalent to the kernel version. Use pgd_offset_k
to get the proper page directory for updating.
What are you trying to achieve here? You can't use these functions
at run time (after the first thread has been spawned) to change
permissions, because there will be multiple copies of the kernel
section mappings, and those copies will not get updated.
In any case, this change will probably break kexec and ftrace, as
the running thread will no longer see the updated page tables.
I think I was hitting that exact problem with multiple copies
not getting updated. The section_update code was being called
and I was seeing the tables get updated but nothing was being
applied when I tried to write to text or check the debugfs
page table. The current flow is:
rest_init -> kernel_thread(kernel_init) and from that thread
mark_rodata_ro. So mark_rodata_ro is always going to happen
in a thread.
Do we need to update for both init_mm and the first running
thread?
Thanks,
Laura
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