howto set some kernel pages to readonly?

[Peter Wächtler]

Am Donnerstag, 7. April 2011, 20:26:36 schrieb Peter Wächtler:
> Hello Linux ARM developers,
> 
> on Linux x86 there is infrastructure to set rodata to, aeh, readonly. ;)
> 
> I also want to protect some pages to readonly  as a guard.
> So if some kernel code writes to the memory the kernel panics.
> 
> I tried the following without success:
> 
> And I have to admit that I don't understand all the macros for
> manipulating the page table entries ;(
> Any clue what's wrong?
> 
> 
> int set_page_ro(unsigned long addr)
> {
>         pte_t new_pte;
>         unsigned long pfn;
>         pte_t *pte;
>         pgd_t *pgd;
>         pmd_t *pmd;
> 
>         pgd = pgd_offset_k(addr);
>         pmd = pmd_offset(pgd, addr);
> 
>         pfn = __phys_to_pfn(virt_to_phys((void*)addr));
> 
>         pte = pte_offset_kernel(pmd, addr);
>         new_pte = pfn_pte(pfn, __pgprot(pgprot_val(pgprot_kernel) |
>                                                       (__PAGE_READONLY)) );
> 
>         set_pte_ext(pte, new_pte, 0);
> 
>         return 0;
> }
> 
> 
> set_page_ro( (unsigned long)pa );
> flush_tlb_kernel_page((long)pa);
> 

While the variable is named "pa" - it's actually a virtual address.
The code has to run on a SMP box - ARM 1136 multi core (ARMv6).