Il 10/10/2010 18:46, Andi Kleen ha scritto:
> This won't work at all on x86 because you don't handle large
> pages.
>
> And it doesn't work on x86-64 because the first 2GB are double
> mapped (direct and kernel text mapping)
>
> Thirdly I expect it won't either on architectures that map
> the direct mapping with special registers (like IA64 or MIPS)
Andi, what do you think to use the already implemented follow_pte
instead?
int writeable_kernel_pte_range(unsigned long address, unsigned long size,
unsigned int rw)
{
unsigned long addr = address & PAGE_MASK;
unsigned long end = address + size;
unsigned long start = addr;
int ret = -EINVAL;
pte_t *ptep, pte;
spinlock_t *lock = &init_mm.page_table_lock;
do {
ret = follow_pte(&init_mm, addr, &ptep, &lock);
if (ret)
goto out;
pte = *ptep;
if (pte_present(pte)) {
pte = rw ? pte_mkwrite(pte) : pte_wrprotect(pte);
*ptep = pte;
}
pte_unmap_unlock(ptep, lock);
addr += PAGE_SIZE;
} while (addr && (addr < end));
ret = 0;
out:
flush_tlb_kernel_range(start, end);
return ret;
}
>
> I'm not sure this is very useful anyways. It doesn't protect
> against stray DMA and it doesn't protect against writes through
> broken user PTEs.
>
> -Andi
>
It's a way to have more protection against kernel bug, for a
in-memory fs can be important. However this option can be
enabled/disabled at fs level.
Marco
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