On Wed, 6 Aug 2014, Kees Cook wrote:

With the original code, there is (I think) a page table entry for the
fixmap range. For the latter, there isn't. I see a NULL pgd entry
fault when trying to use it, and noticed that this only exists under
highmem:

static void __init kmap_init(void)
{
#ifdef CONFIG_HIGHMEM
        pkmap_page_table = early_pte_alloc(pmd_off_k(PKMAP_BASE),
                PKMAP_BASE, _PAGE_KERNEL_TABLE);

        fixmap_page_table = early_pte_alloc(pmd_off_k(FIXADDR_START),
                FIXADDR_START, _PAGE_KERNEL_TABLE);
#endif
}

The above is wrong.  The fixmap PTEs must be allocated unconditionally 
irrespective of highmem.  So the #endif should be moved up by 3 lines.


Nicolas