Re: [RFC v1 3/4] x86, boot: Implement ASLR for kernel memory sections (x86_64)

Joerg Roedel
2016-04-19T14:28:09Z

Hi Thomas,

On Fri, Apr 15, 2016 at 03:03:12PM -0700, Thomas Garnier wrote:
> +/*
> + * Create PGD aligned trampoline table to allow real mode initialization
> + * of additional CPUs. Consume only 1 additonal low memory page.
> + */
> +void __meminit kaslr_trampoline_init(unsigned long page_size_mask)
> +{
> + unsigned long addr, next, end;
> + pgd_t *pgd;
> + pud_t *pud_page, *tr_pud_page;
> + int i;
> +
> + if (!kaslr_enabled()) {
> + trampoline_pgd_entry = init_level4_pgt[pgd_index(PAGE_OFFSET)];
> + return;
> + }
> +
> + tr_pud_page = alloc_low_page();
> + set_pgd(&trampoline_pgd_entry, __pgd(_PAGE_TABLE | __pa(tr_pud_page)));
> +
> + addr = 0;
> + end = ISA_END_ADDRESS;
> + pgd = pgd_offset_k((unsigned long)__va(addr));
> + pud_page = (pud_t *) pgd_page_vaddr(*pgd);
> +
> + for (i = pud_index(addr); i < PTRS_PER_PUD; i++, addr = next) {
> + pud_t *pud, *tr_pud;
> + pmd_t *pmd;
> +
> + tr_pud = tr_pud_page + pud_index(addr);
> + pud = pud_page + pud_index((unsigned long)__va(addr));
> + next = (addr & PUD_MASK) + PUD_SIZE;
> +
> + if (addr >= end || !pud_val(*pud)) {
> + if (!after_bootmem &&
> + !e820_any_mapped(addr & PUD_MASK, next, E820_RAM) &&
> + !e820_any_mapped(addr & PUD_MASK, next,
> + E820_RESERVED_KERN))
> + set_pud(tr_pud, __pud(0));
> + continue;
> + }
> +
> + if (page_size_mask & (1<<PG_LEVEL_1G)) {
> + set_pte((pte_t *)tr_pud,
> + pfn_pte((__pa(addr) & PUD_MASK) >> PAGE_SHIFT,

Hmm, why do you treat addr as virtual here, before it was a physical
address, no?

> + PAGE_KERNEL_LARGE));
> + continue;
> + }

Why do you need to check these two cases above, can't you just copy the
pud-entries like done below? The direct mapping should already take care
of unmapped regions and 1gb pages.

> + pmd = pmd_offset(pud, 0);
> + set_pud(tr_pud, __pud(_PAGE_TABLE | __pa(pmd)));
> + }
> +}

Joerg