Re: [PATCH 5/6] x86/efi: Build our own page table structures

Matt Fleming
2015-11-12T21:39:09Z

On Thu, 12 Nov, at 07:38:13PM, Borislav Petkov wrote:
> > @@ -831,6 +831,12 @@ static void __init __efi_enter_virtual_mode(void)
> > efi.systab = NULL;
> >
> > efi_merge_regions();
> > + if (efi_alloc_page_tables()) {
> > + pr_err("Failed to allocate EFI page tables\n");
> > + clear_bit(EFI_RUNTIME_SERVICES, &efi.flags);
> > + return;
> > + }
>
> This should happen before efi_merge_regions() - no need to merge if we
> can't alloc PGT.

Fair point.

> > +
> > new_memmap = efi_map_regions(&count, &pg_shift);
> > if (!new_memmap) {
> > pr_err("Error reallocating memory, EFI runtime non-functional!\n");
> > @@ -888,29 +894,12 @@ static void __init __efi_enter_virtual_mode(void)
> >
> > efi_runtime_mkexec();
> >
> > - /*
> > - * We mapped the descriptor array into the EFI pagetable above but we're
> > - * not unmapping it here. Here's why:
> > - *
> > - * We're copying select PGDs from the kernel page table to the EFI page
> > - * table and when we do so and make changes to those PGDs like unmapping
> > - * stuff from them, those changes appear in the kernel page table and we
> > - * go boom.
> > - *
> > - * From setup_real_mode():
> > - *
> > - * ...
> > - * trampoline_pgd[0] = init_level4_pgt[pgd_index(__PAGE_OFFSET)].pgd;
> > - *
> > - * In this particular case, our allocation is in PGD 0 of the EFI page
> > - * table but we've copied that PGD from PGD[272] of the EFI page table:
> > - *
> > - * pgd_index(__PAGE_OFFSET = 0xffff880000000000) = 272
> > - *
> > - * where the direct memory mapping in kernel space is.
> > - *
> > - * new_memmap's VA comes from that direct mapping and thus clearing it,
> > - * it would get cleared in the kernel page table too.
> > + /*
>
> ERROR: code indent should use tabs where possible
> #149: FILE: arch/x86/platform/efi/efi.c:897:
> + /*$
>
> ...

Dammit vim. I'll fix this.

> > void efi_sync_low_kernel_mappings(void)
> > {
> > - unsigned num_pgds;
> > - pgd_t *pgd = (pgd_t *)__va(real_mode_header->trampoline_pgd);
> > + unsigned num_entries;
> > + pgd_t *pgd_k, *pgd_efi;
> > + pud_t *pud_k, *pud_efi;
> >
> > if (efi_enabled(EFI_OLD_MEMMAP))
> > return;
> >
> > - num_pgds = pgd_index(MODULES_END - 1) - pgd_index(PAGE_OFFSET);
> > + /*
> > + * We can share all PGD entries apart from the one entry that
> > + * covers the EFI runtime mapping space.
> > + *
> > + * Make sure the EFI runtime region mappings are guaranteed to
> > + * only span a single PGD entry and that the entry also maps
> > + * other important kernel regions.
> > + */
> > + BUILD_BUG_ON(pgd_index(EFI_VA_END) != pgd_index(MODULES_END));
> > + BUILD_BUG_ON((EFI_VA_START & PGDIR_MASK) !=
> > + (EFI_VA_END & PGDIR_MASK));
>
> You can align them in a more readable way:
>
> BUILD_BUG_ON((EFI_VA_START & PGDIR_MASK) !=
> (EFI_VA_END & PGDIR_MASK));

Sure.