Re: [PATCH] x86/boot/KASLR: exclude EFI_BOOT_SERVICES_{CODE|DATA} from KASLR's choice

Baoquan He
2017-07-07T03:08:04Z

On 07/06/17 at 03:57pm, Matt Fleming wrote:
> On Thu, 06 Jul, at 08:31:07AM, Naoya Horiguchi wrote:
> > + for (i = 0; i < nr_desc; i++) {
> > + md = (efi_memory_desc_t *)(pmap + (i * e->efi_memdesc_size));
> > +
> > + /*
> > + * EFI_BOOT_SERVICES_{CODE|DATA} are avoided because boot
> > + * services regions could be accessed after ExitBootServices()
> > + * due to the workaround for buggy firmware.
> > + */
> > + if (!(md->type == EFI_LOADER_CODE ||
> > + md->type == EFI_LOADER_DATA ||
> > + md->type == EFI_CONVENTIONAL_MEMORY))
> > + continue;
>
> Wouldn't it make more sense to *only* use EFI_CONVENTIONAL_MEMORY?
>
> You can't re-use EFI_LOADER_* regions because the kaslr code is run so
> early in boot that you've no idea if data the kernel will need is in
> those EFI_LOADER_* regions.
>
> For example, we pass struct setup_data objects inside of
> EFI_LOADER_DATA regions.

It doesn't matter because we have tried to avoid those memory setup_data
resides in in mem_avoid_overlap(). Here discarding EFI_LOADER_* could
discard the whole regions while setup_data could occupy small part of
them.