Re: [PATCH v6 RESEND] x86/boot/KASLR: Restrict kernel to be randomized in mirror regions

From: Baoquan He
Date: Fri Jul 28 2017 - 06:18:28 EST


On 07/28/17 at 11:55am, Ingo Molnar wrote:
>
> * Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx> wrote:
>
> > On Fri, 21 Jul, at 09:19:56PM, Baoquan He wrote:
> > >
> > > There are places where the efi map is getting and used like this. E.g
> > > in efi_high_alloc() of drivers/firmware/efi/libstub/efi-stub-helper.c.
> > > EFI developers worry the size of efi_memory_desc_t could not be the same
> > > as e->efi_memdesc_size?
> > >
> > > Hi Matt,
> > >
> > > Could you help have a look at this?
> >
> > You're exactly right. The code guards against the size of the
> > efi_memory_desc_t struct changing. The UEFI spec says to traverse the
> > memory map this way.
>
> This is not obvious and looks pretty ugly as well, and open coded in several
> places.
>
> At minimum we should have an efi_memdesc_ptr(efi, i) wrapper inline (or so) that
> gives us the entry pointer, plus a comment that points out that ->memdesc_size
> might not be equal to sizeof(efi_memory_memdesc_t).

Seems for_each_efi_memory_desc_in_map() can be used to hide the
calculation and type cast each time for better memmap loop.