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

[Baoquan He]

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.