Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page table mappings

[Andy Lutomirski]

On Wed, Feb 24, 2016 at 8:41 AM, Borislav Petkov <bp@xxxxxxxxx> wrote:
> On Wed, Feb 24, 2016 at 05:20:02PM +0100, Borislav Petkov wrote:
>> That's mixed mode. I think you mean the FLUSH_TLB_ALL in efi_call.
>> That's EFI on 64-bit but that is mandated by the spec, AFAIR.
>
> Ok, so mfleming set me straight on IRC - that's tip/master I should be
> staring at.
>
> In any case, I think we should do __flush_tlb_all() in efi_call_cirt()
> just in case, for the simple reason that EFI could be installing some
> funky TLB entries which we don't want. I'm not saying it does and it
> probably won't but what's stopping it?
>
> Or am I being overly paranoid?

I think you may be overly paranoid here.  At least no working 32-bit
EFI does this because we run it in compat mode.  Any paging entries it
inserts would be misinterpreted and likely immediately cause a crash.
Also, the EFI code doesn't know a virtual address through which to
reference the paging structures in the first place -- it could read
CR3, but that gives a physical address, and it's not at all clear to
me what even the crazier firmware authors would do with a physical
address that doesn't live in EFI-defined ranges.

--Andy