[tip:x86/pti] x86/pti: Unbreak EFI old_memmap

[tip-bot for Jiri Kosina]

Commit-ID:  5ad9a697fa957e61d50ef969179c18348968cd9f
Gitweb:     https://git.kernel.org/tip/5ad9a697fa957e61d50ef969179c18348968cd9f
Author:     Jiri Kosina <jkosina@xxxxxxx>
AuthorDate: Fri, 5 Jan 2018 22:35:41 +0100
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Sat, 6 Jan 2018 11:43:44 +0100

x86/pti: Unbreak EFI old_memmap

EFI_OLD_MEMMAP's efi_call_phys_prolog() calls set_pgd() with swapper PGD that
has PAGE_USER set, which makes PTI set NX on it, and therefore EFI can't
execute it's code.

Fix that by forcefully clearing _PAGE_NX from the PGD (this can't be done
by the pgprot API).

_PAGE_NX will be automatically reintroduced in efi_call_phys_epilog(), as
_set_pgd() will again notice that this is _PAGE_USER, and set _PAGE_NX on
it.

Tested-by: Dimitri Sivanich <sivanich@xxxxxxx>
Signed-off-by: Jiri Kosina <jkosina@xxxxxxx>
Acked-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: linux-efi@xxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/nycvar.YFH.7.76.1801052215460.11852@xxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/platform/efi/efi_64.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
index 39c4b35..61975b6 100644
--- a/arch/x86/platform/efi/efi_64.c
+++ b/arch/x86/platform/efi/efi_64.c
@@ -134,7 +134,9 @@ pgd_t * __init efi_call_phys_prolog(void)
 				pud[j] = *pud_offset(p4d_k, vaddr);
 			}
 		}
+		pgd_offset_k(pgd * PGDIR_SIZE)->pgd &= ~_PAGE_NX;
 	}
+
 out:
 	__flush_tlb_all();