linux-kernel - [PATCH] PTI: unbreak EFI old

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Date:   Fri, 5 Jan 2018 22:35:41 +0100 (CET)
From:   Jiri Kosina <jikos@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
cc:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andrea Arcangeli <aarcange@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Dimitri Sivanich <sivanich@....com>
Subject: [PATCH] PTI: unbreak EFI old_memmap

From: Jiri Kosina <jkosina@...e.cz>

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.

Signed-off-by: Jiri Kosina <jkosina@...e.cz>
Tested-by: Dimitri Sivanich <sivanich@....com>
Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>
--- 
 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 d87ac96e37ed..2dd15e967c3f 100644
--- a/arch/x86/platform/efi/efi_64.c
+++ b/arch/x86/platform/efi/efi_64.c
@@ -135,7 +135,9 @@ 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();
 

-- 
Jiri Kosina
SUSE Labs