linux-kernel - [PATCH 4.14 090/118] x86/pti: Unbreak EFI old

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Message-Id: <20180115123420.778955978@linuxfoundation.org>
Date:   Mon, 15 Jan 2018 13:35:17 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Dimitri Sivanich <sivanich@....com>,
        Jiri Kosina <jkosina@...e.cz>, Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-efi@...r.kernel.org
Subject: [PATCH 4.14 090/118] x86/pti: Unbreak EFI old_memmap

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

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

commit de53c3786a3ce162a1c815d0c04c766c23ec9c0a upstream.

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@....com>
Signed-off-by: Jiri Kosina <jkosina@...e.cz>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Matt Fleming <matt@...eblueprint.co.uk>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: linux-efi@...r.kernel.org
Link: http://lkml.kernel.org/r/nycvar.YFH.7.76.1801052215460.11852@cbobk.fhfr.pm
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/platform/efi/efi_64.c |    2 ++
 1 file changed, 2 insertions(+)

--- 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();