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* [PATCH 4.4 51/76] x86/efistub: Disable paging at mixed mode entry
       [not found] <20200122092751.587775548@linuxfoundation.org>
@ 2020-01-22  9:29 ` Greg Kroah-Hartman
  0 siblings, 0 replies; only message in thread
From: Greg Kroah-Hartman @ 2020-01-22  9:29 UTC (permalink / raw)
  To: linux-kernel
  Cc: Greg Kroah-Hartman, stable, Ard Biesheuvel, Arvind Sankar,
	Hans de Goede, Linus Torvalds, Peter Zijlstra, Thomas Gleixner,
	linux-efi, Ingo Molnar

From: Ard Biesheuvel <ardb@kernel.org>

commit 4911ee401b7ceff8f38e0ac597cbf503d71e690c upstream.

The EFI mixed mode entry code goes through the ordinary startup_32()
routine before jumping into the kernel's EFI boot code in 64-bit
mode. The 32-bit startup code must be entered with paging disabled,
but this is not documented as a requirement for the EFI handover
protocol, and so we should disable paging explicitly when entering
the kernel from 32-bit EFI firmware.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Cc: <stable@vger.kernel.org>
Cc: Arvind Sankar <nivedita@alum.mit.edu>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Link: https://lkml.kernel.org/r/20191224132909.102540-4-ardb@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/x86/boot/compressed/head_64.S |    5 +++++
 1 file changed, 5 insertions(+)

--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -225,6 +225,11 @@ ENTRY(efi32_stub_entry)
 	leal	efi32_config(%ebp), %eax
 	movl	%eax, efi_config(%ebp)
 
+	/* Disable paging */
+	movl	%cr0, %eax
+	btrl	$X86_CR0_PG_BIT, %eax
+	movl	%eax, %cr0
+
 	jmp	startup_32
 ENDPROC(efi32_stub_entry)
 #endif



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2020-01-22  9:29 ` [PATCH 4.4 51/76] x86/efistub: Disable paging at mixed mode entry Greg Kroah-Hartman

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