* [PATCH 4.9 65/97] x86/efistub: Disable paging at mixed mode entry
[not found] <20200122092755.678349497@linuxfoundation.org>
@ 2020-01-22 9:29 ` Greg Kroah-Hartman
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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
@@ -227,6 +227,11 @@ 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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