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Subject[tip: efi/urgent] x86/efistub: Disable paging at mixed mode entry
The following commit has been merged into the efi/urgent branch of tip:

Commit-ID: 4911ee401b7ceff8f38e0ac597cbf503d71e690c
Author: Ard Biesheuvel <>
AuthorDate: Tue, 24 Dec 2019 14:29:09 +01:00
Committer: Ingo Molnar <>
CommitterDate: Wed, 25 Dec 2019 10:46:07 +01:00

x86/efistub: Disable paging at mixed mode entry

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 <>
Cc: <>
Cc: Arvind Sankar <>
Cc: Hans de Goede <>
Cc: Linus Torvalds <>
Cc: Peter Zijlstra <>
Cc: Thomas Gleixner <>
Signed-off-by: Ingo Molnar <>
arch/x86/boot/compressed/head_64.S | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 58a512e..ee60b81 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -244,6 +244,11 @@ SYM_FUNC_START(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
 \ /
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