The following commit has been merged into the efi/urgent branch of tip:

Commit-ID: 4911ee401b7ceff8f38e0ac597cbf503d71e690c Gitweb: https://git.kernel.org/tip/4911ee401b7ceff8f38e0ac597cbf503d71e690c Author: Ard Biesheuvel ardb@kernel.org AuthorDate: Tue, 24 Dec 2019 14:29:09 +01:00 Committer: Ingo Molnar mingo@kernel.org 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 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 --- 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 SYM_FUNC_END(efi32_stub_entry) #endif