From: Ard Biesheuvel <ardb@xxxxxxxxxx> 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@xxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Cc: Arvind Sankar <nivedita@xxxxxxxxxxxx> Cc: Hans de Goede <hdegoede@xxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: linux-efi@xxxxxxxxxxxxxxx Link: https://lkml.kernel.org/r/20191224132909.102540-4-ardb@xxxxxxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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 @@ -244,6 +244,11 @@ 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
