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