efi/x86: Respect 32-bit ABI in efi32_pe_entry()

verify_cpu() clobbers BX and DI. In case we have to return error, we need
to preserve them to respect the 32-bit calling convention.

Signed-off-by: Arvind Sankar <[email protected]>
Signed-off-by: Ard Biesheuvel <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Link: https://lore.kernel.org/r/[email protected]

Author: nivedita76

arch/x86/boot/compressed/head_64.S

@@ -660,7 +660,11 @@ SYM_DATA(efi_is64, .byte 1)
 SYM_FUNC_START(efi32_pe_entry)
 	pushl	%ebp
 
+	pushl	%ebx
+	pushl	%edi
 	call	verify_cpu			// check for long mode support
+	popl	%edi
+	popl	%ebx
 	testl	%eax, %eax
 	movl	$0x80000003, %eax		// EFI_UNSUPPORTED
 	jnz	3f