efi/x86: Add kernel preferred address to PE header

Store the kernel's link address as ImageBase in the PE header. Note that
the PE specification requires the ImageBase to be 64k aligned. The
preferred address should almost always satisfy that, except for 32-bit
kernel if the configuration has been customized.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200303221205.4048668-4-nivedita@alum.mit.edu
Link: https://lore.kernel.org/r/20200308080859.21568-18-ardb@kernel.org

arch/x86/boot/header.S

@@ -138,10 +138,12 @@ optional_header:
 #endif
 
 extra_header_fields:
+	# PE specification requires ImageBase to be 64k aligned
+	.set	image_base, (LOAD_PHYSICAL_ADDR + 0xffff) & ~0xffff
 #ifdef CONFIG_X86_32
-	.long	0				# ImageBase
+	.long	image_base			# ImageBase
 #else
-	.quad	0				# ImageBase
+	.quad	image_base			# ImageBase
 #endif
 	.long	0x20				# SectionAlignment
 	.long	0x20				# FileAlignment