arm64/efi: set PE/COFF file alignment to 512 bytes

Change our PE/COFF header to use the minimum file alignment of
512 bytes (0x200), as mandated by the PE/COFF spec v8.3

Also update the linker script so that the Image file itself is also a
round multiple of FileAlignment.
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Roy Franz <roy.franz@linaro.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

arch/arm64/kernel/head.S

@@ -162,7 +162,7 @@ optional_header:
 extra_header_fields:
 	.quad	0				// ImageBase
 	.long	0x1000				// SectionAlignment
-	.long	0x8				// FileAlignment
+	.long	PECOFF_FILE_ALIGNMENT		// FileAlignment
 	.short	0				// MajorOperatingSystemVersion
 	.short	0				// MinorOperatingSystemVersion
 	.short	0				// MajorImageVersion

arch/arm64/kernel/vmlinux.lds.S

@@ -32,6 +32,22 @@ jiffies = jiffies_64;
 	*(.hyp.text)					\
 	VMLINUX_SYMBOL(__hyp_text_end) = .;
 
+/*
+ * The size of the PE/COFF section that covers the kernel image, which
+ * runs from stext to _edata, must be a round multiple of the PE/COFF
+ * FileAlignment, which we set to its minimum value of 0x200. 'stext'
+ * itself is 4 KB aligned, so padding out _edata to a 0x200 aligned
+ * boundary should be sufficient.
+ */
+PECOFF_FILE_ALIGNMENT = 0x200;
+
+#ifdef CONFIG_EFI
+#define PECOFF_EDATA_PADDING	\
+	.pecoff_edata_padding : { BYTE(0); . = ALIGN(PECOFF_FILE_ALIGNMENT); }
+#else
+#define PECOFF_EDATA_PADDING
+#endif
+
 SECTIONS
 {
 	/*
@@ -103,6 +119,7 @@ SECTIONS
 	_data = .;
 	_sdata = .;
 	RW_DATA_SECTION(64, PAGE_SIZE, THREAD_SIZE)
+	PECOFF_EDATA_PADDING
 	_edata = .;
 
 	BSS_SECTION(0, 0, 0)