[PATCH v5 6/7] RISC-V: Add PE/COFF header for EFI stub

[Ard Biesheuvel <ardb@kernel.org>]

From: Atish Patra <atish.patra@wdc.com>

Linux kernel Image can appear as an EFI application With appropriate
PE/COFF header fields in the beginning of the Image header. An EFI
application loader can directly load a Linux kernel Image and an EFI
stub residing in kernel can boot Linux kernel directly.

Add the necessary PE/COFF header.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Link: https://lore.kernel.org/r/20200421033336.9663-3-atish.patra@wdc.com
[ardb: - use C prefix for c.li to ensure the expected opcode is emitted
       - align all image sections according to PE/COFF section alignment ]
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/riscv/include/asm/sections.h |  13 +++
 arch/riscv/kernel/Makefile        |   4 +
 arch/riscv/kernel/efi-header.S    | 100 ++++++++++++++++++++
 arch/riscv/kernel/head.S          |  16 ++++
 arch/riscv/kernel/image-vars.h    |  53 +++++++++++
 arch/riscv/kernel/vmlinux.lds.S   |  22 ++++-
 6 files changed, 206 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/include/asm/sections.h b/arch/riscv/include/asm/sections.h
new file mode 100644
index 000000000000..3a9971b1210f
--- /dev/null
+++ b/arch/riscv/include/asm/sections.h
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2020 Western Digital Corporation or its affiliates.
+ */
+#ifndef __ASM_SECTIONS_H
+#define __ASM_SECTIONS_H
+
+#include <asm-generic/sections.h>
+
+extern char _start[];
+extern char _start_kernel[];
+
+#endif /* __ASM_SECTIONS_H */
diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index 86c83081044f..86ca755f8a9f 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -32,6 +32,10 @@ obj-y	+= patch.o
 obj-$(CONFIG_MMU) += vdso.o vdso/
 
 obj-$(CONFIG_RISCV_M_MODE)	+= clint.o traps_misaligned.o
+OBJCOPYFLAGS := --prefix-symbols=__efistub_
+$(obj)/%.stub.o: $(obj)/%.o FORCE
+	$(call if_changed,objcopy)
+
 obj-$(CONFIG_FPU)		+= fpu.o
 obj-$(CONFIG_SMP)		+= smpboot.o
 obj-$(CONFIG_SMP)		+= smp.o
diff --git a/arch/riscv/kernel/efi-header.S b/arch/riscv/kernel/efi-header.S
new file mode 100644
index 000000000000..72c997450366
--- /dev/null
+++ b/arch/riscv/kernel/efi-header.S
@@ -0,0 +1,100 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2020 Western Digital Corporation or its affiliates.
+ * Adapted from arch/arm64/kernel/efi-header.S
+ */
+
+#include <linux/pe.h>
+#include <linux/sizes.h>
+
+	.macro	__EFI_PE_HEADER
+	.long	PE_MAGIC
+coff_header:
+	.short	IMAGE_FILE_MACHINE_RISCV64		// Machine
+	.short	section_count				// NumberOfSections
+	.long	0 					// TimeDateStamp
+	.long	0					// PointerToSymbolTable
+	.long	0					// NumberOfSymbols
+	.short	section_table - optional_header		// SizeOfOptionalHeader
+	.short	IMAGE_FILE_DEBUG_STRIPPED | \
+		IMAGE_FILE_EXECUTABLE_IMAGE | \
+		IMAGE_FILE_LINE_NUMS_STRIPPED		// Characteristics
+
+optional_header:
+	.short	PE_OPT_MAGIC_PE32PLUS			// PE32+ format
+	.byte	0x02					// MajorLinkerVersion
+	.byte	0x14					// MinorLinkerVersion
+	.long	__pecoff_text_end - efi_header_end	// SizeOfCode
+	.long	__pecoff_data_virt_size			// SizeOfInitializedData
+	.long	0					// SizeOfUninitializedData
+	.long	__efistub_efi_entry - _start		// AddressOfEntryPoint
+	.long	efi_header_end - _start			// BaseOfCode
+
+extra_header_fields:
+	.quad	0					// ImageBase
+	.long	PECOFF_SECTION_ALIGNMENT		// SectionAlignment
+	.long	PECOFF_FILE_ALIGNMENT			// FileAlignment
+	.short	0					// MajorOperatingSystemVersion
+	.short	0					// MinorOperatingSystemVersion
+	.short	LINUX_EFISTUB_MAJOR_VERSION		// MajorImageVersion
+	.short	LINUX_EFISTUB_MINOR_VERSION		// MinorImageVersion
+	.short	0					// MajorSubsystemVersion
+	.short	0					// MinorSubsystemVersion
+	.long	0					// Win32VersionValue
+
+	.long	_end - _start				// SizeOfImage
+
+	// Everything before the kernel image is considered part of the header
+	.long	efi_header_end - _start			// SizeOfHeaders
+	.long	0					// CheckSum
+	.short	IMAGE_SUBSYSTEM_EFI_APPLICATION		// Subsystem
+	.short	0					// DllCharacteristics
+	.quad	0					// SizeOfStackReserve
+	.quad	0					// SizeOfStackCommit
+	.quad	0					// SizeOfHeapReserve
+	.quad	0					// SizeOfHeapCommit
+	.long	0					// LoaderFlags
+	.long	(section_table - .) / 8			// NumberOfRvaAndSizes
+
+	.quad	0					// ExportTable
+	.quad	0					// ImportTable
+	.quad	0					// ResourceTable
+	.quad	0					// ExceptionTable
+	.quad	0					// CertificationTable
+	.quad	0					// BaseRelocationTable
+
+	// Section table
+section_table:
+	.ascii	".text\0\0\0"
+	.long	__pecoff_text_end - efi_header_end	// VirtualSize
+	.long	efi_header_end - _start			// VirtualAddress
+	.long	__pecoff_text_end - efi_header_end	// SizeOfRawData
+	.long	efi_header_end - _start			// PointerToRawData
+
+	.long	0					// PointerToRelocations
+	.long	0					// PointerToLineNumbers
+	.short	0					// NumberOfRelocations
+	.short	0					// NumberOfLineNumbers
+	.long	IMAGE_SCN_CNT_CODE | \
+		IMAGE_SCN_MEM_READ | \
+		IMAGE_SCN_MEM_EXECUTE			// Characteristics
+
+	.ascii	".data\0\0\0"
+	.long	__pecoff_data_virt_size			// VirtualSize
+	.long	__pecoff_text_end - _start		// VirtualAddress
+	.long	__pecoff_data_raw_size			// SizeOfRawData
+	.long	__pecoff_text_end - _start		// PointerToRawData
+
+	.long	0					// PointerToRelocations
+	.long	0					// PointerToLineNumbers
+	.short	0					// NumberOfRelocations
+	.short	0					// NumberOfLineNumbers
+	.long	IMAGE_SCN_CNT_INITIALIZED_DATA | \
+		IMAGE_SCN_MEM_READ | \
+		IMAGE_SCN_MEM_WRITE			// Characteristics
+
+	.set	section_count, (. - section_table) / 40
+
+	.balign	0x1000
+efi_header_end:
+	.endm
diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
index 98a406474e7d..c31d32e81d39 100644
--- a/arch/riscv/kernel/head.S
+++ b/arch/riscv/kernel/head.S
@@ -13,6 +13,7 @@
 #include <asm/csr.h>
 #include <asm/hwcap.h>
 #include <asm/image.h>
+#include "efi-header.S"
 
 __HEAD
 ENTRY(_start)
@@ -22,10 +23,18 @@ ENTRY(_start)
 	 * Do not modify it without modifying the structure and all bootloaders
 	 * that expects this header format!!
 	 */
+#ifdef CONFIG_EFI
+	/*
+	 * This instruction decodes to "MZ" ASCII required by UEFI.
+	 */
+	c.li s4,-13
+	j _start_kernel
+#else
 	/* jump to start kernel */
 	j _start_kernel
 	/* reserved */
 	.word 0
+#endif
 	.balign 8
 #if __riscv_xlen == 64
 	/* Image load offset(2MB) from start of RAM */
@@ -43,7 +52,14 @@ ENTRY(_start)
 	.ascii RISCV_IMAGE_MAGIC
 	.balign 4
 	.ascii RISCV_IMAGE_MAGIC2
+#ifdef CONFIG_EFI
+	.word pe_head_start - _start
+pe_head_start:
+
+	__EFI_PE_HEADER
+#else
 	.word 0
+#endif
 
 .align 2
 #ifdef CONFIG_MMU
diff --git a/arch/riscv/kernel/image-vars.h b/arch/riscv/kernel/image-vars.h
new file mode 100644
index 000000000000..bd8b764f0ad9
--- /dev/null
+++ b/arch/riscv/kernel/image-vars.h
@@ -0,0 +1,53 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2020 Western Digital Corporation or its affiliates.
+ * Linker script variables to be set after section resolution, as
+ * ld.lld does not like variables assigned before SECTIONS is processed.
+ * Based on arch/arm64/kerne/image-vars.h
+ */
+#ifndef __RISCV_KERNEL_IMAGE_VARS_H
+#define __RISCV_KERNEL_IMAGE_VARS_H
+
+#ifndef LINKER_SCRIPT
+#error This file should only be included in vmlinux.lds.S
+#endif
+
+#ifdef CONFIG_EFI
+
+__efistub_stext_offset = _start_kernel - _start;
+
+/*
+ * The EFI stub has its own symbol namespace prefixed by __efistub_, to
+ * isolate it from the kernel proper. The following symbols are legally
+ * accessed by the stub, so provide some aliases to make them accessible.
+ * Only include data symbols here, or text symbols of functions that are
+ * guaranteed to be safe when executed at another offset than they were
+ * linked at. The routines below are all implemented in assembler in a
+ * position independent manner
+ */
+__efistub_memcmp		= memcmp;
+__efistub_memchr		= memchr;
+__efistub_memcpy		= memcpy;
+__efistub_memmove		= memmove;
+__efistub_memset		= memset;
+__efistub_strlen		= strlen;
+__efistub_strnlen		= strnlen;
+__efistub_strcmp		= strcmp;
+__efistub_strncmp		= strncmp;
+__efistub_strrchr		= strrchr;
+
+#ifdef CONFIG_KASAN
+__efistub___memcpy		= memcpy;
+__efistub___memmove		= memmove;
+__efistub___memset		= memset;
+#endif
+
+__efistub__start		= _start;
+__efistub__start_kernel		= _start_kernel;
+__efistub__end			= _end;
+__efistub__edata		= _edata;
+__efistub_screen_info		= screen_info;
+
+#endif
+
+#endif /* __RISCV_KERNEL_IMAGE_VARS_H */
diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
index 0339b6bbe11a..ae22057a3f55 100644
--- a/arch/riscv/kernel/vmlinux.lds.S
+++ b/arch/riscv/kernel/vmlinux.lds.S
@@ -10,6 +10,7 @@
 #include <asm/cache.h>
 #include <asm/thread_info.h>
 #include <asm/set_memory.h>
+#include "image-vars.h"
 
 #include <linux/sizes.h>
 OUTPUT_ARCH(riscv)
@@ -17,6 +18,9 @@ ENTRY(_start)
 
 jiffies = jiffies_64;
 
+PECOFF_SECTION_ALIGNMENT = 0x1000;
+PECOFF_FILE_ALIGNMENT = 0x200;
+
 SECTIONS
 {
 	/* Beginning of code and text segment */
@@ -71,6 +75,10 @@ SECTIONS
 
 	EXCEPTION_TABLE(0x10)
 
+#ifdef CONFIG_EFI
+	. = ALIGN(PECOFF_SECTION_ALIGNMENT);
+	__pecoff_text_end = .;
+#endif
 	. = ALIGN(SECTION_ALIGN);
 	_data = .;
 
@@ -78,16 +86,26 @@ SECTIONS
 	.sdata : {
 		__global_pointer$ = . + 0x800;
 		*(.sdata*)
-		/* End of data section */
-		_edata = .;
 	}
 
+#ifdef CONFIG_EFI
+	.pecoff_edata_padding : { BYTE(0); . = ALIGN(PECOFF_FILE_ALIGNMENT); }
+	__pecoff_data_raw_size = ABSOLUTE(. - __pecoff_text_end);
+#endif
+
+	/* End of data section */
+	_edata = .;
+
 	BSS_SECTION(PAGE_SIZE, PAGE_SIZE, 0)
 
 	.rel.dyn : {
 		*(.rel.dyn*)
 	}
 
+#ifdef CONFIG_EFI
+	. = ALIGN(PECOFF_SECTION_ALIGNMENT);
+	__pecoff_data_virt_size = ABSOLUTE(. - __pecoff_text_end);
+#endif
 	_end = .;
 
 	STABS_DEBUG
-- 
2.17.1