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SubjectRe: [RFC PATCH 4/5] RISC-V: Add PE/COFF header for EFI stub
On Wed, 26 Feb 2020 at 02:10, Atish Patra <atish.patra@wdc.com> wrote:
>
> 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>
> ---
> arch/riscv/include/asm/Kbuild | 1 -
> arch/riscv/include/asm/sections.h | 13 ++++
> arch/riscv/kernel/Makefile | 4 ++
> arch/riscv/kernel/efi-header.S | 107 ++++++++++++++++++++++++++++++
> arch/riscv/kernel/head.S | 15 +++++
> arch/riscv/kernel/image-vars.h | 52 +++++++++++++++
> arch/riscv/kernel/vmlinux.lds.S | 27 ++++++--
> 7 files changed, 212 insertions(+), 7 deletions(-)
> create mode 100644 arch/riscv/include/asm/sections.h
> create mode 100644 arch/riscv/kernel/efi-header.S
> create mode 100644 arch/riscv/kernel/image-vars.h
>
> diff --git a/arch/riscv/include/asm/Kbuild b/arch/riscv/include/asm/Kbuild
> index 517394390106..ef797fe44934 100644
> --- a/arch/riscv/include/asm/Kbuild
> +++ b/arch/riscv/include/asm/Kbuild
> @@ -24,7 +24,6 @@ generic-y += local64.h
> generic-y += mm-arch-hooks.h
> generic-y += percpu.h
> generic-y += preempt.h
> -generic-y += sections.h
> generic-y += serial.h
> generic-y += shmparam.h
> generic-y += topology.h
> 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 9601ac907f70..471b1c73f77d 100644
> --- a/arch/riscv/kernel/Makefile
> +++ b/arch/riscv/kernel/Makefile
> @@ -29,6 +29,10 @@ obj-y += cacheinfo.o
> obj-$(CONFIG_MMU) += vdso.o vdso/
>
> obj-$(CONFIG_RISCV_M_MODE) += clint.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..af959e748d93
> --- /dev/null
> +++ b/arch/riscv/kernel/efi-header.S
> @@ -0,0 +1,107 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (C) 2019 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 __text_end - efi_header_end // SizeOfCode
> + .long _end - __text_end // SizeOfInitializedData
> + .long 0 // SizeOfUninitializedData
> + .long __efistub_efi_entry - _start // AddressOfEntryPoint
> + .long efi_header_end - _start // BaseOfCode
> +
> +extra_header_fields:
> + .quad 0 // ImageBase
> + .long SZ_4K // SectionAlignment
> + .long PECOFF_FILE_ALIGNMENT // FileAlignment
> + .short 0 // MajorOperatingSystemVersion
> + .short 0 // MinorOperatingSystemVersion
> + .short 0 // MajorImageVersion
> + .short 0 // MinorImageVersion

Put LINUX_EFISTUB_MAJOR_VERSION and LINUX_EFISTUB_MINOR_VERSION here

> + .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 __text_end - efi_header_end // VirtualSize
> + .long efi_header_end - _start // VirtualAddress
> + .long __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 __data_virt_size // VirtualSize
> + .long __text_end - _start // VirtualAddress
> + .long __data_raw_size // SizeOfRawData
> + .long __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
> +

You dropped the debug header here, which is actually *very* useful if
you want to single step through the stub from DEBUG edk2 firmware.

> + /*
> + * EFI will load .text onwards at the 4k section alignment
> + * described in the PE/COFF header. To ensure that instruction
> + * sequences using an adrp and a :lo12: immediate will function

Surely, this is inaccurate for RISC-V?

> + * correctly at this alignment, we must ensure that .text is
> + * placed at a 4k boundary in the Image to begin with.
> + */
> + .align 12
> +efi_header_end:
> + .endm
> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> index ac5b0e0a02f6..835dc76de285 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 +23,17 @@ 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.
> + */
> + li s4,-13

What happens if you try to do plain boot on an EFI kernel? On ARM and
x86, we took care to use a 'MZ' opcode that behaves as a pseudo-NOP,
and jump to start_kernel right after, so if you boot the EFI kernel as
a normal kernel, it still works.

> +#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 +51,14 @@ 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..57abb85065e9
> --- /dev/null
> +++ b/arch/riscv/kernel/image-vars.h
> @@ -0,0 +1,52 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * 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 b32640300d07..933b9e9a4b39 100644
> --- a/arch/riscv/kernel/vmlinux.lds.S
> +++ b/arch/riscv/kernel/vmlinux.lds.S
> @@ -9,6 +9,7 @@
> #include <asm/page.h>
> #include <asm/cache.h>
> #include <asm/thread_info.h>
> +#include "image-vars.h"
>
> #include <linux/sizes.h>
> OUTPUT_ARCH(riscv)
> @@ -16,6 +17,14 @@ ENTRY(_start)
>
> jiffies = jiffies_64;
>
> +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
> {
> /* Beginning of code and text segment */
> @@ -26,12 +35,15 @@ SECTIONS
>
> __init_begin = .;
> INIT_TEXT_SECTION(PAGE_SIZE)
> +
> + /* Start of data section */
> INIT_DATA_SECTION(16)
> /* we have to discard exit text and such at runtime, not link time */
> .exit.text :
> {
> EXIT_TEXT
> }
> +
> .exit.data :
> {
> EXIT_DATA
> @@ -54,7 +66,8 @@ SECTIONS
> _etext = .;
> }
>
> - /* Start of data section */
> + __text_end = .;
> +
> _sdata = .;
> RO_DATA(L1_CACHE_BYTES)
> .srodata : {
> @@ -65,19 +78,21 @@ SECTIONS
> .sdata : {
> __global_pointer$ = . + 0x800;
> *(.sdata*)
> - /* End of data section */
> - _edata = .;
> *(.sbss*)
> }
> -
> - BSS_SECTION(PAGE_SIZE, PAGE_SIZE, 0)
> -
> + PECOFF_EDATA_PADDING
> + __data_raw_size = ABSOLUTE(. - __text_end);
> + /* End of data section */
> + _edata = .;
> EXCEPTION_TABLE(0x10)
>
> .rel.dyn : {
> *(.rel.dyn*)
> }
>
> + BSS_SECTION(PAGE_SIZE, PAGE_SIZE, 0)
> + __data_virt_size = ABSOLUTE(. - __text_end);
> +
> _end = .;
>
> STABS_DEBUG
> --
> 2.24.0
>

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