Re: [PATCH v6 5/9] RISC-V: Add PE/COFF header for EFI stub

[Atish Patra <atishp@atishpatra.org>]

On Tue, Aug 25, 2020 at 11:04 AM Palmer Dabbelt <palmer@dabbelt.com> wrote:
>
> On Wed, 19 Aug 2020 15:24:21 PDT (-0700), Atish Patra 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>
> > 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>
> > Reviewed-by: Anup Patel <anup@brainfault.org>
> > ---
> >  arch/riscv/include/asm/sections.h |  13 ++++
> >  arch/riscv/kernel/Makefile        |   4 ++
> >  arch/riscv/kernel/efi-header.S    | 104 ++++++++++++++++++++++++++++++
> >  arch/riscv/kernel/head.S          |  16 +++++
> >  arch/riscv/kernel/image-vars.h    |  51 +++++++++++++++
> >  arch/riscv/kernel/vmlinux.lds.S   |  22 ++++++-
> >  6 files changed, 208 insertions(+), 2 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/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 a5287ab9f7f2..eabec4dce50b 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)
> > +
>
> Is there a reason this is below those objects?
Nope.

  I don't really care, but it
> triggered a merge conflict and it seems cleaner above so I put it up there.
>

Sure. Thanks.

> >  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..822b4c9ff2bb
> > --- /dev/null
> > +++ b/arch/riscv/kernel/efi-header.S
> > @@ -0,0 +1,104 @@
> > +/* 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:
> > +#ifdef CONFIG_64BIT
> > +     .short  IMAGE_FILE_MACHINE_RISCV64              // Machine
> > +#else
> > +     .short  IMAGE_FILE_MACHINE_RISCV32              // Machine
> > +#endif
> > +     .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_pe_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 c6a37e8231a8..3631147732ee 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..8c212efb37a6
> > --- /dev/null
> > +++ b/arch/riscv/kernel/image-vars.h
> > @@ -0,0 +1,51 @@
> > +/* 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
> > +
> > +/*
> > + * 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 f3586e31ed1e..6dcf790282dd 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 */
> > @@ -76,6 +80,10 @@ SECTIONS
> >
> >       EXCEPTION_TABLE(0x10)
> >
> > +#ifdef CONFIG_EFI
> > +     . = ALIGN(PECOFF_SECTION_ALIGNMENT);
> > +     __pecoff_text_end = .;
> > +#endif
> >       . = ALIGN(SECTION_ALIGN);
> >       _data = .;
> >
> > @@ -83,16 +91,26 @@ 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



-- 
Regards,
Atish