Re: [RFC PATCH 4/5] RISC-V: Add PE/COFF header for EFI stub

From: Ard Biesheuvel
Date: Thu Feb 27 2020 - 02:49:01 EST

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On Thu, 27 Feb 2020 at 02:29, Atish Patra <Atish.Patra@xxxxxxx> wrote:
>
> On Wed, 2020-02-26 at 08:14 +0100, Ard Biesheuvel wrote:
> > On Wed, 26 Feb 2020 at 02:10, Atish Patra <atish.patra@xxxxxxx>
> > 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@xxxxxxx>
> > > ---
> > > 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
> >
>
> Sure.
>
> > > + .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.
> >
>
> Ahh I see. I was not sure how to use the debug feature :). Can we do
> the same in U-boot ?
>

You could, but I doubt it has been implemented yet.

Adding the debug header will cause the firmware to record the image
path and its load address in a special debug table, which the firmware
can use to expose the load address and path of the image as it is
loaded (i.e. before moving itself into place)

When I run this under a DEBUG build of EDK2, it prints a line like

add-symbol-file /home/ardbie01/linux-build-arm64/vmlinux 0x74E0B000

which I can paste into the GDB command window, set a breakpoint on
efi_entry(), and single step through the stub.

> How about adding it back later once I can verify it with EDK2 ?
>

Sure, that is fine

> > > + /*
> > > + * 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?
>
> Sorry. I should have removed the comment. We keep the the _start and
> .head.text section aligned to a PAGE_SIZE anyways using the linker
> script.

ok

> >
> > > + * 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.
> >
>
> There should have been a "j _start_kernel" after the "MZ" ascii. I just
> tested EFI kernel can now boot as a normal kernel as well with that
> change. Thanks for pointing that out.
>

Sure

> > > +#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
> > >
>
> --
> Regards,
> Atish

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Next in thread: Atish Patra: "[RFC PATCH 5/5] RISC-V: Add EFI stub support."
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