Re: [PATCH v4 15/26] efi/x86: Support extracting kernel from libstub

[Evgeniy Baskov]

On 2023-03-09 19:49, Ard Biesheuvel wrote:
> On Thu, 15 Dec 2022 at 13:40, Evgeniy Baskov <baskov@xxxxxxxxx> wrote:
> > Doing it that way allows setting up stricter memory attributes,
> > simplifies boot code path and removes potential relocation
> > of kernel image.
> >
> > Wire up required interfaces and minimally initialize zero page
> > fields needed for it to function correctly.
> >
> > Tested-by: Peter Jones <pjones@xxxxxxxxxx>
> > Signed-off-by: Evgeniy Baskov <baskov@xxxxxxxxx>
>
> OK I just realized that there is a problem with this approach: since
> we now decompress the image while running in the EFI stub (i.e.,
> before ExitBootServices()), we cannot just randomly pick a
> EFI_CONVENTIONAL_MEMORY region to place the kernel, we need to
> allocate the pages using the boot services. Otherwise, subsequent
> allocations (or concurrent ones occurring in the firmware in event
> handlers etc) may land right in the middle, which is unlikely to be
> what we want.

It does allocate pages for the kernel.
I've marked the place below.

> > ---
> >  arch/x86/boot/compressed/head_32.S            |  50 ++++-
> >  arch/x86/boot/compressed/head_64.S            |  58 ++++-
> >  drivers/firmware/efi/Kconfig                  |   2 +
> >  drivers/firmware/efi/libstub/Makefile         |   2 +-
> >  .../firmware/efi/libstub/x86-extract-direct.c | 208 
> > ++++++++++++++++++
> >  drivers/firmware/efi/libstub/x86-stub.c       | 119 +---------
> >  drivers/firmware/efi/libstub/x86-stub.h       |  14 ++
> >  7 files changed, 338 insertions(+), 115 deletions(-)
> >  create mode 100644 drivers/firmware/efi/libstub/x86-extract-direct.c
> >  create mode 100644 drivers/firmware/efi/libstub/x86-stub.h
> >
> > diff --git a/arch/x86/boot/compressed/head_32.S 
> > b/arch/x86/boot/compressed/head_32.S
> > index ead6007df1e5..0be75e5072ae 100644
> > --- a/arch/x86/boot/compressed/head_32.S
> > +++ b/arch/x86/boot/compressed/head_32.S
> > @@ -152,11 +152,57 @@ SYM_FUNC_END(startup_32)
> >
> >  #ifdef CONFIG_EFI_STUB
> >  SYM_FUNC_START(efi32_stub_entry)
> > +/*
> > + * Calculate the delta between where we were compiled to run
> > + * at and where we were actually loaded at.  This can only be done
> > + * with a short local call on x86.  Nothing  else will tell us what
> > + * address we are running at.  The reserved chunk of the real-mode
> > + * data at 0x1e4 (defined as a scratch field) are used as the stack
> > + * for this calculation. Only 4 bytes are needed.
> > + */
> > +       call    1f
> > +1:     popl    %ebx
> > +       addl    $_GLOBAL_OFFSET_TABLE_+(.-1b), %ebx
> > +
> > +       /* Clear BSS */
> > +       xorl    %eax, %eax
> > +       leal    _bss@GOTOFF(%ebx), %edi
> > +       leal    _ebss@GOTOFF(%ebx), %ecx
> > +       subl    %edi, %ecx
> > +       shrl    $2, %ecx
> > +       rep     stosl
> > +
> >         add     $0x4, %esp
> >         movl    8(%esp), %esi   /* save boot_params pointer */
> > +       movl    %edx, %edi      /* save GOT address */
> >         call    efi_main
> > -       /* efi_main returns the possibly relocated address of 
> > startup_32 */
> > -       jmp     *%eax
> > +       movl    %eax, %ecx
> > +
> > +       /*
> > +        * efi_main returns the possibly
> > +        * relocated address of extracted kernel entry point.
> > +        */
> > +
> > +       cli
> > +
> > +       /* Load new GDT */
> > +       leal    gdt@GOTOFF(%ebx), %eax
> > +       movl    %eax, 2(%eax)
> > +       lgdt    (%eax)
> > +
> > +       /* Load segment registers with our descriptors */
> > +       movl    $__BOOT_DS, %eax
> > +       movl    %eax, %ds
> > +       movl    %eax, %es
> > +       movl    %eax, %fs
> > +       movl    %eax, %gs
> > +       movl    %eax, %ss
> > +
> > +       /* Zero EFLAGS */
> > +       pushl   $0
> > +       popfl
> > +
> > +       jmp     *%ecx
> >  SYM_FUNC_END(efi32_stub_entry)
> >  SYM_FUNC_ALIAS(efi_stub_entry, efi32_stub_entry)
> >  #endif
> > diff --git a/arch/x86/boot/compressed/head_64.S 
> > b/arch/x86/boot/compressed/head_64.S
> > index 2dd8be0583d2..7cfef7bd0424 100644
> > --- a/arch/x86/boot/compressed/head_64.S
> > +++ b/arch/x86/boot/compressed/head_64.S
> > @@ -529,12 +529,64 @@ SYM_CODE_END(startup_64)
> >         .org 0x390
> >  #endif
> >  SYM_FUNC_START(efi64_stub_entry)
> > +       /* Preserve first parameter */
> > +       movq    %rdi, %r10
> > +
> > +       /* Clear BSS */
> > +       xorl    %eax, %eax
> > +       leaq    _bss(%rip), %rdi
> > +       leaq    _ebss(%rip), %rcx
> > +       subq    %rdi, %rcx
> > +       shrq    $3, %rcx
> > +       rep     stosq
> > +
> >         and     $~0xf, %rsp                     /* realign the stack 
> > */
> >         movq    %rdx, %rbx                      /* save boot_params 
> > pointer */
> > +       movq    %r10, %rdi
> >         call    efi_main
> > -       movq    %rbx,%rsi
> > -       leaq    rva(startup_64)(%rax), %rax
> > -       jmp     *%rax
> > +
> > +       cld
> > +       cli
> > +
> > +       movq    %rbx, %rdi /* boot_params */
> > +       movq    %rax, %rsi /* decompressed kernel address */
> > +
> > +       /* Make sure we have GDT with 32-bit code segment */
> > +       leaq    gdt64(%rip), %rax
> > +       addq    %rax, 2(%rax)
> > +       lgdt    (%rax)
> > +
> > +       /* Setup data segments. */
> > +       xorl    %eax, %eax
> > +       movl    %eax, %ds
> > +       movl    %eax, %es
> > +       movl    %eax, %ss
> > +       movl    %eax, %fs
> > +       movl    %eax, %gs
> > +
> > +       pushq   %rsi
> > +       pushq   %rdi
> > +
> > +       call    load_stage1_idt
> > +       call    enable_nx_if_supported
> > +
> > +       call    trampoline_pgtable_init
> > +       movq    %rax, %rdx
> > +
> > +
> > +       /* Swap %rsi and %rsi */
> > +       popq    %rsi
> > +       popq    %rdi
> > +
> > +       /* Save the trampoline address in RCX */
> > +       movq    trampoline_32bit(%rip), %rcx
> > +
> > +       /* Switch to compatibility mode (CS.L = 0 CS.D = 1) via far 
> > return */
> > +       pushq   $__KERNEL32_CS
> > +       leaq    TRAMPOLINE_32BIT_CODE_OFFSET(%rcx), %rax
> > +       pushq   %rax
> > +       lretq
> > +
> >  SYM_FUNC_END(efi64_stub_entry)
> >  SYM_FUNC_ALIAS(efi_stub_entry, efi64_stub_entry)
> >  #endif
> > diff --git a/drivers/firmware/efi/Kconfig 
> > b/drivers/firmware/efi/Kconfig
> > index 043ca31c114e..f50c2a84a754 100644
> > --- a/drivers/firmware/efi/Kconfig
> > +++ b/drivers/firmware/efi/Kconfig
> > @@ -58,6 +58,8 @@ config EFI_DXE_MEM_ATTRIBUTES
> >           Use DXE services to check and alter memory protection
> >           attributes during boot via EFISTUB to ensure that memory
> >           ranges used by the kernel are writable and executable.
> > +         This option also enables stricter memory attributes
> > +         on compressed kernel PE image.
> >
> >  config EFI_PARAMS_FROM_FDT
> >         bool
> > diff --git a/drivers/firmware/efi/libstub/Makefile 
> > b/drivers/firmware/efi/libstub/Makefile
> > index be8b8c6e8b40..99b81c95344c 100644
> > --- a/drivers/firmware/efi/libstub/Makefile
> > +++ b/drivers/firmware/efi/libstub/Makefile
> > @@ -88,7 +88,7 @@ lib-$(CONFIG_EFI_GENERIC_STUB)        += efi-stub.o 
> > string.o intrinsics.o systable.o \
> >
> >  lib-$(CONFIG_ARM)              += arm32-stub.o
> >  lib-$(CONFIG_ARM64)            += arm64.o arm64-stub.o arm64-entry.o 
> > smbios.o
> > -lib-$(CONFIG_X86)              += x86-stub.o
> > +lib-$(CONFIG_X86)              += x86-stub.o x86-extract-direct.o
> >  lib-$(CONFIG_RISCV)            += riscv.o riscv-stub.o
> >  lib-$(CONFIG_LOONGARCH)                += loongarch.o 
> > loongarch-stub.o
> >
> > diff --git a/drivers/firmware/efi/libstub/x86-extract-direct.c 
> > b/drivers/firmware/efi/libstub/x86-extract-direct.c
> > new file mode 100644
> > index 000000000000..4ecbc4a9b3ed
> > --- /dev/null
> > +++ b/drivers/firmware/efi/libstub/x86-extract-direct.c
> > @@ -0,0 +1,208 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +
> > +#include <linux/acpi.h>
> > +#include <linux/efi.h>
> > +#include <linux/elf.h>
> > +#include <linux/stddef.h>
> > +
> > +#include <asm/efi.h>
> > +#include <asm/e820/types.h>
> > +#include <asm/desc.h>
> > +#include <asm/boot.h>
> > +#include <asm/bootparam_utils.h>
> > +#include <asm/shared/extract.h>
> > +#include <asm/shared/pgtable.h>
> > +
> > +#include "efistub.h"
> > +#include "x86-stub.h"
> > +
> > +static efi_handle_t image_handle;
> > +
> > +static void do_puthex(unsigned long value)
> > +{
> > +       efi_printk("%08lx", value);
> > +}
> > +
> > +static void do_putstr(const char *msg)
> > +{
> > +       efi_printk("%s", msg);
> > +}
> > +
> > +static unsigned long do_map_range(unsigned long start,
> > +                                 unsigned long end,
> > +                                 unsigned int flags)
> > +{
> > +       efi_status_t status;
> > +
> > +       unsigned long size = end - start;
> > +
> > +       if (flags & MAP_ALLOC) {
> > +               unsigned long addr;
> > +
> > +               status = efi_low_alloc_above(size, 
> > CONFIG_PHYSICAL_ALIGN,
> > +                                            &addr, start);

Memory for the kernel image is allocated here.
This function is getting called from the boot/compressed/misc.c with 
MAP_ALLOC flag
when the address for the kernel is picked.

> > +               if (status != EFI_SUCCESS) {
> > +                       efi_err("Unable to allocate memory for 
> > uncompressed kernel");
> > +                       efi_exit(image_handle, EFI_OUT_OF_RESOURCES);
> > +               }
> > +
> > +               if (start != addr) {
> > +                       efi_debug("Unable to allocate at given 
> > address"
> > +                                 " (desired=0x%lx, actual=0x%lx)",
> > +                                 (unsigned long)start, addr);
> > +                       start = addr;
> > +               }
> > +       }
> > +
> > +       if ((flags & (MAP_PROTECT | MAP_ALLOC)) &&
> > +           IS_ENABLED(CONFIG_EFI_DXE_MEM_ATTRIBUTES)) {
> > +               unsigned long attr = 0;
> > +
> > +               if (!(flags & MAP_EXEC))
> > +                       attr |= EFI_MEMORY_XP;
> > +
> > +               if (!(flags & MAP_WRITE))
> > +                       attr |= EFI_MEMORY_RO;
> > +
> > +               status = efi_adjust_memory_range_protection(start, 
> > size, attr);
> > +               if (status != EFI_SUCCESS)
> > +                       efi_err("Unable to protect memory range");
> > +       }
> > +
> > +       return start;
> > +}
> > +
> > +/*
> > + * Trampoline takes 3 pages and can be loaded in first megabyte of 
> > memory
> > + * with its end placed between 0 and 640k where BIOS might start.
> > + * (see arch/x86/boot/compressed/pgtable_64.c)
> > + */
> > +
> > +#ifdef CONFIG_64BIT
> > +static efi_status_t prepare_trampoline(void)
> > +{
> > +       efi_status_t status;
> > +
> > +       status = efi_allocate_pages(TRAMPOLINE_32BIT_SIZE,
> > +                                   (unsigned long 
> > *)&trampoline_32bit,
> > +                                   TRAMPOLINE_32BIT_PLACEMENT_MAX);
> > +
> > +       if (status != EFI_SUCCESS)
> > +               return status;
> > +
> > +       unsigned long trampoline_start = (unsigned 
> > long)trampoline_32bit;
> > +
> > +       memset(trampoline_32bit, 0, TRAMPOLINE_32BIT_SIZE);
> > +
> > +       if (IS_ENABLED(CONFIG_EFI_DXE_MEM_ATTRIBUTES)) {
> > +               /* First page of trampoline is a top level page table 
> > */
> > +               efi_adjust_memory_range_protection(trampoline_start,
> > +                                                  PAGE_SIZE,
> > +                                                  EFI_MEMORY_XP);
> > +       }
> > +
> > +       /* Second page of trampoline is the code (with a padding) */
> > +
> > +       void *caddr = (void *)trampoline_32bit + 
> > TRAMPOLINE_32BIT_CODE_OFFSET;
> > +
> > +       memcpy(caddr, trampoline_32bit_src, 
> > TRAMPOLINE_32BIT_CODE_SIZE);
> > +
> > +       if (IS_ENABLED(CONFIG_EFI_DXE_MEM_ATTRIBUTES)) {
> > +               efi_adjust_memory_range_protection((unsigned 
> > long)caddr,
> > +                                                  PAGE_SIZE,
> > +                                                  EFI_MEMORY_RO);
> > +
> > +               /* And the last page of trampoline is the stack */
> > +
> > +               efi_adjust_memory_range_protection(trampoline_start + 
> > 2 * PAGE_SIZE,
> > +                                                  PAGE_SIZE,
> > +                                                  EFI_MEMORY_XP);
> > +       }
> > +
> > +       return EFI_SUCCESS;
> > +}
> > +#else
> > +static inline efi_status_t prepare_trampoline(void)
> > +{
> > +       return EFI_SUCCESS;
> > +}
> > +#endif
> > +
> > +static efi_status_t init_loader_data(efi_handle_t handle,
> > +                                    struct boot_params *params,
> > +                                    struct efi_boot_memmap **map)
> > +{
> > +       struct efi_info *efi = (void *)&params->efi_info;
> > +       efi_status_t status;
> > +
> > +       status = efi_get_memory_map(map, false);
> > +
> > +       if (status != EFI_SUCCESS) {
> > +               efi_err("Unable to get EFI memory map...\n");
> > +               return status;
> > +       }
> > +
> > +       const char *signature = efi_is_64bit() ? 
> > EFI64_LOADER_SIGNATURE
> > +                                              : 
> > EFI32_LOADER_SIGNATURE;
> > +
> > +       memcpy(&efi->efi_loader_signature, signature, sizeof(__u32));
> > +
> > +       efi->efi_memdesc_size = (*map)->desc_size;
> > +       efi->efi_memdesc_version = (*map)->desc_ver;
> > +       efi->efi_memmap_size = (*map)->map_size;
> > +
> > +       efi_set_u64_split((unsigned long)(*map)->map,
> > +                         &efi->efi_memmap, &efi->efi_memmap_hi);
> > +
> > +       efi_set_u64_split((unsigned long)efi_system_table,
> > +                         &efi->efi_systab, &efi->efi_systab_hi);
> > +
> > +       image_handle = handle;
> > +
> > +       return EFI_SUCCESS;
> > +}
> > +
> > +static void free_loader_data(struct boot_params *params, struct 
> > efi_boot_memmap *map)
> > +{
> > +       struct efi_info *efi = (void *)&params->efi_info;
> > +
> > +       efi_bs_call(free_pool, map);
> > +
> > +       efi->efi_memdesc_size = 0;
> > +       efi->efi_memdesc_version = 0;
> > +       efi->efi_memmap_size = 0;
> > +       efi_set_u64_split(0, &efi->efi_memmap, &efi->efi_memmap_hi);
> > +}
> > +
> > +extern unsigned char input_data[];
> > +extern unsigned int input_len, output_len;
> > +
> > +unsigned long extract_kernel_direct(efi_handle_t handle, struct 
> > boot_params *params)
> > +{
> > +
> > +       void *res;
> > +       efi_status_t status;
> > +       struct efi_extract_callbacks cb = { 0 };
> > +
> > +       status = prepare_trampoline();
> > +
> > +       if (status != EFI_SUCCESS)
> > +               return 0;
> > +
> > +       /* Prepare environment for do_extract_kernel() call */
> > +       struct efi_boot_memmap *map = NULL;
> > +       status = init_loader_data(handle, params, &map);
> > +
> > +       if (status != EFI_SUCCESS)
> > +               return 0;
> > +
> > +       cb.puthex = do_puthex;
> > +       cb.putstr = do_putstr;
> > +       cb.map_range = do_map_range;
> > +
> > +       res = efi_extract_kernel(params, &cb, input_data, input_len, 
> > output_len);
> > +
> > +       free_loader_data(params, map);
> > +
> > +       return (unsigned long)res;
> > +}
> > diff --git a/drivers/firmware/efi/libstub/x86-stub.c 
> > b/drivers/firmware/efi/libstub/x86-stub.c
> > index 7fb1eff88a18..1d1ab1911fd3 100644
> > --- a/drivers/firmware/efi/libstub/x86-stub.c
> > +++ b/drivers/firmware/efi/libstub/x86-stub.c
> > @@ -17,6 +17,7 @@
> >  #include <asm/boot.h>
> >
> >  #include "efistub.h"
> > +#include "x86-stub.h"
> >
> >  /* Maximum physical address for 64-bit kernel with 4-level paging */
> >  #define MAXMEM_X86_64_4LEVEL (1ull << 46)
> > @@ -24,7 +25,7 @@
> >  const efi_system_table_t *efi_system_table;
> >  const efi_dxe_services_table_t *efi_dxe_table;
> >  u32 image_offset __section(".data");
> > -static efi_loaded_image_t *image = NULL;
> > +static efi_loaded_image_t *image __section(".data");
> >
> >  static efi_status_t
> >  preserve_pci_rom_image(efi_pci_io_protocol_t *pci, struct 
> > pci_setup_rom **__rom)
> > @@ -212,55 +213,9 @@ static void 
> > retrieve_apple_device_properties(struct boot_params *boot_params)
> >         }
> >  }
> >
> > -/*
> > - * Trampoline takes 2 pages and can be loaded in first megabyte of 
> > memory
> > - * with its end placed between 128k and 640k where BIOS might start.
> > - * (see arch/x86/boot/compressed/pgtable_64.c)
> > - *
> > - * We cannot find exact trampoline placement since memory map
> > - * can be modified by UEFI, and it can alter the computed address.
> > - */
> > -
> > -#define TRAMPOLINE_PLACEMENT_BASE ((128 - 8)*1024)
> > -#define TRAMPOLINE_PLACEMENT_SIZE (640*1024 - (128 - 8)*1024)
> > -
> > -void startup_32(struct boot_params *boot_params);
> > -
> > -static void
> > -setup_memory_protection(unsigned long image_base, unsigned long 
> > image_size)
> > -{
> > -       /*
> > -        * Allow execution of possible trampoline used
> > -        * for switching between 4- and 5-level page tables
> > -        * and relocated kernel image.
> > -        */
> > -
> > -       efi_adjust_memory_range_protection(TRAMPOLINE_PLACEMENT_BASE,
> > -                                          TRAMPOLINE_PLACEMENT_SIZE, 
> > 0);
> > -
> > -#ifdef CONFIG_64BIT
> > -       if (image_base != (unsigned long)startup_32)
> > -               efi_adjust_memory_range_protection(image_base, 
> > image_size, 0);
> > -#else
> > -       /*
> > -        * Clear protection flags on a whole range of possible
> > -        * addresses used for KASLR. We don't need to do that
> > -        * on x86_64, since KASLR/extraction is performed after
> > -        * dedicated identity page tables are built and we only
> > -        * need to remove possible protection on relocated image
> > -        * itself disregarding further relocations.
> > -        */
> > -       efi_adjust_memory_range_protection(LOAD_PHYSICAL_ADDR,
> > -                                          KERNEL_IMAGE_SIZE - 
> > LOAD_PHYSICAL_ADDR,
> > -                                          0);
> > -#endif
> > -}
> > -
> >  static const efi_char16_t apple[] = L"Apple";
> >
> > -static void setup_quirks(struct boot_params *boot_params,
> > -                        unsigned long image_base,
> > -                        unsigned long image_size)
> > +static void setup_quirks(struct boot_params *boot_params)
> >  {
> >         efi_char16_t *fw_vendor = (efi_char16_t *)(unsigned long)
> >                 efi_table_attr(efi_system_table, fw_vendor);
> > @@ -269,9 +224,6 @@ static void setup_quirks(struct boot_params 
> > *boot_params,
> >                 if (IS_ENABLED(CONFIG_APPLE_PROPERTIES))
> >                         retrieve_apple_device_properties(boot_params);
> >         }
> > -
> > -       if (IS_ENABLED(CONFIG_EFI_DXE_MEM_ATTRIBUTES))
> > -               setup_memory_protection(image_base, image_size);
> >  }
> >
> >  /*
> > @@ -384,7 +336,7 @@ static void setup_graphics(struct boot_params 
> > *boot_params)
> >  }
> >
> >
> > -static void __noreturn efi_exit(efi_handle_t handle, efi_status_t 
> > status)
> > +void __noreturn efi_exit(efi_handle_t handle, efi_status_t status)
> >  {
> >         efi_bs_call(exit, handle, status, 0, NULL);
> >         for(;;)
> > @@ -707,8 +659,7 @@ static efi_status_t exit_boot(struct boot_params 
> > *boot_params, void *handle)
> >  }
> >
> >  /*
> > - * On success, we return the address of startup_32, which has 
> > potentially been
> > - * relocated by efi_relocate_kernel.
> > + * On success, we return extracted kernel entry point.
> >   * On failure, we exit to the firmware via efi_exit instead of 
> > returning.
> >   */
> >  asmlinkage unsigned long efi_main(efi_handle_t handle,
> > @@ -733,60 +684,6 @@ asmlinkage unsigned long efi_main(efi_handle_t 
> > handle,
> >                 efi_dxe_table = NULL;
> >         }
> >
> > -       /*
> > -        * If the kernel isn't already loaded at a suitable address,
> > -        * relocate it.
> > -        *
> > -        * It must be loaded above LOAD_PHYSICAL_ADDR.
> > -        *
> > -        * The maximum address for 64-bit is 1 << 46 for 4-level 
> > paging. This
> > -        * is defined as the macro MAXMEM, but unfortunately that is 
> > not a
> > -        * compile-time constant if 5-level paging is configured, so 
> > we instead
> > -        * define our own macro for use here.
> > -        *
> > -        * For 32-bit, the maximum address is complicated to figure 
> > out, for
> > -        * now use KERNEL_IMAGE_SIZE, which will be 512MiB, the same 
> > as what
> > -        * KASLR uses.
> > -        *
> > -        * Also relocate it if image_offset is zero, i.e. the kernel 
> > wasn't
> > -        * loaded by LoadImage, but rather by a bootloader that called 
> > the
> > -        * handover entry. The reason we must always relocate in this 
> > case is
> > -        * to handle the case of systemd-boot booting a unified kernel 
> > image,
> > -        * which is a PE executable that contains the bzImage and an 
> > initrd as
> > -        * COFF sections. The initrd section is placed after the 
> > bzImage
> > -        * without ensuring that there are at least init_size bytes 
> > available
> > -        * for the bzImage, and thus the compressed kernel's startup 
> > code may
> > -        * overwrite the initrd unless it is moved out of the way.
> > -        */
> > -
> > -       buffer_start = ALIGN(bzimage_addr - image_offset,
> > -                            hdr->kernel_alignment);
> > -       buffer_end = buffer_start + hdr->init_size;
> > -
> > -       if ((buffer_start < LOAD_PHYSICAL_ADDR)                        
> >       ||
> > -           (IS_ENABLED(CONFIG_X86_32) && buffer_end > 
> > KERNEL_IMAGE_SIZE)    ||
> > -           (IS_ENABLED(CONFIG_X86_64) && buffer_end > 
> > MAXMEM_X86_64_4LEVEL) ||
> > -           (image_offset == 0)) {
> > -               extern char _bss[];
> > -
> > -               status = efi_relocate_kernel(&bzimage_addr,
> > -                                            (unsigned long)_bss - 
> > bzimage_addr,
> > -                                            hdr->init_size,
> > -                                            hdr->pref_address,
> > -                                            hdr->kernel_alignment,
> > -                                            LOAD_PHYSICAL_ADDR);
> > -               if (status != EFI_SUCCESS) {
> > -                       efi_err("efi_relocate_kernel() failed!\n");
> > -                       goto fail;
> > -               }
> > -               /*
> > -                * Now that we've copied the kernel elsewhere, we no 
> > longer
> > -                * have a set up block before startup_32(), so reset 
> > image_offset
> > -                * to zero in case it was set earlier.
> > -                */
> > -               image_offset = 0;
> > -       }
> > -
> >  #ifdef CONFIG_CMDLINE_BOOL
> >         status = efi_parse_options(CONFIG_CMDLINE);
> >         if (status != EFI_SUCCESS) {
> > @@ -843,7 +740,11 @@ asmlinkage unsigned long efi_main(efi_handle_t 
> > handle,
> >
> >         setup_efi_pci(boot_params);
> >
> > -       setup_quirks(boot_params, bzimage_addr, buffer_end - 
> > buffer_start);
> > +       setup_quirks(boot_params);
> > +
> > +       bzimage_addr = extract_kernel_direct(handle, boot_params);
> > +       if (!bzimage_addr)
> > +               goto fail;
> >
> >         status = exit_boot(boot_params, handle);
> >         if (status != EFI_SUCCESS) {
> > diff --git a/drivers/firmware/efi/libstub/x86-stub.h 
> > b/drivers/firmware/efi/libstub/x86-stub.h
> > new file mode 100644
> > index 000000000000..baecc7c6e602
> > --- /dev/null
> > +++ b/drivers/firmware/efi/libstub/x86-stub.h
> > @@ -0,0 +1,14 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +
> > +#ifndef _DRIVERS_FIRMWARE_EFI_X86STUB_H
> > +#define _DRIVERS_FIRMWARE_EFI_X86STUB_H
> > +
> > +#include <linux/efi.h>
> > +
> > +#include <asm/bootparam.h>
> > +
> > +void __noreturn efi_exit(efi_handle_t handle, efi_status_t status);
> > +unsigned long extract_kernel_direct(efi_handle_t handle, struct 
> > boot_params *boot_params);
> > +void startup_32(struct boot_params *boot_params);
> > +
> > +#endif
> > --
> > 2.37.4