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Message-ID: <CAMj1kXEF_FErDAz_URo-QjRtyxP1bC_YSz7bNcJ5Pypckds80A@mail.gmail.com>
Date: Thu, 9 Mar 2023 18:11:04 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: Evgeniy Baskov <baskov@...ras.ru>
Cc: Borislav Petkov <bp@...en8.de>, Andy Lutomirski <luto@...nel.org>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Alexey Khoroshilov <khoroshilov@...ras.ru>,
Peter Jones <pjones@...hat.com>,
"Limonciello, Mario" <mario.limonciello@....com>,
joeyli <jlee@...e.com>, lvc-project@...uxtesting.org,
x86@...nel.org, linux-efi@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v4 15/26] efi/x86: Support extracting kernel from libstub
On Thu, 9 Mar 2023 at 18:10, Evgeniy Baskov <baskov@...ras.ru> wrote:
>
> On 2023-03-09 19:49, Ard Biesheuvel wrote:
> > On Thu, 15 Dec 2022 at 13:40, Evgeniy Baskov <baskov@...ras.ru> 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@...hat.com>
> >> Signed-off-by: Evgeniy Baskov <baskov@...ras.ru>
> >
> > 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.
>
Ah excellent, thanks for clearing that up.
> >
> >
> >> ---
> >> 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@...OFF(%ebx), %edi
> >> + leal _ebss@...OFF(%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@...OFF(%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 *)¶ms->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 *)¶ms->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
> >>
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