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efi/x86: Implement mixed mode boot without the handover protocol

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Add support for booting 64-bit x86 kernels from 32-bit firmware running
on 64-bit capable CPUs without requiring the bootloader to implement
the EFI handover protocol or allocate the setup block, etc etc, all of
which can be done by the stub itself, using code that already exists.

Instead, create an ordinary EFI application entrypoint but implemented
in 32-bit code [so that it can be invoked by 32-bit firmware], and stash
the address of this 32-bit entrypoint in the .compat section where the
bootloader can find it.

Note that we use the setup block embedded in the binary to go through
startup_32(), but it gets reallocated and copied in efi_pe_entry(),
using the same code that runs when the x86 kernel is booted in EFI
mode from native firmware. This requires the loaded image protocol to
be installed on the kernel image's EFI handle, and point to the kernel
image itself and not to its loader. This, in turn, requires the
bootloader to use the LoadImage() boot service to load the 64-bit
image from 32-bit firmware, which is in fact supported by firmware
based on EDK2. (Only StartImage() will fail, and instead, the newly
added entrypoint needs to be invoked)

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
This commit is contained in:
Ard Biesheuvel 2020-02-12 23:20:54 +01:00
parent 3b8f44fc08
commit 17054f492d
2 changed files with 73 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

59
arch/x86/boot/compressed/head_64.S
View File

@ -207,8 +207,13 @@ SYM_FUNC_START(startup_32)
cmp $0, %edi
jz 1f
leal efi64_stub_entry(%ebp), %eax
movl %esi, %edx
movl efi32_boot_args+4(%ebp), %esi
movl efi32_boot_args+8(%ebp), %edx // saved bootparams pointer
cmpl $0, %edx
jnz 1f
leal efi_pe_entry(%ebp), %eax
movl %edi, %ecx // MS calling convention
movl %esi, %edx
1:
#endif
pushl %eax
@ -233,6 +238,8 @@ SYM_FUNC_START(efi32_stub_entry)
1: pop %ebp
subl $1b, %ebp
movl %esi, efi32_boot_args+8(%ebp)
SYM_INNER_LABEL(efi32_pe_stub_entry, SYM_L_LOCAL)
movl %ecx, efi32_boot_args(%ebp)
movl %edx, efi32_boot_args+4(%ebp)
movb $0, efi_is64(%ebp)
@ -641,8 +648,56 @@ SYM_DATA_START_LOCAL(gdt)
SYM_DATA_END_LABEL(gdt, SYM_L_LOCAL, gdt_end)
#ifdef CONFIG_EFI_MIXED
SYM_DATA_LOCAL(efi32_boot_args, .long 0, 0)
SYM_DATA_LOCAL(efi32_boot_args, .long 0, 0, 0)
SYM_DATA(efi_is64, .byte 1)
#define ST32_boottime 60 // offsetof(efi_system_table_32_t, boottime)
#define BS32_handle_protocol 88 // offsetof(efi_boot_services_32_t, handle_protocol)
#define LI32_image_base 32 // offsetof(efi_loaded_image_32_t, image_base)
.text
.code32
SYM_FUNC_START(efi32_pe_entry)
pushl %ebp
call verify_cpu // check for long mode support
testl %eax, %eax
movl $0x80000003, %eax // EFI_UNSUPPORTED
jnz 3f
call 1f
1: pop %ebp
subl $1b, %ebp
/* Get the loaded image protocol pointer from the image handle */
subl $12, %esp // space for the loaded image pointer
pushl %esp // pass its address
leal 4f(%ebp), %eax
pushl %eax // pass the GUID address
pushl 28(%esp) // pass the image handle
movl 36(%esp), %eax // sys_table
movl ST32_boottime(%eax), %eax // sys_table->boottime
call *BS32_handle_protocol(%eax) // sys_table->boottime->handle_protocol
cmp $0, %eax
jnz 2f
movl 32(%esp), %ecx // image_handle
movl 36(%esp), %edx // sys_table
movl 12(%esp), %esi // loaded_image
movl LI32_image_base(%esi), %esi // loaded_image->image_base
jmp efi32_pe_stub_entry
2: addl $24, %esp
3: popl %ebp
ret
SYM_FUNC_END(efi32_pe_entry)
.section ".rodata"
/* EFI loaded image protocol GUID */
4: .long 0x5B1B31A1
.word 0x9562, 0x11d2
.byte 0x8E, 0x3F, 0x00, 0xA0, 0xC9, 0x69, 0x72, 0x3B
#endif
/*

29
drivers/firmware/efi/libstub/x86-stub.c
View File

@ -424,21 +424,24 @@ efi_status_t __efiapi efi_pe_entry(efi_handle_t handle,
hdr->ramdisk_image = 0;
hdr->ramdisk_size = 0;
status = efi_parse_options(cmdline_ptr);
if (status != EFI_SUCCESS)
goto fail2;
if (!noinitrd()) {
status = efi_load_initrd(image, &ramdisk_addr, &ramdisk_size,
hdr->initrd_addr_max,
above4g ? ULONG_MAX
: hdr->initrd_addr_max);
if (efi_is_native()) {
status = efi_parse_options(cmdline_ptr);
if (status != EFI_SUCCESS)
goto fail2;
hdr->ramdisk_image = ramdisk_addr & 0xffffffff;
hdr->ramdisk_size = ramdisk_size & 0xffffffff;
boot_params->ext_ramdisk_image = (u64)ramdisk_addr >> 32;
boot_params->ext_ramdisk_size = (u64)ramdisk_size >> 32;
if (!noinitrd()) {
status = efi_load_initrd(image, &ramdisk_addr,
&ramdisk_size,
hdr->initrd_addr_max,
above4g ? ULONG_MAX
: hdr->initrd_addr_max);
if (status != EFI_SUCCESS)
goto fail2;
hdr->ramdisk_image = ramdisk_addr & 0xffffffff;
hdr->ramdisk_size = ramdisk_size & 0xffffffff;
boot_params->ext_ramdisk_image = (u64)ramdisk_addr >> 32;
boot_params->ext_ramdisk_size = (u64)ramdisk_size >> 32;
}
}
efi_stub_entry(handle, sys_table, boot_params);