Commit 17054f49 authored by Ard Biesheuvel's avatar Ard Biesheuvel
Browse files

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



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: default avatarArd Biesheuvel <ardb@kernel.org>
parent 3b8f44fc

arch/x86/boot/compressed/head_64.S

+57 −2
Original line number Diff line number Diff line
@@ -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



/*

drivers/firmware/efi/libstub/x86-stub.c

+16 −13
Original line number Diff line number Diff line
@@ -424,12 +424,14 @@ efi_status_t __efiapi efi_pe_entry(efi_handle_t handle, 
	hdr->ramdisk_image = 0;

	hdr->ramdisk_size = 0;



	if (efi_is_native()) {

		status = efi_parse_options(cmdline_ptr);

		if (status != EFI_SUCCESS)

			goto fail2;



		if (!noinitrd()) {

		status = efi_load_initrd(image, &ramdisk_addr, &ramdisk_size,

			status = efi_load_initrd(image, &ramdisk_addr,

						 &ramdisk_size,

						 hdr->initrd_addr_max,

						 above4g ? ULONG_MAX

							 : hdr->initrd_addr_max);
@@ -440,6 +442,7 @@ efi_status_t __efiapi efi_pe_entry(efi_handle_t handle, 
			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);

	/* not reached */

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