x86, efi: Handover Protocol

As things currently stand, traditional EFI boot loaders and the EFI
boot stub are carrying essentially the same initialisation code
required to setup an EFI machine for booting a kernel. There's really
no need to have this code in two places and the hope is that, with
this new protocol, initialisation and booting of the kernel can be
left solely to the kernel's EFI boot stub. The responsibilities of the
boot loader then become,

   o Loading the kernel image from boot media

File system code still needs to be carried by boot loaders for the
scenario where the kernel and initrd files reside on a file system
that the EFI firmware doesn't natively understand, such as ext4, etc.

   o Providing a user interface

Boot loaders still need to display any menus/interfaces, for example
to allow the user to select from a list of kernels.

Bump the boot protocol number because we added the 'handover_offset'
field to indicate the location of the handover protocol entry point.

Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Peter Jones <pjones@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
Acked-and-Tested-by: Matthew Garrett <mjg@redhat.com>
Link: http://lkml.kernel.org/r/1342689828-16815-1-git-send-email-matt@console-pimps.org
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

Documentation/x86/boot.txt

@@ -54,6 +54,9 @@ Protocol 2.10:	(Kernel 2.6.31) Added a protocol for relaxed alignment
 		beyond the kernel_alignment added, new init_size and
 		pref_address fields.  Added extended boot loader IDs.
 
+Protocol 2.11:	(Kernel 3.6) Added a field for offset of EFI handover
+		protocol entry point.
+
 **** MEMORY LAYOUT
 
 The traditional memory map for the kernel loader, used for Image or
@@ -189,6 +192,7 @@ Offset	Proto	Name		Meaning
 				of struct setup_data
 0258/8	2.10+	pref_address	Preferred loading address
 0260/4	2.10+	init_size	Linear memory required during initialization
+0264/4	2.11+	handover_offset	Offset of handover entry point
 
 (1) For backwards compatibility, if the setup_sects field contains 0, the
     real value is 4.
@@ -690,6 +694,16 @@ Offset/size:	0x260/4
   else
 	runtime_start = pref_address
 
+Field name:	handover_offset
+Type:		read
+Offset/size:	0x264/4
+
+  This field is the offset from the beginning of the kernel image to
+  the EFI handover protocol entry point. Boot loaders using the EFI
+  handover protocol to boot the kernel should jump to this offset.
+
+  See EFI HANDOVER PROTOCOL below for more details.
+
 
 **** THE IMAGE CHECKSUM
 
@@ -1010,3 +1024,30 @@ segment; __BOOS_CS must have execute/read permission, and __BOOT_DS
 must have read/write permission; CS must be __BOOT_CS and DS, ES, SS
 must be __BOOT_DS; interrupt must be disabled; %esi must hold the base
 address of the struct boot_params; %ebp, %edi and %ebx must be zero.
+
+**** EFI HANDOVER PROTOCOL
+
+This protocol allows boot loaders to defer initialisation to the EFI
+boot stub. The boot loader is required to load the kernel/initrd(s)
+from the boot media and jump to the EFI handover protocol entry point
+which is hdr->handover_offset bytes from the beginning of
+startup_{32,64}.
+
+The function prototype for the handover entry point looks like this,
+
+    efi_main(void *handle, efi_system_table_t *table, struct boot_params *bp)
+
+'handle' is the EFI image handle passed to the boot loader by the EFI
+firmware, 'table' is the EFI system table - these are the first two
+arguments of the "handoff state" as described in section 2.3 of the
+UEFI specification. 'bp' is the boot loader-allocated boot params.
+
+The boot loader *must* fill out the following fields in bp,
+
+    o hdr.code32_start
+    o hdr.cmd_line_ptr
+    o hdr.cmdline_size
+    o hdr.ramdisk_image (if applicable)
+    o hdr.ramdisk_size  (if applicable)
+
+All other fields should be zero.

arch/x86/boot/compressed/eboot.c

@@ -729,32 +729,68 @@ static efi_status_t handle_ramdisks(efi_loaded_image_t *image,
  * need to create one ourselves (usually the bootloader would create
  * one for us).
  */
-static efi_status_t make_boot_params(struct boot_params *boot_params,
-				     efi_loaded_image_t *image,
-				     void *handle)
+struct boot_params *make_boot_params(void *handle, efi_system_table_t *_table)
 {
-	struct efi_info *efi = &boot_params->efi_info;
-	struct apm_bios_info *bi = &boot_params->apm_bios_info;
-	struct sys_desc_table *sdt = &boot_params->sys_desc_table;
-	struct e820entry *e820_map = &boot_params->e820_map[0];
-	struct e820entry *prev = NULL;
-	struct setup_header *hdr = &boot_params->hdr;
-	unsigned long size, key, desc_size, _size;
-	efi_memory_desc_t *mem_map;
-	void *options = image->load_options;
-	u32 load_options_size = image->load_options_size / 2; /* ASCII */
+	struct boot_params *boot_params;
+	struct sys_desc_table *sdt;
+	struct apm_bios_info *bi;
+	struct setup_header *hdr;
+	struct efi_info *efi;
+	efi_loaded_image_t *image;
+	void *options;
+	u32 load_options_size;
+	efi_guid_t proto = LOADED_IMAGE_PROTOCOL_GUID;
 	int options_size = 0;
 	efi_status_t status;
-	__u32 desc_version;
 	unsigned long cmdline;
-	u8 nr_entries;
 	u16 *s2;
 	u8 *s1;
 	int i;
 
+	sys_table = _table;
+
+	/* Check if we were booted by the EFI firmware */
+	if (sys_table->hdr.signature != EFI_SYSTEM_TABLE_SIGNATURE)
+		return NULL;
+
+	status = efi_call_phys3(sys_table->boottime->handle_protocol,
+				handle, &proto, (void *)&image);
+	if (status != EFI_SUCCESS) {
+		efi_printk("Failed to get handle for LOADED_IMAGE_PROTOCOL\n");
+		return NULL;
+	}
+
+	status = low_alloc(0x4000, 1, (unsigned long *)&boot_params);
+	if (status != EFI_SUCCESS) {
+		efi_printk("Failed to alloc lowmem for boot params\n");
+		return NULL;
+	}
+
+	memset(boot_params, 0x0, 0x4000);
+
+	hdr = &boot_params->hdr;
+	efi = &boot_params->efi_info;
+	bi = &boot_params->apm_bios_info;
+	sdt = &boot_params->sys_desc_table;
+
+	/* Copy the second sector to boot_params */
+	memcpy(&hdr->jump, image->image_base + 512, 512);
+
+	/*
+	 * Fill out some of the header fields ourselves because the
+	 * EFI firmware loader doesn't load the first sector.
+	 */
+	hdr->root_flags = 1;
+	hdr->vid_mode = 0xffff;
+	hdr->boot_flag = 0xAA55;
+
+	hdr->code32_start = (__u64)(unsigned long)image->image_base;
+
 	hdr->type_of_loader = 0x21;
 
 	/* Convert unicode cmdline to ascii */
+	options = image->load_options;
+	load_options_size = image->load_options_size / 2; /* ASCII */
 	cmdline = 0;
 	s2 = (u16 *)options;
 
@@ -791,18 +827,36 @@ static efi_status_t make_boot_params(struct boot_params *boot_params,
 	hdr->ramdisk_image = 0;
 	hdr->ramdisk_size = 0;
 
-	status = handle_ramdisks(image, hdr);
-	if (status != EFI_SUCCESS)
-		goto free_cmdline;
-
-	setup_graphics(boot_params);
-
 	/* Clear APM BIOS info */
 	memset(bi, 0, sizeof(*bi));
 
 	memset(sdt, 0, sizeof(*sdt));
 
-	memcpy(&efi->efi_loader_signature, EFI_LOADER_SIGNATURE, sizeof(__u32));
+	status = handle_ramdisks(image, hdr);
+	if (status != EFI_SUCCESS)
+		goto fail2;
+
+	return boot_params;
+fail2:
+	if (options_size)
+		low_free(options_size, hdr->cmd_line_ptr);
+fail:
+	low_free(0x4000, (unsigned long)boot_params);
+	return NULL;
+}
+
+static efi_status_t exit_boot(struct boot_params *boot_params,
+			      void *handle)
+{
+	struct efi_info *efi = &boot_params->efi_info;
+	struct e820entry *e820_map = &boot_params->e820_map[0];
+	struct e820entry *prev = NULL;
+	unsigned long size, key, desc_size, _size;
+	efi_memory_desc_t *mem_map;
+	efi_status_t status;
+	__u32 desc_version;
+	u8 nr_entries;
+	int i;
 
 	size = sizeof(*mem_map) * 32;
 
@@ -811,7 +865,7 @@ static efi_status_t make_boot_params(struct boot_params *boot_params,
 	_size = size;
 	status = low_alloc(size, 1, (unsigned long *)&mem_map);
 	if (status != EFI_SUCCESS)
-		goto free_cmdline;
+		return status;
 
 	status = efi_call_phys5(sys_table->boottime->get_memory_map, &size,
 				mem_map, &key, &desc_size, &desc_version);
@@ -823,6 +877,7 @@ static efi_status_t make_boot_params(struct boot_params *boot_params,
 	if (status != EFI_SUCCESS)
 		goto free_mem_map;
 
+	memcpy(&efi->efi_loader_signature, EFI_LOADER_SIGNATURE, sizeof(__u32));
 	efi->efi_systab = (unsigned long)sys_table;
 	efi->efi_memdesc_size = desc_size;
 	efi->efi_memdesc_version = desc_version;
@@ -906,61 +961,13 @@ static efi_status_t make_boot_params(struct boot_params *boot_params,
 
 free_mem_map:
 	low_free(_size, (unsigned long)mem_map);
-free_cmdline:
-	if (options_size)
-		low_free(options_size, hdr->cmd_line_ptr);
-fail:
 	return status;
 }
 
-/*
- * On success we return a pointer to a boot_params structure, and NULL
- * on failure.
- */
-struct boot_params *efi_main(void *handle, efi_system_table_t *_table)
+static efi_status_t relocate_kernel(struct setup_header *hdr)
 {
-	struct boot_params *boot_params;
 	unsigned long start, nr_pages;
-	struct desc_ptr *gdt, *idt;
-	efi_loaded_image_t *image;
-	struct setup_header *hdr;
 	efi_status_t status;
-	efi_guid_t proto = LOADED_IMAGE_PROTOCOL_GUID;
-	struct desc_struct *desc;
-
-	sys_table = _table;
-
-	/* Check if we were booted by the EFI firmware */
-	if (sys_table->hdr.signature != EFI_SYSTEM_TABLE_SIGNATURE)
-		goto fail;
-
-	status = efi_call_phys3(sys_table->boottime->handle_protocol,
-				handle, &proto, (void *)&image);
-	if (status != EFI_SUCCESS) {
-		efi_printk("Failed to get handle for LOADED_IMAGE_PROTOCOL\n");
-		goto fail;
-	}
-
-	status = low_alloc(0x4000, 1, (unsigned long *)&boot_params);
-	if (status != EFI_SUCCESS) {
-		efi_printk("Failed to alloc lowmem for boot params\n");
-		goto fail;
-	}
-
-	memset(boot_params, 0x0, 0x4000);
-
-	hdr = &boot_params->hdr;
-
-	/* Copy the second sector to boot_params */
-	memcpy(&hdr->jump, image->image_base + 512, 512);
-
-	/*
-	 * Fill out some of the header fields ourselves because the
-	 * EFI firmware loader doesn't load the first sector.
-	 */
-	hdr->root_flags = 1;
-	hdr->vid_mode = 0xffff;
-	hdr->boot_flag = 0xAA55;
 
 	/*
 	 * The EFI firmware loader could have placed the kernel image
@@ -978,16 +985,40 @@ struct boot_params *efi_main(void *handle, efi_system_table_t *_table)
 	if (status != EFI_SUCCESS) {
 		status = low_alloc(hdr->init_size, hdr->kernel_alignment,
 				   &start);
-		if (status != EFI_SUCCESS) {
+		if (status != EFI_SUCCESS)
 			efi_printk("Failed to alloc mem for kernel\n");
-			goto fail;
-		}
 	}
 
+	if (status == EFI_SUCCESS)
+		memcpy((void *)start, (void *)(unsigned long)hdr->code32_start,
+		       hdr->init_size);
+
+	hdr->pref_address = hdr->code32_start;
 	hdr->code32_start = (__u32)start;
-	hdr->pref_address = (__u64)(unsigned long)image->image_base;
 
-	memcpy((void *)start, image->image_base, image->image_size);
+	return status;
+}
+
+/*
+ * On success we return a pointer to a boot_params structure, and NULL
+ * on failure.
+ */
+struct boot_params *efi_main(void *handle, efi_system_table_t *_table,
+			     struct boot_params *boot_params)
+{
+	struct desc_ptr *gdt, *idt;
+	efi_loaded_image_t *image;
+	struct setup_header *hdr = &boot_params->hdr;
+	efi_status_t status;
+	struct desc_struct *desc;
+
+	sys_table = _table;
+
+	/* Check if we were booted by the EFI firmware */
+	if (sys_table->hdr.signature != EFI_SYSTEM_TABLE_SIGNATURE)
+		goto fail;
+
+	setup_graphics(boot_params);
 
 	status = efi_call_phys3(sys_table->boottime->allocate_pool,
 				EFI_LOADER_DATA, sizeof(*gdt),
@@ -1015,7 +1046,18 @@ struct boot_params *efi_main(void *handle, efi_system_table_t *_table)
 	idt->size = 0;
 	idt->address = 0;
 
-	status = make_boot_params(boot_params, image, handle);
+	/*
+	 * If the kernel isn't already loaded at the preferred load
+	 * address, relocate it.
+	 */
+	if (hdr->pref_address != hdr->code32_start) {
+		status = relocate_kernel(hdr);
+
+		if (status != EFI_SUCCESS)
+			goto fail;
+	}
+
+	status = exit_boot(boot_params, handle);
 	if (status != EFI_SUCCESS)
 		goto fail;
 

arch/x86/boot/compressed/head_32.S

@@ -42,6 +42,16 @@ ENTRY(startup_32)
 	 */
 	add	$0x4, %esp
 
+	call	make_boot_params
+	cmpl	$0, %eax
+	je	1f
+	movl	0x4(%esp), %esi
+	movl	(%esp), %ecx
+	pushl	%eax
+	pushl	%esi
+	pushl	%ecx
+
+	.org 0x30,0x90
 	call	efi_main
 	cmpl	$0, %eax
 	movl	%eax, %esi

arch/x86/boot/compressed/head_64.S

@@ -209,6 +209,16 @@ ENTRY(startup_64)
 	.org 0x210
 	mov	%rcx, %rdi
 	mov	%rdx, %rsi
+	pushq	%rdi
+	pushq	%rsi
+	call	make_boot_params
+	cmpq	$0,%rax
+	je	1f
+	mov	%rax, %rdx
+	popq	%rsi
+	popq	%rdi
+
+	.org 0x230,0x90
 	call	efi_main
 	movq	%rax,%rsi
 	cmpq	$0,%rax

arch/x86/boot/header.S

@@ -263,7 +263,7 @@ _start:
 	# Part 2 of the header, from the old setup.S
 
 		.ascii	"HdrS"		# header signature
-		.word	0x020a		# header version number (>= 0x0105)
+		.word	0x020b		# header version number (>= 0x0105)
 					# or else old loadlin-1.5 will fail)
 		.globl realmode_swtch
 realmode_swtch:	.word	0, 0		# default_switch, SETUPSEG
@@ -381,6 +381,8 @@ pref_address:		.quad LOAD_PHYSICAL_ADDR	# preferred load addr
 #define INIT_SIZE VO_INIT_SIZE
 #endif
 init_size:		.long INIT_SIZE		# kernel initialization size
+handover_offset:	.long 0x30		# offset to the handover
+						# protocol entry point
 
 # End of setup header #####################################################
 

arch/x86/include/asm/bootparam.h

@@ -66,6 +66,7 @@ struct setup_header {
 	__u64	setup_data;
 	__u64	pref_address;
 	__u32	init_size;
+	__u32	handover_offset;
 } __attribute__((packed));
 
 struct sys_desc_table {