1/* SPDX-License-Identifier: GPL-2.0 */
2/*
3 * Copyright (C) 2014 Intel Corporation; author Matt Fleming
4 *
5 * Support for invoking 32-bit EFI runtime services from a 64-bit
6 * kernel.
7 *
8 * The below thunking functions are only used after ExitBootServices()
9 * has been called. This simplifies things considerably as compared with
10 * the early EFI thunking because we can leave all the kernel state
11 * intact (GDT, IDT, etc) and simply invoke the 32-bit EFI runtime
12 * services from __KERNEL32_CS. This means we can continue to service
13 * interrupts across an EFI mixed mode call.
14 *
15 * We do however, need to handle the fact that we're running in a full
16 * 64-bit virtual address space. Things like the stack and instruction
17 * addresses need to be accessible by the 32-bit firmware, so we rely on
18 * using the identity mappings in the EFI page table to access the stack
19 * and kernel text (see efi_setup_page_tables()).
20 */
21
22#include <linux/linkage.h>
23#include <linux/objtool.h>
24#include <asm/page_types.h>
25#include <asm/segment.h>
26
27	.text
28	.code64
29SYM_FUNC_START(__efi64_thunk)
30STACK_FRAME_NON_STANDARD __efi64_thunk
31	push	%rbp
32	push	%rbx
33
34	/*
35	 * Switch to 1:1 mapped 32-bit stack pointer.
36	 */
37	movq	%rsp, %rax
38	movq	efi_mixed_mode_stack_pa(%rip), %rsp
39	push	%rax
40
41	/*
42	 * Copy args passed via the stack
43	 */
44	subq	$0x24, %rsp
45	movq	0x18(%rax), %rbp
46	movq	0x20(%rax), %rbx
47	movq	0x28(%rax), %rax
48	movl	%ebp, 0x18(%rsp)
49	movl	%ebx, 0x1c(%rsp)
50	movl	%eax, 0x20(%rsp)
51
52	/*
53	 * Calculate the physical address of the kernel text.
54	 */
55	movq	$__START_KERNEL_map, %rax
56	subq	phys_base(%rip), %rax
57
58	leaq	1f(%rip), %rbp
59	leaq	2f(%rip), %rbx
60	subq	%rax, %rbp
61	subq	%rax, %rbx
62
63	movl	%ebx, 0x0(%rsp)		/* return address */
64	movl	%esi, 0x4(%rsp)
65	movl	%edx, 0x8(%rsp)
66	movl	%ecx, 0xc(%rsp)
67	movl	%r8d, 0x10(%rsp)
68	movl	%r9d, 0x14(%rsp)
69
70	/* Switch to 32-bit descriptor */
71	pushq	$__KERNEL32_CS
72	pushq	%rdi			/* EFI runtime service address */
73	lretq
74
75	// This return instruction is not needed for correctness, as it will
76	// never be reached. It only exists to make objtool happy, which will
77	// otherwise complain about unreachable instructions in the callers.
78	RET
79SYM_FUNC_END(__efi64_thunk)
80
81	.section ".rodata", "a", @progbits
82	.balign	16
83SYM_DATA_START(__efi64_thunk_ret_tramp)
841:	movq	0x20(%rsp), %rsp
85	pop	%rbx
86	pop	%rbp
87	ret
88	int3
89
90	.code32
912:	pushl	$__KERNEL_CS
92	pushl	%ebp
93	lret
94SYM_DATA_END(__efi64_thunk_ret_tramp)
95
96	.bss
97	.balign 8
98SYM_DATA(efi_mixed_mode_stack_pa, .quad 0)
99