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 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 <asm/page_types.h>
24#include <asm/segment.h>
25
26	.text
27	.code64
28ENTRY(efi64_thunk)
29	push	%rbp
30	push	%rbx
31
32	/*
33	 * Switch to 1:1 mapped 32-bit stack pointer.
34	 */
35	movq	%rsp, efi_saved_sp(%rip)
36	movq	efi_scratch(%rip), %rsp
37
38	/*
39	 * Calculate the physical address of the kernel text.
40	 */
41	movq	$__START_KERNEL_map, %rax
42	subq	phys_base(%rip), %rax
43
44	/*
45	 * Push some physical addresses onto the stack. This is easier
46	 * to do now in a code64 section while the assembler can address
47	 * 64-bit values. Note that all the addresses on the stack are
48	 * 32-bit.
49	 */
50	subq	$16, %rsp
51	leaq	efi_exit32(%rip), %rbx
52	subq	%rax, %rbx
53	movl	%ebx, 8(%rsp)
54
55	leaq	__efi64_thunk(%rip), %rbx
56	subq	%rax, %rbx
57	call	*%rbx
58
59	movq	efi_saved_sp(%rip), %rsp
60	pop	%rbx
61	pop	%rbp
62	retq
63ENDPROC(efi64_thunk)
64
65/*
66 * We run this function from the 1:1 mapping.
67 *
68 * This function must be invoked with a 1:1 mapped stack.
69 */
70ENTRY(__efi64_thunk)
71	movl	%ds, %eax
72	push	%rax
73	movl	%es, %eax
74	push	%rax
75	movl	%ss, %eax
76	push	%rax
77
78	subq	$32, %rsp
79	movl	%esi, 0x0(%rsp)
80	movl	%edx, 0x4(%rsp)
81	movl	%ecx, 0x8(%rsp)
82	movq	%r8, %rsi
83	movl	%esi, 0xc(%rsp)
84	movq	%r9, %rsi
85	movl	%esi,  0x10(%rsp)
86
87	leaq	1f(%rip), %rbx
88	movq	%rbx, func_rt_ptr(%rip)
89
90	/* Switch to 32-bit descriptor */
91	pushq	$__KERNEL32_CS
92	leaq	efi_enter32(%rip), %rax
93	pushq	%rax
94	lretq
95
961:	addq	$32, %rsp
97
98	pop	%rbx
99	movl	%ebx, %ss
100	pop	%rbx
101	movl	%ebx, %es
102	pop	%rbx
103	movl	%ebx, %ds
104
105	/*
106	 * Convert 32-bit status code into 64-bit.
107	 */
108	test	%rax, %rax
109	jz	1f
110	movl	%eax, %ecx
111	andl	$0x0fffffff, %ecx
112	andl	$0xf0000000, %eax
113	shl	$32, %rax
114	or	%rcx, %rax
1151:
116	ret
117ENDPROC(__efi64_thunk)
118
119ENTRY(efi_exit32)
120	movq	func_rt_ptr(%rip), %rax
121	push	%rax
122	mov	%rdi, %rax
123	ret
124ENDPROC(efi_exit32)
125
126	.code32
127/*
128 * EFI service pointer must be in %edi.
129 *
130 * The stack should represent the 32-bit calling convention.
131 */
132ENTRY(efi_enter32)
133	movl	$__KERNEL_DS, %eax
134	movl	%eax, %ds
135	movl	%eax, %es
136	movl	%eax, %ss
137
138	call	*%edi
139
140	/* We must preserve return value */
141	movl	%eax, %edi
142
143	movl	72(%esp), %eax
144	pushl	$__KERNEL_CS
145	pushl	%eax
146
147	lret
148ENDPROC(efi_enter32)
149
150	.data
151	.balign	8
152func_rt_ptr:		.quad 0
153efi_saved_sp:		.quad 0
154