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 29 SYM_FUNC_START(__efi64_thunk) 30 STACK_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 79 SYM_FUNC_END(__efi64_thunk) 80 81 .section ".rodata", "a", @progbits 82 .balign 16 83 SYM_DATA_START(__efi64_thunk_ret_tramp) 84 1: movq 0x20(%rsp), %rsp 85 pop %rbx 86 pop %rbp 87 ret 88 int3 89 90 .code32 91 2: pushl $__KERNEL_CS 92 pushl %ebp 93 lret 94 SYM_DATA_END(__efi64_thunk_ret_tramp) 95 96 .bss 97 .balign 8 98 SYM_DATA(efi_mixed_mode_stack_pa, .quad 0)
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