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/* SPDX-License-Identifier: GPL-2.0 */
/*
* Copyright (C) 2014 Intel Corporation; author Matt Fleming
*
* Support for invoking 32-bit EFI runtime services from a 64-bit
* kernel.
*
* The below thunking functions are only used after ExitBootServices()
* has been called. This simplifies things considerably as compared with
* the early EFI thunking because we can leave all the kernel state
* intact (GDT, IDT, etc) and simply invoke the 32-bit EFI runtime
* services from __KERNEL32_CS. This means we can continue to service
* interrupts across an EFI mixed mode call.
*
* We do however, need to handle the fact that we're running in a full
* 64-bit virtual address space. Things like the stack and instruction
* addresses need to be accessible by the 32-bit firmware, so we rely on
* using the identity mappings in the EFI page table to access the stack
* and kernel text (see efi_setup_page_tables()).
*/
#include <linux/linkage.h>
#include <linux/objtool.h>
#include <asm/page_types.h>
#include <asm/segment.h>
.text
.code64
SYM_FUNC_START(__efi64_thunk)
STACK_FRAME_NON_STANDARD __efi64_thunk
push %rbp
push %rbx
/*
* Switch to 1:1 mapped 32-bit stack pointer.
*/
movq %rsp, %rax
movq efi_mixed_mode_stack_pa(%rip), %rsp
push %rax
/*
* Copy args passed via the stack
*/
subq $0x24, %rsp
movq 0x18(%rax), %rbp
movq 0x20(%rax), %rbx
movq 0x28(%rax), %rax
movl %ebp, 0x18(%rsp)
movl %ebx, 0x1c(%rsp)
movl %eax, 0x20(%rsp)
/*
* Calculate the physical address of the kernel text.
*/
movq $__START_KERNEL_map, %rax
subq phys_base(%rip), %rax
leaq 1f(%rip), %rbp
leaq 2f(%rip), %rbx
subq %rax, %rbp
subq %rax, %rbx
movl %ebx, 0x0(%rsp) /* return address */
movl %esi, 0x4(%rsp)
movl %edx, 0x8(%rsp)
movl %ecx, 0xc(%rsp)
movl %r8d, 0x10(%rsp)
movl %r9d, 0x14(%rsp)
/* Switch to 32-bit descriptor */
pushq $__KERNEL32_CS
pushq %rdi /* EFI runtime service address */
lretq
// This return instruction is not needed for correctness, as it will
// never be reached. It only exists to make objtool happy, which will
// otherwise complain about unreachable instructions in the callers.
RET
SYM_FUNC_END(__efi64_thunk)
.section ".rodata", "a", @progbits
.balign 16
SYM_DATA_START(__efi64_thunk_ret_tramp)
1: movq 0x20(%rsp), %rsp
pop %rbx
pop %rbp
ret
int3
.code32
2: pushl $__KERNEL_CS
pushl %ebp
lret
SYM_DATA_END(__efi64_thunk_ret_tramp)
.bss
.balign 8
SYM_DATA(efi_mixed_mode_stack_pa, .quad 0)
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