/* 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 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 <asm/page_types.h>
#include <asm/segment.h>
.text
.code64
ENTRY(efi64_thunk)
push %rbp
push %rbx
/*
* Switch to 1:1 mapped 32-bit stack pointer.
*/
movq %rsp, efi_saved_sp(%rip)
movq efi_scratch(%rip), %rsp
/*
* Calculate the physical address of the kernel text.
*/
movq $__START_KERNEL_map, %rax
subq phys_base(%rip), %rax
/*
* Push some physical addresses onto the stack. This is easier
* to do now in a code64 section while the assembler can address
* 64-bit values. Note that all the addresses on the stack are
* 32-bit.
*/
subq $16, %rsp
leaq efi_exit32(%rip), %rbx
subq %rax, %rbx
movl %ebx, 8(%rsp)
leaq __efi64_thunk(%rip), %rbx
subq %rax, %rbx
call *%rbx
movq efi_saved_sp(%rip), %rsp
pop %rbx
pop %rbp
retq
ENDPROC(efi64_thunk)
/*
* We run this function from the 1:1 mapping.
*
* This function must be invoked with a 1:1 mapped stack.
*/
ENTRY(__efi64_thunk)
movl %ds, %eax
push %rax
movl %es, %eax
push %rax
movl %ss, %eax
push %rax
subq $32, %rsp
movl %esi, 0x0(%rsp)
movl %edx, 0x4(%rsp)
movl %ecx, 0x8(%rsp)
movq %r8, %rsi
movl %esi, 0xc(%rsp)
movq %r9, %rsi
movl %esi, 0x10(%rsp)
leaq 1f(%rip), %rbx
movq %rbx, func_rt_ptr(%rip)
/* Switch to 32-bit descriptor */
pushq $__KERNEL32_CS
leaq efi_enter32(%rip), %rax
pushq %rax
lretq
1: addq $32, %rsp
pop %rbx
movl %ebx, %ss
pop %rbx
movl %ebx, %es
pop %rbx
movl %ebx, %ds
/*
* Convert 32-bit status code into 64-bit.
*/
test %rax, %rax
jz 1f
movl %eax, %ecx
andl $0x0fffffff, %ecx
andl $0xf0000000, %eax
shl $32, %rax
or %rcx, %rax
1:
ret
ENDPROC(__efi64_thunk)
ENTRY(efi_exit32)
movq func_rt_ptr(%rip), %rax
push %rax
mov %rdi, %rax
ret
ENDPROC(efi_exit32)
.code32
/*
* EFI service pointer must be in %edi.
*
* The stack should represent the 32-bit calling convention.
*/
ENTRY(efi_enter32)
movl $__KERNEL_DS, %eax
movl %eax, %ds
movl %eax, %es
movl %eax, %ss
call *%edi
/* We must preserve return value */
movl %eax, %edi
movl 72(%esp), %eax
pushl $__KERNEL_CS
pushl %eax
lret
ENDPROC(efi_enter32)
.data
.balign 8
func_rt_ptr: .quad 0
efi_saved_sp: .quad 0
