diff options
Diffstat (limited to 'arch/x86/platform/efi/efi_thunk_64.S')
| -rw-r--r-- | arch/x86/platform/efi/efi_thunk_64.S | 98 |
1 files changed, 98 insertions, 0 deletions
diff --git a/arch/x86/platform/efi/efi_thunk_64.S b/arch/x86/platform/efi/efi_thunk_64.S new file mode 100644 index 000000000..c4b1144f9 --- /dev/null +++ b/arch/x86/platform/efi/efi_thunk_64.S @@ -0,0 +1,98 @@ +/* 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) |