blob: 719e939050cbfa0b9d574b326d46c4791a0a3eed [file] [log] [blame]
/* SPDX-License-Identifier: GPL-2.0 */
* Copyright (C) 2014, 2015 Intel Corporation; author Matt Fleming
* Early support for invoking 32-bit EFI services from a 64-bit kernel.
* Because this thunking occurs before ExitBootServices() we have to
* restore the firmware's 32-bit GDT and IDT before we make EFI service
* calls.
* On the plus side, we don't have to worry about mangling 64-bit
* addresses into 32-bits because we're executing with an identity
* mapped pagetable and haven't transitioned to 64-bit virtual addresses
* yet.
#include <linux/linkage.h>
#include <asm/msr.h>
#include <asm/page_types.h>
#include <asm/processor-flags.h>
#include <asm/segment.h>
* When booting in 64-bit mode on 32-bit EFI firmware, startup_64_mixed_mode()
* is the first thing that runs after switching to long mode. Depending on
* whether the EFI handover protocol or the compat entry point was used to
* enter the kernel, it will either branch to the common 64-bit EFI stub
* entrypoint efi_stub_entry() directly, or via the 64-bit EFI PE/COFF
* entrypoint efi_pe_entry(). In the former case, the bootloader must provide a
* struct bootparams pointer as the third argument, so the presence of such a
* pointer is used to disambiguate.
* +--------------+
* +------------------+ +------------+ +------>| efi_pe_entry |
* | efi32_pe_entry |---->| | | +-----------+--+
* +------------------+ | | +------+----------------+ |
* | startup_32 |---->| startup_64_mixed_mode | |
* +------------------+ | | +------+----------------+ |
* | efi32_stub_entry |---->| | | |
* +------------------+ +------------+ | |
* V |
* +------------+ +----------------+ |
* | startup_64 |<----| efi_stub_entry |<--------+
* +------------+ +----------------+
lea efi32_boot_args(%rip), %rdx
mov 0(%rdx), %edi
mov 4(%rdx), %esi
/* Switch to the firmware's stack */
movl efi32_boot_sp(%rip), %esp
andl $~7, %esp
mov 8(%rdx), %edx // saved bootparams pointer
test %edx, %edx
jnz efi_stub_entry
* efi_pe_entry uses MS calling convention, which requires 32 bytes of
* shadow space on the stack even if all arguments are passed in
* registers. We also need an additional 8 bytes for the space that
* would be occupied by the return address, and this also results in
* the correct stack alignment for entry.
sub $40, %rsp
mov %rdi, %rcx // MS calling convention
mov %rsi, %rdx
jmp efi_pe_entry
push %rbp
push %rbx
movl %ds, %eax
push %rax
movl %es, %eax
push %rax
movl %ss, %eax
push %rax
/* Copy args passed on stack */
movq 0x30(%rsp), %rbp
movq 0x38(%rsp), %rbx
movq 0x40(%rsp), %rax
* Convert x86-64 ABI params to i386 ABI
subq $64, %rsp
movl %esi, 0x0(%rsp)
movl %edx, 0x4(%rsp)
movl %ecx, 0x8(%rsp)
movl %r8d, 0xc(%rsp)
movl %r9d, 0x10(%rsp)
movl %ebp, 0x14(%rsp)
movl %ebx, 0x18(%rsp)
movl %eax, 0x1c(%rsp)
leaq 0x20(%rsp), %rbx
sgdt (%rbx)
sidt 16(%rbx)
leaq 1f(%rip), %rbp
* Switch to IDT and GDT with 32-bit segments. These are the firmware
* GDT and IDT that were installed when the kernel started executing.
* The pointers were saved by the efi32_entry() routine below.
* Pass the saved DS selector to the 32-bit code, and use far return to
* restore the saved CS selector.
lidt efi32_boot_idt(%rip)
lgdt efi32_boot_gdt(%rip)
movzwl efi32_boot_ds(%rip), %edx
movzwq efi32_boot_cs(%rip), %rax
pushq %rax
leaq efi_enter32(%rip), %rax
pushq %rax
1: addq $64, %rsp
movq %rdi, %rax
pop %rbx
movl %ebx, %ss
pop %rbx
movl %ebx, %es
pop %rbx
movl %ebx, %ds
/* Clear out 32-bit selector from FS and GS */
xorl %ebx, %ebx
movl %ebx, %fs
movl %ebx, %gs
pop %rbx
pop %rbp
call 1f
1: popl %ecx
/* Clear BSS */
xorl %eax, %eax
leal (_bss - 1b)(%ecx), %edi
leal (_ebss - 1b)(%ecx), %ecx
subl %edi, %ecx
shrl $2, %ecx
rep stosl
add $0x4, %esp /* Discard return address */
popl %ecx
popl %edx
popl %esi
jmp efi32_entry
* EFI service pointer must be in %edi.
* The stack should represent the 32-bit calling convention.
/* Load firmware selector into data and stack segment registers */
movl %edx, %ds
movl %edx, %es
movl %edx, %fs
movl %edx, %gs
movl %edx, %ss
/* Reload pgtables */
movl %cr3, %eax
movl %eax, %cr3
/* Disable paging */
movl %cr0, %eax
btrl $X86_CR0_PG_BIT, %eax
movl %eax, %cr0
/* Disable long mode via EFER */
movl $MSR_EFER, %ecx
btrl $_EFER_LME, %eax
call *%edi
/* We must preserve return value */
movl %eax, %edi
* Some firmware will return with interrupts enabled. Be sure to
* disable them before we switch GDTs and IDTs.
lidtl 16(%ebx)
lgdtl (%ebx)
movl %cr4, %eax
btsl $(X86_CR4_PAE_BIT), %eax
movl %eax, %cr4
movl %cr3, %eax
movl %eax, %cr3
movl $MSR_EFER, %ecx
btsl $_EFER_LME, %eax
xorl %eax, %eax
lldt %ax
pushl $__KERNEL_CS
pushl %ebp
/* Enable paging */
movl %cr0, %eax
btsl $X86_CR0_PG_BIT, %eax
movl %eax, %cr0
* This is the common EFI stub entry point for mixed mode.
* Arguments: %ecx image handle
* %edx EFI system table pointer
* %esi struct bootparams pointer (or NULL when not using
* the EFI handover protocol)
* Since this is the point of no return for ordinary execution, no registers
* are considered live except for the function parameters. [Note that the EFI
* stub may still exit and return to the firmware using the Exit() EFI boot
* service.]
call 1f
1: pop %ebx
/* Save firmware GDTR and code/data selectors */
sgdtl (efi32_boot_gdt - 1b)(%ebx)
movw %cs, (efi32_boot_cs - 1b)(%ebx)
movw %ds, (efi32_boot_ds - 1b)(%ebx)
/* Store firmware IDT descriptor */
sidtl (efi32_boot_idt - 1b)(%ebx)
/* Store firmware stack pointer */
movl %esp, (efi32_boot_sp - 1b)(%ebx)
/* Store boot arguments */
leal (efi32_boot_args - 1b)(%ebx), %ebx
movl %ecx, 0(%ebx)
movl %edx, 4(%ebx)
movl %esi, 8(%ebx)
movb $0x0, 12(%ebx) // efi_is64
/* Disable paging */
movl %cr0, %eax
btrl $X86_CR0_PG_BIT, %eax
movl %eax, %cr0
jmp startup_32
* efi_status_t efi32_pe_entry(efi_handle_t image_handle,
* efi_system_table_32_t *sys_table)
pushl %ebp
movl %esp, %ebp
pushl %ebx // save callee-save registers
pushl %edi
call verify_cpu // check for long mode support
testl %eax, %eax
movl $0x80000003, %eax // EFI_UNSUPPORTED
jnz 2f
movl 8(%ebp), %ecx // image_handle
movl 12(%ebp), %edx // sys_table
xorl %esi, %esi
jmp efi32_entry // pass %ecx, %edx, %esi
// no other registers remain live
2: popl %edi // restore callee-save registers
popl %ebx
.org efi32_stub_entry + 0x200
jmp efi_handover_entry
.balign 8
.word 0
.quad 0
.word 0
.quad 0
SYM_DATA_LOCAL(efi32_boot_cs, .word 0)
SYM_DATA_LOCAL(efi32_boot_ds, .word 0)
SYM_DATA_LOCAL(efi32_boot_sp, .long 0)
SYM_DATA_LOCAL(efi32_boot_args, .long 0, 0, 0)
SYM_DATA(efi_is64, .byte 1)