/* 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/desc_defs.h>
#include <asm/msr.h>
#include <asm/page_types.h>
#include <asm/pgtable_types.h>
#include <asm/processor-flags.h>
#include <asm/segment.h>
.text
.code32
#ifdef CONFIG_EFI_HANDOVER_PROTOCOL
SYM_FUNC_START(efi32_stub_entry)
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
cld
rep stosl
add $0x4, %esp
/* Discard return address */
movl 8(%esp), %ebx
/* struct boot_params pointer */
jmp efi32_startup
SYM_FUNC_END(efi32_stub_entry)
#endif
/*
* Called using a far call from __efi64_thunk() below, using the x86_64 SysV
* ABI (except for R8/R9 which are inaccessible to 32-bit code - EAX/EBX are
* used instead). EBP+16 points to the arguments passed via the stack.
*
* The first argument (EDI) is a pointer to the boot service or protocol, to
* which the remaining arguments are passed, each truncated to 32 bits.
*/
SYM_FUNC_START_LOCAL(efi_enter32)
/*
* Convert x86-64 SysV ABI params to i386 ABI
*/
pushl 32(%ebp)
/* Up to 3 args passed via the stack */
pushl 24(%ebp)
pushl 16(%ebp)
pushl %ebx
/* R9 */
pushl %eax
/* R8 */
pushl %ecx
pushl %edx
pushl %esi
/* Disable paging */
movl %cr0, %eax
btrl $X86_CR0_PG_BIT, %eax
movl %eax, %cr0
/* Disable long mode via EFER */
movl $MSR_EFER, %ecx
rdmsr
btrl $_EFER_LME, %eax
wrmsr
call *%edi
/* We must preserve return value */
movl %eax, %edi
call efi32_enable_long_mode
addl $32, %esp
movl %edi, %eax
lret
SYM_FUNC_END(efi_enter32)
.code64
SYM_FUNC_START(__efi64_thunk)
push %rbp
movl %esp, %ebp
push %rbx
/* Move args #5 and #6 into 32-bit accessible registers */
movl %r8d, %eax
movl %r9d, %ebx
lcalll *efi32_call(%rip)
pop %rbx
pop %rbp
RET
SYM_FUNC_END(__efi64_thunk)
.code32
SYM_FUNC_START_LOCAL(efi32_enable_long_mode)
movl %cr4, %eax
btsl $(X86_CR4_PAE_BIT), %eax
movl %eax, %cr4
movl $MSR_EFER, %ecx
rdmsr
btsl $_EFER_LME, %eax
wrmsr
/* Disable interrupts - the firmware's IDT does not work in long mode */
cli
/* Enable paging */
movl %cr0, %eax
btsl $X86_CR0_PG_BIT, %eax
movl %eax, %cr0
ret
SYM_FUNC_END(efi32_enable_long_mode)
/*
* This is the common EFI stub entry point for mixed mode. It sets up the GDT
* and page tables needed for 64-bit execution, after which it calls the
* common 64-bit EFI entrypoint efi_stub_entry().
*
* Arguments: 0(%esp) image handle
* 4(%esp) EFI system table pointer
* %ebx struct boot_params pointer (or NULL)
*
* 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.]
*/
SYM_FUNC_START_LOCAL(efi32_startup)
movl %esp, %ebp
subl $8, %esp
sgdtl (%esp)
/* Save GDT descriptor to the stack */
movl 2(%esp), %esi
/* Existing GDT pointer */
movzwl (%esp), %ecx
/* Existing GDT limit */
inc %ecx
/* Existing GDT size */
andl $~7, %ecx
/* Ensure size is multiple of 8 */
subl %ecx, %esp
/* Allocate new GDT */
andl $~15, %esp
/* Realign the stack */
movl %esp, %edi
/* New GDT address */
leal 7(%ecx), %eax
/* New GDT limit */
pushw %cx
/* Push 64-bit CS (for LJMP below) */
pushl %edi
/* Push new GDT address */
pushw %ax
/* Push new GDT limit */
/* Copy GDT to the stack and add a 64-bit code segment at the end */
movl $GDT_ENTRY(DESC_CODE64, 0, 0xfffff) & 0xffffffff, (%edi,%ecx)
movl $GDT_ENTRY(DESC_CODE64, 0, 0xfffff) >> 32, 4(%edi,%ecx)
shrl $2, %ecx
cld
rep movsl
/* Copy the firmware GDT */
lgdtl (%esp)
/* Switch to the new GDT */
call 1f
1: pop %edi
/* Record mixed mode entry */
movb $0x0, (efi_is64 - 1b)(%edi)
/* Set up indirect far call to re-enter 32-bit mode */
leal (efi32_call - 1b)(%edi), %eax
addl %eax, (%eax)
movw %cs, 4(%eax)
/* Disable paging */
movl %cr0, %eax
btrl $X86_CR0_PG_BIT, %eax
movl %eax, %cr0
/* Set up 1:1 mapping */
leal (pte - 1b)(%edi), %eax
movl $_PAGE_PRESENT | _PAGE_RW | _PAGE_PSE, %ecx
leal (_PAGE_PRESENT | _PAGE_RW)(%eax), %edx
2: movl %ecx, (%eax)
addl $8, %eax
addl $PMD_SIZE, %ecx
jnc 2b
movl $PAGE_SIZE, %ecx
.irpc l, 0123
movl %edx, \l * 8(%eax)
addl %ecx, %edx
.endr
addl %ecx, %eax
movl %edx, (%eax)
movl %eax, %cr3
call efi32_enable_long_mode
/* Set up far jump to 64-bit mode (CS is already on the stack) */
leal (efi_stub_entry - 1b)(%edi), %eax
movl %eax, 2(%esp)
movl 0(%ebp), %edi
movl 4(%ebp), %esi
movl %ebx, %edx
ljmpl *2(%esp)
SYM_FUNC_END(efi32_startup)
/*
* efi_status_t efi32_pe_entry(efi_handle_t image_handle,
* efi_system_table_32_t *sys_table)
*/
SYM_FUNC_START(efi32_pe_entry)
pushl %ebx // save callee-save registers
/* Check whether the CPU supports long mode */
movl $0x80000001, %eax // assume extended info support
cpuid
btl $29, %edx // check long mode bit
jnc 1f
leal 8(%esp), %esp // preserve stack alignment
xor %ebx, %ebx // no struct boot_params pointer
jmp efi32_startup // only ESP and EBX remain live
1: movl $0x80000003, %eax // EFI_UNSUPPORTED
popl %ebx
RET
SYM_FUNC_END(efi32_pe_entry)
#ifdef CONFIG_EFI_HANDOVER_PROTOCOL
.org efi32_stub_entry + 0x200
.code64
SYM_FUNC_START_NOALIGN(efi64_stub_entry)
jmp efi_handover_entry
SYM_FUNC_END(efi64_stub_entry)
#endif
.
data
.balign 8
SYM_DATA_START_LOCAL(efi32_call)
.long efi_enter32 - .
.
word 0x0
SYM_DATA_END(efi32_call)
SYM_DATA(efi_is64, .byte 1)
.bss
.balign PAGE_SIZE
SYM_DATA_LOCAL(pte, .fill 6 * PAGE_SIZE, 1, 0)
