/* SPDX-License-Identifier: GPL-2.0 */
/*
* linux/boot/head.S
*
* Copyright (C) 1991, 1992, 1993 Linus Torvalds
*/
/*
* head.S contains the 32-bit startup code.
*
* NOTE!!! Startup happens at absolute address 0x00001000, which is also where
* the page directory will exist. The startup code will be overwritten by
* the page directory. [According to comments etc elsewhere on a compressed
* kernel it will end up at 0x1000 + 1Mb I hope so as I assume this. - AC]
*
* Page 0 is deliberately kept safe, since System Management Mode code in
* laptops may need to access the BIOS data stored there. This is also
* useful for future device drivers that either access the BIOS via VM86
* mode.
*/
/*
* High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996
*/
.code32
.text
#include <linux/init.h>
#include <linux/linkage.h>
#include <asm/segment.h>
#include <asm/boot.h>
#include <asm/msr.h>
#include <asm/processor-flags.h>
#include <asm/asm-offsets.h>
#include <asm/bootparam.h>
#include <asm/desc_defs.h>
#include <asm/trapnr.h>
#include "pgtable.h"
/*
* Locally defined symbols should be marked hidden:
*/
.hidden _bss
.hidden _ebss
.hidden _end
__HEAD
/*
* This macro gives the relative virtual address of X, i.e. the offset of X
* from startup_32. This is the same as the link-time virtual address of X,
* since startup_32 is at 0, but defining it this way tells the
* assembler/linker that we do not want the actual run-time address of X. This
* prevents the linker from trying to create unwanted run-time relocation
* entries for the reference when the compressed kernel is linked as PIE.
*
* A reference X(%reg) will result in the link-time VA of X being stored with
* the instruction, and a run-time R_X86_64_RELATIVE relocation entry that
* adds the 64-bit base address where the kernel is loaded.
*
* Replacing it with (X-startup_32)(%reg) results in the offset being stored,
* and no run-time relocation.
*
* The macro should be used as a displacement with a base register containing
* the run-time address of startup_32 [i.e. rva(X)(%reg)], or as an immediate
* [$ rva(X)].
*
* This macro can only be used from within the .head.text section, since the
* expression requires startup_32 to be in the same section as the code being
* assembled.
*/
#define rva(X) ((X) - startup_32)
.code32
SYM_FUNC_START(startup_32)
/*
* 32bit entry is 0 and it is ABI so immutable!
* If we come here directly from a bootloader,
* kernel(text+data+bss+brk) ramdisk, zero_page, command line
* all need to be under the 4G limit.
*/
cld
cli
/*
* Calculate the delta between where we were compiled to run
* at and where we were actually loaded at. This can only be done
* with a short local call on x86. Nothing else will tell us what
* address we are running at. The reserved chunk of the real-mode
* data at 0x1e4 (defined as a scratch field) are used as the stack
* for this calculation. Only 4 bytes are needed.
*/
leal (BP_scratch+4)(%esi), %esp
call 1f
1: popl %ebp
subl $ rva(1b), %ebp
/* Load new GDT with the 64bit segments using 32bit descriptor */
leal rva(gdt)(%ebp), %eax
movl %eax, 2(%eax)
lgdt (%eax)
/* Load segment registers with our descriptors */
movl $__BOOT_DS, %eax
movl %eax, %ds
movl %eax, %es
movl %eax, %fs
movl %eax, %gs
movl %eax, %ss
/* Setup a stack and load CS from current GDT */
leal rva(boot_stack_end)(%ebp), %esp
pushl $__KERNEL32_CS
leal rva(1f)(%ebp), %eax
pushl %eax
lretl
1:
/* Setup Exception handling for SEV-ES */
#ifdef CONFIG_AMD_MEM_ENCRYPT
call startup32_load_idt
#endif
/* Make sure cpu supports long mode. */
call verify_cpu
testl %eax, %eax
jnz .Lno_longmode
/*
* Compute the delta between where we were compiled to run at
* and where the code will actually run at.
*
* %ebp contains the address we are loaded at by the boot loader and %ebx
* contains the address where we should move the kernel image temporarily
* for safe in-place decompression.
*/
#ifdef CONFIG_RELOCATABLE
movl %ebp, %ebx
#ifdef CONFIG_EFI_STUB
/*
* If we were loaded via the EFI LoadImage service, startup_32 will be at an
* offset to the start of the space allocated for the image. efi_pe_entry will
* set up image_offset to tell us where the image actually starts, so that we
* can use the full available buffer.
* image_offset = startup_32 - image_base
* Otherwise image_offset will be zero and has no effect on the calculations.
*/
subl rva(image_offset)(%ebp), %ebx
#endif
movl BP_kernel_alignment(%esi), %eax
decl %eax
addl %eax, %ebx
notl %eax
andl %eax, %ebx
cmpl $LOAD_PHYSICAL_ADDR, %ebx
jae 1f
#endif
movl $LOAD_PHYSICAL_ADDR, %ebx
1:
/* Target address to relocate to for decompression */
addl BP_init_size(%esi), %ebx
subl $ rva(_end), %ebx
/*
* Prepare for entering 64 bit mode
*/
/* Enable PAE mode */
movl %cr4, %eax
orl $X86_CR4_PAE, %eax
movl %eax, %cr4
/*
* Build early 4G boot pagetable
*/
/*
* If SEV is active then set the encryption mask in the page tables.
* This will ensure that when the kernel is copied and decompressed
* it will be done so encrypted.
*/
xorl %edx, %edx
#ifdef CONFIG_AMD_MEM_ENCRYPT
call get_sev_encryption_bit
xorl %edx, %edx
testl %eax, %eax
jz 1f
subl $32, %eax /* Encryption bit is always above bit 31 */
bts %eax, %edx /* Set encryption mask for page tables */
/*
* Set MSR_AMD64_SEV_ENABLED_BIT in sev_status so that
* startup32_check_sev_cbit() will do a check. sev_enable() will
* initialize sev_status with all the bits reported by
* MSR_AMD_SEV_STATUS later, but only MSR_AMD64_SEV_ENABLED_BIT
* needs to be set for now.
*/
movl $1, rva(sev_status)(%ebp)
1:
#endif
/* Initialize Page tables to 0 */
leal rva(pgtable)(%ebx), %edi
xorl %eax, %eax
movl $(BOOT_INIT_PGT_SIZE/4), %ecx
rep stosl
/* Build Level 4 */
leal rva(pgtable + 0)(%ebx), %edi
leal 0x1007 (%edi), %eax
movl %eax, 0(%edi)
addl %edx, 4(%edi)
/* Build Level 3 */
leal rva(pgtable + 0x1000)(%ebx), %edi
leal 0x1007(%edi), %eax
movl $4, %ecx
1: movl %eax, 0x00(%edi)
addl %edx, 0x04(%edi)
addl $0x00001000, %eax
addl $8, %edi
decl %ecx
jnz 1b
/* Build Level 2 */
leal rva(pgtable + 0x2000)(%ebx), %edi
movl $0x00000183, %eax
movl $2048, %ecx
1: movl %eax, 0(%edi)
addl %edx, 4(%edi)
addl $0x00200000, %eax
addl $8, %edi
decl %ecx
jnz 1b
/* Enable the boot page tables */
leal rva(pgtable)(%ebx), %eax
movl %eax, %cr3
/* Enable Long mode in EFER (Extended Feature Enable Register) */
movl $MSR_EFER, %ecx
rdmsr
btsl $_EFER_LME, %eax
wrmsr
/* After gdt is loaded */
xorl %eax, %eax
lldt %ax
movl $__BOOT_TSS, %eax
ltr %ax
#ifdef CONFIG_AMD_MEM_ENCRYPT
/* Check if the C-bit position is correct when SEV is active */
call startup32_check_sev_cbit
#endif
/*
* Setup for the jump to 64bit mode
*
* When the jump is performed we will be in long mode but
* in 32bit compatibility mode with EFER.LME = 1, CS.L = 0, CS.D = 1
* (and in turn EFER.LMA = 1). To jump into 64bit mode we use
* the new gdt/idt that has __KERNEL_CS with CS.L = 1.
* We place all of the values on our mini stack so lret can
* used to perform that far jump.
*/
leal rva(startup_64)(%ebp), %eax
#ifdef CONFIG_EFI_MIXED
cmpb $1, rva(efi_is64)(%ebp)
je 1f
leal rva(startup_64_mixed_mode)(%ebp), %eax
1:
#endif
pushl $__KERNEL_CS
pushl %eax
/* Enter paged protected Mode, activating Long Mode */
movl $CR0_STATE, %eax
movl %eax, %cr0
/* Jump from 32bit compatibility mode into 64bit mode. */
lret
SYM_FUNC_END(startup_32)
#if IS_ENABLED(CONFIG_EFI_MIXED) && IS_ENABLED(CONFIG_EFI_HANDOVER_PROTOCOL)
.org 0x190
SYM_FUNC_START(efi32_stub_entry)
add $0x4, %esp /* Discard return address */
popl %ecx
popl %edx
popl %esi
jmp efi32_entry
SYM_FUNC_END(efi32_stub_entry)
#endif
.code64
.org 0x200
SYM_CODE_START(startup_64)
/*
* 64bit entry is 0x200 and it is ABI so immutable!
* We come here either from startup_32 or directly from a
* 64bit bootloader.
* If we come here from a bootloader, kernel(text+data+bss+brk),
* ramdisk, zero_page, command line could be above 4G.
* We depend on an identity mapped page table being provided
* that maps our entire kernel(text+data+bss+brk), zero page
* and command line.
*/
cld
cli
/* Setup data segments. */
xorl %eax, %eax
movl %eax, %ds
movl %eax, %es
movl %eax, %ss
movl %eax, %fs
movl %eax, %gs
/*
* Compute the decompressed kernel start address. It is where
* we were loaded at aligned to a 2M boundary. %rbp contains the
* decompressed kernel start address.
*
* If it is a relocatable kernel then decompress and run the kernel
* from load address aligned to 2MB addr, otherwise decompress and
* run the kernel from LOAD_PHYSICAL_ADDR
*
* We cannot rely on the calculation done in 32-bit mode, since we
* may have been invoked via the 64-bit entry point.
*/
/* Start with the delta to where the kernel will run at. */
#ifdef CONFIG_RELOCATABLE
leaq startup_32(%rip) /* - $startup_32 */, %rbp
#ifdef CONFIG_EFI_STUB
/*
* If we were loaded via the EFI LoadImage service, startup_32 will be at an
* offset to the start of the space allocated for the image. efi_pe_entry will
* set up image_offset to tell us where the image actually starts, so that we
* can use the full available buffer.
* image_offset = startup_32 - image_base
* Otherwise image_offset will be zero and has no effect on the calculations.
*/
movl image_offset(%rip), %eax
subq %rax, %rbp
#endif
movl BP_kernel_alignment(%rsi), %eax
decl %eax
addq %rax, %rbp
notq %rax
andq %rax, %rbp
cmpq $LOAD_PHYSICAL_ADDR, %rbp
jae 1f
#endif
movq $LOAD_PHYSICAL_ADDR, %rbp
1:
/* Target address to relocate to for decompression */
movl BP_init_size(%rsi), %ebx
subl $ rva(_end), %ebx
addq %rbp, %rbx
/* Set up the stack */
leaq rva(boot_stack_end)(%rbx), %rsp
/*
* At this point we are in long mode with 4-level paging enabled,
* but we might want to enable 5-level paging or vice versa.
*
* The problem is that we cannot do it directly. Setting or clearing
* CR4.LA57 in long mode would trigger #GP. So we need to switch off
* long mode and paging first.
*
* We also need a trampoline in lower memory to switch over from
* 4- to 5-level paging for cases when the bootloader puts the kernel
* above 4G, but didn't enable 5-level paging for us.
*
* The same trampoline can be used to switch from 5- to 4-level paging
* mode, like when starting 4-level paging kernel via kexec() when
* original kernel worked in 5-level paging mode.
*
* For the trampoline, we need the top page table to reside in lower
* memory as we don't have a way to load 64-bit values into CR3 in
* 32-bit mode.
*
* We go though the trampoline even if we don't have to: if we're
* already in a desired paging mode. This way the trampoline code gets
* tested on every boot.
*/
/* Make sure we have GDT with 32-bit code segment */
leaq gdt64(%rip), %rax
addq %rax, 2(%rax)
lgdt (%rax)
/* Reload CS so IRET returns to a CS actually in the GDT */
pushq $__KERNEL_CS
leaq .Lon_kernel_cs(%rip), %rax
pushq %rax
lretq
.Lon_kernel_cs:
pushq %rsi
call load_stage1_idt
popq %rsi
#ifdef CONFIG_AMD_MEM_ENCRYPT
/*
* Now that the stage1 interrupt handlers are set up, #VC exceptions from
* CPUID instructions can be properly handled for SEV-ES guests.
*
* For SEV-SNP, the CPUID table also needs to be set up in advance of any
* CPUID instructions being issued, so go ahead and do that now via
* sev_enable(), which will also handle the rest of the SEV-related
* detection/setup to ensure that has been done in advance of any dependent
* code.
*/
pushq %rsi
movq %rsi, %rdi /* real mode address */
call sev_enable
popq %rsi
#endif
/*
* paging_prepare() sets up the trampoline and checks if we need to
* enable 5-level paging.
*
* paging_prepare() returns a two-quadword structure which lands
* into RDX:RAX:
* - Address of the trampoline is returned in RAX.
* - Non zero RDX means trampoline needs to enable 5-level
* paging.
*
* RSI holds real mode data and needs to be preserved across
* this function call.
*/
pushq %rsi
movq %rsi, %rdi /* real mode address */
call paging_prepare
popq %rsi
/* Save the trampoline address in RCX */
movq %rax, %rcx
/*
* Load the address of trampoline_return() into RDI.
* It will be used by the trampoline to return to the main code.
*/
leaq trampoline_return(%rip), %rdi
/* Switch to compatibility mode (CS.L = 0 CS.D = 1) via far return */
pushq $__KERNEL32_CS
leaq TRAMPOLINE_32BIT_CODE_OFFSET(%rax), %rax
pushq %rax
lretq
trampoline_return:
/* Restore the stack, the 32-bit trampoline uses its own stack */
leaq rva(boot_stack_end)(%rbx), %rsp
/*
* cleanup_trampoline() would restore trampoline memory.
*
* RDI is address of the page table to use instead of page table
* in trampoline memory (if required).
*
* RSI holds real mode data and needs to be preserved across
* this function call.
*/
pushq %rsi
leaq rva(top_pgtable)(%rbx), %rdi
call cleanup_trampoline
popq %rsi
/* Zero EFLAGS */
pushq $0
popfq
/*
* Copy the compressed kernel to the end of our buffer
* where decompression in place becomes safe.
*/
pushq %rsi
leaq (_bss-8)(%rip), %rsi
leaq rva(_bss-8)(%rbx), %rdi
movl $(_bss - startup_32), %ecx
shrl $3, %ecx
std
rep movsq
cld
popq %rsi
/*
* The GDT may get overwritten either during the copy we just did or
* during extract_kernel below. To avoid any issues, repoint the GDTR
* to the new copy of the GDT.
*/
leaq rva(gdt64)(%rbx), %rax
leaq rva(gdt)(%rbx), %rdx
movq %rdx, 2(%rax)
lgdt (%rax)
/*
* Jump to the relocated address.
*/
leaq rva(.Lrelocated)(%rbx), %rax
jmp *%rax
SYM_CODE_END(startup_64)
#ifdef CONFIG_EFI_STUB
#ifdef CONFIG_EFI_HANDOVER_PROTOCOL
.org 0x390
#endif
SYM_FUNC_START(efi64_stub_entry)
and $~0xf, %rsp /* realign the stack */
movq %rdx, %rbx /* save boot_params pointer */
call efi_main
movq %rbx,%rsi
leaq rva(startup_64)(%rax), %rax
jmp *%rax
SYM_FUNC_END(efi64_stub_entry)
SYM_FUNC_ALIAS(efi_stub_entry, efi64_stub_entry)
#endif
.text
SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
/*
* Clear BSS (stack is currently empty)
*/
xorl %eax, %eax
leaq _bss(%rip), %rdi
leaq _ebss(%rip), %rcx
subq %rdi, %rcx
shrq $3, %rcx
rep stosq
pushq %rsi
call load_stage2_idt
/* Pass boot_params to initialize_identity_maps() */
movq (%rsp), %rdi
call initialize_identity_maps
popq %rsi
/*
* Do the extraction, and jump to the new kernel..
*/
pushq %rsi /* Save the real mode argument */
movq %rsi, %rdi /* real mode address */
leaq boot_heap(%rip), %rsi /* malloc area for uncompression */
leaq input_data(%rip), %rdx /* input_data */
movl input_len(%rip), %ecx /* input_len */
movq %rbp, %r8 /* output target address */
movl output_len(%rip), %r9d /* decompressed length, end of relocs */
call extract_kernel /* returns kernel location in %rax */
popq %rsi
/*
* Jump to the decompressed kernel.
*/
jmp *%rax
SYM_FUNC_END(.Lrelocated)
.code32
/*
* This is the 32-bit trampoline that will be copied over to low memory.
*
* RDI contains the return address (might be above 4G).
* ECX contains the base address of the trampoline memory.
* Non zero RDX means trampoline needs to enable 5-level paging.
*/
SYM_CODE_START(trampoline_32bit_src)
/* Set up data and stack segments */
movl $__KERNEL_DS, %eax
movl %eax, %ds
movl %eax, %ss
/* Set up new stack */
leal TRAMPOLINE_32BIT_STACK_END(%ecx), %esp
/* Disable paging */
movl %cr0, %eax
btrl $X86_CR0_PG_BIT, %eax
movl %eax, %cr0
/* Check what paging mode we want to be in after the trampoline */
testl %edx, %edx
jz 1f
/* We want 5-level paging: don't touch CR3 if it already points to 5-level page tables */
movl %cr4, %eax
testl $X86_CR4_LA57, %eax
jnz 3f
jmp 2f
1:
/* We want 4-level paging: don't touch CR3 if it already points to 4-level page tables */
movl %cr4, %eax
testl $X86_CR4_LA57, %eax
jz 3f
2:
/* Point CR3 to the trampoline's new top level page table */
leal TRAMPOLINE_32BIT_PGTABLE_OFFSET(%ecx), %eax
movl %eax, %cr3
3:
/* Set EFER.LME=1 as a precaution in case hypervsior pulls the rug */
pushl %ecx
pushl %edx
movl $MSR_EFER, %ecx
rdmsr
btsl $_EFER_LME, %eax
/* Avoid writing EFER if no change was made (for TDX guest) */
jc 1f
wrmsr
1: popl %edx
popl %ecx
#ifdef CONFIG_X86_MCE
/*
* Preserve CR4.MCE if the kernel will enable #MC support.
* Clearing MCE may fault in some environments (that also force #MC
* support). Any machine check that occurs before #MC support is fully
* configured will crash the system regardless of the CR4.MCE value set
* here.
*/
movl %cr4, %eax
andl $X86_CR4_MCE, %eax
#else
movl $0, %eax
#endif
/* Enable PAE and LA57 (if required) paging modes */
orl $X86_CR4_PAE, %eax
testl %edx, %edx
jz 1f
orl $X86_CR4_LA57, %eax
1:
movl %eax, %cr4
/* Calculate address of paging_enabled() once we are executing in the trampoline */
leal .Lpaging_enabled - trampoline_32bit_src + TRAMPOLINE_32BIT_CODE_OFFSET(%ecx), %eax
/* Prepare the stack for far return to Long Mode */
pushl $__KERNEL_CS
pushl %eax
/* Enable paging again. */
movl %cr0, %eax
btsl $X86_CR0_PG_BIT, %eax
movl %eax, %cr0
lret
SYM_CODE_END(trampoline_32bit_src)
.code64
SYM_FUNC_START_LOCAL_NOALIGN(.Lpaging_enabled)
/* Return from the trampoline */
jmp *%rdi
SYM_FUNC_END(.Lpaging_enabled)
/*
* The trampoline code has a size limit.
* Make sure we fail to compile if the trampoline code grows
* beyond TRAMPOLINE_32BIT_CODE_SIZE bytes.
*/
.org trampoline_32bit_src + TRAMPOLINE_32BIT_CODE_SIZE
.code32
SYM_FUNC_START_LOCAL_NOALIGN(.Lno_longmode)
/* This isn't an x86-64 CPU, so hang intentionally, we cannot continue */
1:
hlt
jmp 1b
SYM_FUNC_END(.Lno_longmode)
.globl verify_cpu
#include "../../kernel/verify_cpu.S"
.data
SYM_DATA_START_LOCAL(gdt64)
.word gdt_end - gdt - 1
.quad gdt - gdt64
SYM_DATA_END(gdt64)
.balign 8
SYM_DATA_START_LOCAL(gdt)
.word gdt_end - gdt - 1
.long 0
.word 0
.quad 0x00cf9a000000ffff /* __KERNEL32_CS */
.quad 0x00af9a000000ffff /* __KERNEL_CS */
.quad 0x00cf92000000ffff /* __KERNEL_DS */
.quad 0x0080890000000000 /* TS descriptor */
.quad 0x0000000000000000 /* TS continued */
SYM_DATA_END_LABEL(gdt, SYM_L_LOCAL, gdt_end)
SYM_DATA_START(boot_idt_desc)
.word boot_idt_end - boot_idt - 1
.quad 0
SYM_DATA_END(boot_idt_desc)
.balign 8
SYM_DATA_START(boot_idt)
.rept BOOT_IDT_ENTRIES
.quad 0
.quad 0
.endr
SYM_DATA_END_LABEL(boot_idt, SYM_L_GLOBAL, boot_idt_end)
/*
* Stack and heap for uncompression
*/
.bss
.balign 4
SYM_DATA_LOCAL(boot_heap, .fill BOOT_HEAP_SIZE, 1, 0)
SYM_DATA_START_LOCAL(boot_stack)
.fill BOOT_STACK_SIZE, 1, 0
.balign 16
SYM_DATA_END_LABEL(boot_stack, SYM_L_LOCAL, boot_stack_end)
/*
* Space for page tables (not in .bss so not zeroed)
*/
.section ".pgtable","aw",@nobits
.balign 4096
SYM_DATA_LOCAL(pgtable, .fill BOOT_PGT_SIZE, 1, 0)
/*
* The page table is going to be used instead of page table in the trampoline
* memory.
*/
SYM_DATA_LOCAL(top_pgtable, .fill PAGE_SIZE, 1, 0)