/* 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 #include #include #include #include #include #include #include #include "pgtable.h" /* * Locally defined symbols should be marked hidden: */ .hidden _bss .hidden _ebss .hidden _got .hidden _egot __HEAD .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 /* * Test KEEP_SEGMENTS flag to see if the bootloader is asking * us to not reload segments */ testb $KEEP_SEGMENTS, BP_loadflags(%esi) jnz 1f cli movl $(__BOOT_DS), %eax movl %eax, %ds movl %eax, %es movl %eax, %ss 1: /* * 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 $1b, %ebp /* setup a stack and make sure cpu supports long mode. */ movl $boot_stack_end, %eax addl %ebp, %eax movl %eax, %esp 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 movl BP_kernel_alignment(%esi), %eax decl %eax addl %eax, %ebx notl %eax andl %eax, %ebx cmpl $LOAD_PHYSICAL_ADDR, %ebx jge 1f #endif movl $LOAD_PHYSICAL_ADDR, %ebx 1: /* Target address to relocate to for decompression */ movl BP_init_size(%esi), %eax subl $_end, %eax addl %eax, %ebx /* * Prepare for entering 64 bit mode */ /* Load new GDT with the 64bit segments using 32bit descriptor */ addl %ebp, gdt+2(%ebp) lgdt gdt(%ebp) /* 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 insure that when the kernel is copied and decompressed * it will be done so encrypted. */ 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 */ 1: /* Initialize Page tables to 0 */ leal pgtable(%ebx), %edi xorl %eax, %eax movl $(BOOT_INIT_PGT_SIZE/4), %ecx rep stosl /* Build Level 4 */ leal pgtable + 0(%ebx), %edi leal 0x1007 (%edi), %eax movl %eax, 0(%edi) addl %edx, 4(%edi) /* Build Level 3 */ leal 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 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 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 /* * Setup for the jump to 64bit mode * * When the jump is performend 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. */ pushl $__KERNEL_CS leal startup_64(%ebp), %eax #ifdef CONFIG_EFI_MIXED movl efi32_boot_args(%ebp), %edi cmp $0, %edi jz 1f leal handover_entry(%ebp), %eax movl %esi, %edx movl efi32_boot_args+4(%ebp), %esi movl $0x0, %ecx 1: #endif pushl %eax /* Enter paged protected Mode, activating Long Mode */ movl $(X86_CR0_PG | X86_CR0_PE), %eax /* Enable Paging and Protected mode */ movl %eax, %cr0 /* Jump from 32bit compatibility mode into 64bit mode. */ lret SYM_FUNC_END(startup_32) #ifdef CONFIG_EFI_MIXED .org 0x190 SYM_FUNC_START(efi32_stub_entry) add $0x4, %esp /* Discard return address */ popl %ecx popl %edx popl %esi call 1f 1: pop %ebp subl $1b, %ebp movl %ecx, efi32_boot_args(%ebp) movl %edx, efi32_boot_args+4(%ebp) sgdtl efi32_boot_gdt(%ebp) /* Disable paging */ movl %cr0, %eax btrl $X86_CR0_PG_BIT, %eax movl %eax, %cr0 jmp startup_32 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. */ /* 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 movl BP_kernel_alignment(%rsi), %eax decl %eax addq %rax, %rbp notq %rax andq %rax, %rbp cmpq $LOAD_PHYSICAL_ADDR, %rbp jge 1f #endif movq $LOAD_PHYSICAL_ADDR, %rbp 1: /* Target address to relocate to for decompression */ movl BP_init_size(%rsi), %ebx subl $_end, %ebx addq %rbp, %rbx /* Set up the stack */ leaq boot_stack_end(%rbx), %rsp /* * paging_prepare() and cleanup_trampoline() below can have GOT * references. Adjust the table with address we are running at. * * Zero RAX for adjust_got: the GOT was not adjusted before; * there's no adjustment to undo. */ xorq %rax, %rax /* * Calculate the address the binary is loaded at and use it as * a GOT adjustment. */ call 1f 1: popq %rdi subq $1b, %rdi call .Ladjust_got /* * 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 gdt(%rip), %rax movq %rax, gdt64+2(%rip) lgdt gdt64(%rip) /* * 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 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 top_pgtable(%rbx), %rdi call cleanup_trampoline popq %rsi /* Zero EFLAGS */ pushq $0 popfq /* * Previously we've adjusted the GOT with address the binary was * loaded at. Now we need to re-adjust for relocation address. * * Calculate the address the binary is loaded at, so that we can * undo the previous GOT adjustment. */ call 1f 1: popq %rax subq $1b, %rax /* The new adjustment is the relocation address */ movq %rbx, %rdi call .Ladjust_got /* * Copy the compressed kernel to the end of our buffer * where decompression in place becomes safe. */ pushq %rsi leaq (_bss-8)(%rip), %rsi leaq (_bss-8)(%rbx), %rdi movq $_bss /* - $startup_32 */, %rcx shrq $3, %rcx std rep movsq cld popq %rsi /* * Jump to the relocated address. */ leaq .Lrelocated(%rbx), %rax jmp *%rax SYM_CODE_END(startup_64) #ifdef CONFIG_EFI_STUB .org 0x390 SYM_FUNC_START(efi64_stub_entry) SYM_FUNC_START_ALIAS(efi_stub_entry) movq $1, %rcx SYM_INNER_LABEL(handover_entry, SYM_L_LOCAL) and $~0xf, %rsp /* realign the stack */ call efi_main movq %rax,%rsi movl BP_code32_start(%esi), %eax leaq startup_64(%rax), %rax jmp *%rax SYM_FUNC_END(efi64_stub_entry) SYM_FUNC_END_ALIAS(efi_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 /* * 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 $z_input_len, %ecx /* input_len */ movq %rbp, %r8 /* output target address */ movq $z_output_len, %r9 /* 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) /* * Adjust the global offset table * * RAX is the previous adjustment of the table to undo (use 0 if it's the * first time we touch GOT). * RDI is the new adjustment to apply. */ .Ladjust_got: /* Walk through the GOT adding the address to the entries */ leaq _got(%rip), %rdx leaq _egot(%rip), %rcx 1: cmpq %rcx, %rdx jae 2f subq %rax, (%rdx) /* Undo previous adjustment */ addq %rdi, (%rdx) /* Apply the new adjustment */ addq $8, %rdx jmp 1b 2: ret .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 */ cmpl $0, %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 wrmsr popl %edx popl %ecx /* Enable PAE and LA57 (if required) paging modes */ movl $X86_CR4_PAE, %eax cmpl $0, %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 $(X86_CR0_PG | X86_CR0_PE), %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) #include "../../kernel/verify_cpu.S" .data SYM_DATA_START_LOCAL(gdt64) .word gdt_end - gdt .quad 0 SYM_DATA_END(gdt64) .balign 8 SYM_DATA_START_LOCAL(gdt) .word gdt_end - gdt .long gdt .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) #ifdef CONFIG_EFI_MIXED SYM_DATA_LOCAL(efi32_boot_args, .long 0, 0) #endif /* * 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 SYM_DATA_END_LABEL(boot_stack, SYM_L_LOCAL, boot_stack_end) /* * Space for page tables (not in .bss so not zeroed) */ .section ".pgtable","a",@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)