1/* SPDX-License-Identifier: GPL-2.0 */ 2/* 3 * linux/boot/head.S 4 * 5 * Copyright (C) 1991, 1992, 1993 Linus Torvalds 6 */ 7 8/* 9 * head.S contains the 32-bit startup code. 10 * 11 * NOTE!!! Startup happens at absolute address 0x00001000, which is also where 12 * the page directory will exist. The startup code will be overwritten by 13 * the page directory. [According to comments etc elsewhere on a compressed 14 * kernel it will end up at 0x1000 + 1Mb I hope so as I assume this. - AC] 15 * 16 * Page 0 is deliberately kept safe, since System Management Mode code in 17 * laptops may need to access the BIOS data stored there. This is also 18 * useful for future device drivers that either access the BIOS via VM86 19 * mode. 20 */ 21 22/* 23 * High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996 24 */ 25 .code32 26 .text 27 28#include <linux/init.h> 29#include <linux/linkage.h> 30#include <asm/segment.h> 31#include <asm/boot.h> 32#include <asm/msr.h> 33#include <asm/processor-flags.h> 34#include <asm/asm-offsets.h> 35#include <asm/bootparam.h> 36#include "pgtable.h" 37 38/* 39 * Locally defined symbols should be marked hidden: 40 */ 41 .hidden _bss 42 .hidden _ebss 43 .hidden _got 44 .hidden _egot 45 46 __HEAD 47 .code32 48ENTRY(startup_32) 49 /* 50 * 32bit entry is 0 and it is ABI so immutable! 51 * If we come here directly from a bootloader, 52 * kernel(text+data+bss+brk) ramdisk, zero_page, command line 53 * all need to be under the 4G limit. 54 */ 55 cld 56 /* 57 * Test KEEP_SEGMENTS flag to see if the bootloader is asking 58 * us to not reload segments 59 */ 60 testb $KEEP_SEGMENTS, BP_loadflags(%esi) 61 jnz 1f 62 63 cli 64 movl $(__BOOT_DS), %eax 65 movl %eax, %ds 66 movl %eax, %es 67 movl %eax, %ss 681: 69 70/* 71 * Calculate the delta between where we were compiled to run 72 * at and where we were actually loaded at. This can only be done 73 * with a short local call on x86. Nothing else will tell us what 74 * address we are running at. The reserved chunk of the real-mode 75 * data at 0x1e4 (defined as a scratch field) are used as the stack 76 * for this calculation. Only 4 bytes are needed. 77 */ 78 leal (BP_scratch+4)(%esi), %esp 79 call 1f 801: popl %ebp 81 subl $1b, %ebp 82 83/* setup a stack and make sure cpu supports long mode. */ 84 movl $boot_stack_end, %eax 85 addl %ebp, %eax 86 movl %eax, %esp 87 88 call verify_cpu 89 testl %eax, %eax 90 jnz no_longmode 91 92/* 93 * Compute the delta between where we were compiled to run at 94 * and where the code will actually run at. 95 * 96 * %ebp contains the address we are loaded at by the boot loader and %ebx 97 * contains the address where we should move the kernel image temporarily 98 * for safe in-place decompression. 99 */ 100 101#ifdef CONFIG_RELOCATABLE 102 movl %ebp, %ebx 103 movl BP_kernel_alignment(%esi), %eax 104 decl %eax 105 addl %eax, %ebx 106 notl %eax 107 andl %eax, %ebx 108 cmpl $LOAD_PHYSICAL_ADDR, %ebx 109 jge 1f 110#endif 111 movl $LOAD_PHYSICAL_ADDR, %ebx 1121: 113 114 /* Target address to relocate to for decompression */ 115 movl BP_init_size(%esi), %eax 116 subl $_end, %eax 117 addl %eax, %ebx 118 119/* 120 * Prepare for entering 64 bit mode 121 */ 122 123 /* Load new GDT with the 64bit segments using 32bit descriptor */ 124 addl %ebp, gdt+2(%ebp) 125 lgdt gdt(%ebp) 126 127 /* Enable PAE mode */ 128 movl %cr4, %eax 129 orl $X86_CR4_PAE, %eax 130 movl %eax, %cr4 131 132 /* 133 * Build early 4G boot pagetable 134 */ 135 /* 136 * If SEV is active then set the encryption mask in the page tables. 137 * This will insure that when the kernel is copied and decompressed 138 * it will be done so encrypted. 139 */ 140 call get_sev_encryption_bit 141 xorl %edx, %edx 142 testl %eax, %eax 143 jz 1f 144 subl $32, %eax /* Encryption bit is always above bit 31 */ 145 bts %eax, %edx /* Set encryption mask for page tables */ 1461: 147 148 /* Initialize Page tables to 0 */ 149 leal pgtable(%ebx), %edi 150 xorl %eax, %eax 151 movl $(BOOT_INIT_PGT_SIZE/4), %ecx 152 rep stosl 153 154 /* Build Level 4 */ 155 leal pgtable + 0(%ebx), %edi 156 leal 0x1007 (%edi), %eax 157 movl %eax, 0(%edi) 158 addl %edx, 4(%edi) 159 160 /* Build Level 3 */ 161 leal pgtable + 0x1000(%ebx), %edi 162 leal 0x1007(%edi), %eax 163 movl $4, %ecx 1641: movl %eax, 0x00(%edi) 165 addl %edx, 0x04(%edi) 166 addl $0x00001000, %eax 167 addl $8, %edi 168 decl %ecx 169 jnz 1b 170 171 /* Build Level 2 */ 172 leal pgtable + 0x2000(%ebx), %edi 173 movl $0x00000183, %eax 174 movl $2048, %ecx 1751: movl %eax, 0(%edi) 176 addl %edx, 4(%edi) 177 addl $0x00200000, %eax 178 addl $8, %edi 179 decl %ecx 180 jnz 1b 181 182 /* Enable the boot page tables */ 183 leal pgtable(%ebx), %eax 184 movl %eax, %cr3 185 186 /* Enable Long mode in EFER (Extended Feature Enable Register) */ 187 movl $MSR_EFER, %ecx 188 rdmsr 189 btsl $_EFER_LME, %eax 190 wrmsr 191 192 /* After gdt is loaded */ 193 xorl %eax, %eax 194 lldt %ax 195 movl $__BOOT_TSS, %eax 196 ltr %ax 197 198 /* 199 * Setup for the jump to 64bit mode 200 * 201 * When the jump is performend we will be in long mode but 202 * in 32bit compatibility mode with EFER.LME = 1, CS.L = 0, CS.D = 1 203 * (and in turn EFER.LMA = 1). To jump into 64bit mode we use 204 * the new gdt/idt that has __KERNEL_CS with CS.L = 1. 205 * We place all of the values on our mini stack so lret can 206 * used to perform that far jump. 207 */ 208 pushl $__KERNEL_CS 209 leal startup_64(%ebp), %eax 210#ifdef CONFIG_EFI_MIXED 211 movl efi32_config(%ebp), %ebx 212 cmp $0, %ebx 213 jz 1f 214 leal handover_entry(%ebp), %eax 2151: 216#endif 217 pushl %eax 218 219 /* Enter paged protected Mode, activating Long Mode */ 220 movl $(X86_CR0_PG | X86_CR0_PE), %eax /* Enable Paging and Protected mode */ 221 movl %eax, %cr0 222 223 /* Jump from 32bit compatibility mode into 64bit mode. */ 224 lret 225ENDPROC(startup_32) 226 227#ifdef CONFIG_EFI_MIXED 228 .org 0x190 229ENTRY(efi32_stub_entry) 230 add $0x4, %esp /* Discard return address */ 231 popl %ecx 232 popl %edx 233 popl %esi 234 235 leal (BP_scratch+4)(%esi), %esp 236 call 1f 2371: pop %ebp 238 subl $1b, %ebp 239 240 movl %ecx, efi32_config(%ebp) 241 movl %edx, efi32_config+8(%ebp) 242 sgdtl efi32_boot_gdt(%ebp) 243 244 leal efi32_config(%ebp), %eax 245 movl %eax, efi_config(%ebp) 246 247 jmp startup_32 248ENDPROC(efi32_stub_entry) 249#endif 250 251 .code64 252 .org 0x200 253ENTRY(startup_64) 254 /* 255 * 64bit entry is 0x200 and it is ABI so immutable! 256 * We come here either from startup_32 or directly from a 257 * 64bit bootloader. 258 * If we come here from a bootloader, kernel(text+data+bss+brk), 259 * ramdisk, zero_page, command line could be above 4G. 260 * We depend on an identity mapped page table being provided 261 * that maps our entire kernel(text+data+bss+brk), zero page 262 * and command line. 263 */ 264 265 /* Setup data segments. */ 266 xorl %eax, %eax 267 movl %eax, %ds 268 movl %eax, %es 269 movl %eax, %ss 270 movl %eax, %fs 271 movl %eax, %gs 272 273 /* 274 * Compute the decompressed kernel start address. It is where 275 * we were loaded at aligned to a 2M boundary. %rbp contains the 276 * decompressed kernel start address. 277 * 278 * If it is a relocatable kernel then decompress and run the kernel 279 * from load address aligned to 2MB addr, otherwise decompress and 280 * run the kernel from LOAD_PHYSICAL_ADDR 281 * 282 * We cannot rely on the calculation done in 32-bit mode, since we 283 * may have been invoked via the 64-bit entry point. 284 */ 285 286 /* Start with the delta to where the kernel will run at. */ 287#ifdef CONFIG_RELOCATABLE 288 leaq startup_32(%rip) /* - $startup_32 */, %rbp 289 movl BP_kernel_alignment(%rsi), %eax 290 decl %eax 291 addq %rax, %rbp 292 notq %rax 293 andq %rax, %rbp 294 cmpq $LOAD_PHYSICAL_ADDR, %rbp 295 jge 1f 296#endif 297 movq $LOAD_PHYSICAL_ADDR, %rbp 2981: 299 300 /* Target address to relocate to for decompression */ 301 movl BP_init_size(%rsi), %ebx 302 subl $_end, %ebx 303 addq %rbp, %rbx 304 305 /* Set up the stack */ 306 leaq boot_stack_end(%rbx), %rsp 307 308 /* 309 * paging_prepare() and cleanup_trampoline() below can have GOT 310 * references. Adjust the table with address we are running at. 311 * 312 * Zero RAX for adjust_got: the GOT was not adjusted before; 313 * there's no adjustment to undo. 314 */ 315 xorq %rax, %rax 316 317 /* 318 * Calculate the address the binary is loaded at and use it as 319 * a GOT adjustment. 320 */ 321 call 1f 3221: popq %rdi 323 subq $1b, %rdi 324 325 call adjust_got 326 327 /* 328 * At this point we are in long mode with 4-level paging enabled, 329 * but we might want to enable 5-level paging or vice versa. 330 * 331 * The problem is that we cannot do it directly. Setting or clearing 332 * CR4.LA57 in long mode would trigger #GP. So we need to switch off 333 * long mode and paging first. 334 * 335 * We also need a trampoline in lower memory to switch over from 336 * 4- to 5-level paging for cases when the bootloader puts the kernel 337 * above 4G, but didn't enable 5-level paging for us. 338 * 339 * The same trampoline can be used to switch from 5- to 4-level paging 340 * mode, like when starting 4-level paging kernel via kexec() when 341 * original kernel worked in 5-level paging mode. 342 * 343 * For the trampoline, we need the top page table to reside in lower 344 * memory as we don't have a way to load 64-bit values into CR3 in 345 * 32-bit mode. 346 * 347 * We go though the trampoline even if we don't have to: if we're 348 * already in a desired paging mode. This way the trampoline code gets 349 * tested on every boot. 350 */ 351 352 /* Make sure we have GDT with 32-bit code segment */ 353 leaq gdt(%rip), %rax 354 movq %rax, gdt64+2(%rip) 355 lgdt gdt64(%rip) 356 357 /* 358 * paging_prepare() sets up the trampoline and checks if we need to 359 * enable 5-level paging. 360 * 361 * Address of the trampoline is returned in RAX. 362 * Non zero RDX on return means we need to enable 5-level paging. 363 * 364 * RSI holds real mode data and needs to be preserved across 365 * this function call. 366 */ 367 pushq %rsi 368 movq %rsi, %rdi /* real mode address */ 369 call paging_prepare 370 popq %rsi 371 372 /* Save the trampoline address in RCX */ 373 movq %rax, %rcx 374 375 /* 376 * Load the address of trampoline_return() into RDI. 377 * It will be used by the trampoline to return to the main code. 378 */ 379 leaq trampoline_return(%rip), %rdi 380 381 /* Switch to compatibility mode (CS.L = 0 CS.D = 1) via far return */ 382 pushq $__KERNEL32_CS 383 leaq TRAMPOLINE_32BIT_CODE_OFFSET(%rax), %rax 384 pushq %rax 385 lretq 386trampoline_return: 387 /* Restore the stack, the 32-bit trampoline uses its own stack */ 388 leaq boot_stack_end(%rbx), %rsp 389 390 /* 391 * cleanup_trampoline() would restore trampoline memory. 392 * 393 * RDI is address of the page table to use instead of page table 394 * in trampoline memory (if required). 395 * 396 * RSI holds real mode data and needs to be preserved across 397 * this function call. 398 */ 399 pushq %rsi 400 leaq top_pgtable(%rbx), %rdi 401 call cleanup_trampoline 402 popq %rsi 403 404 /* Zero EFLAGS */ 405 pushq $0 406 popfq 407 408 /* 409 * Previously we've adjusted the GOT with address the binary was 410 * loaded at. Now we need to re-adjust for relocation address. 411 * 412 * Calculate the address the binary is loaded at, so that we can 413 * undo the previous GOT adjustment. 414 */ 415 call 1f 4161: popq %rax 417 subq $1b, %rax 418 419 /* The new adjustment is the relocation address */ 420 movq %rbx, %rdi 421 call adjust_got 422 423/* 424 * Copy the compressed kernel to the end of our buffer 425 * where decompression in place becomes safe. 426 */ 427 pushq %rsi 428 leaq (_bss-8)(%rip), %rsi 429 leaq (_bss-8)(%rbx), %rdi 430 movq $_bss /* - $startup_32 */, %rcx 431 shrq $3, %rcx 432 std 433 rep movsq 434 cld 435 popq %rsi 436 437/* 438 * Jump to the relocated address. 439 */ 440 leaq relocated(%rbx), %rax 441 jmp *%rax 442 443#ifdef CONFIG_EFI_STUB 444 445/* The entry point for the PE/COFF executable is efi_pe_entry. */ 446ENTRY(efi_pe_entry) 447 movq %rcx, efi64_config(%rip) /* Handle */ 448 movq %rdx, efi64_config+8(%rip) /* EFI System table pointer */ 449 450 leaq efi64_config(%rip), %rax 451 movq %rax, efi_config(%rip) 452 453 call 1f 4541: popq %rbp 455 subq $1b, %rbp 456 457 /* 458 * Relocate efi_config->call(). 459 */ 460 addq %rbp, efi64_config+40(%rip) 461 462 movq %rax, %rdi 463 call make_boot_params 464 cmpq $0,%rax 465 je fail 466 mov %rax, %rsi 467 leaq startup_32(%rip), %rax 468 movl %eax, BP_code32_start(%rsi) 469 jmp 2f /* Skip the relocation */ 470 471handover_entry: 472 call 1f 4731: popq %rbp 474 subq $1b, %rbp 475 476 /* 477 * Relocate efi_config->call(). 478 */ 479 movq efi_config(%rip), %rax 480 addq %rbp, 40(%rax) 4812: 482 movq efi_config(%rip), %rdi 483 call efi_main 484 movq %rax,%rsi 485 cmpq $0,%rax 486 jne 2f 487fail: 488 /* EFI init failed, so hang. */ 489 hlt 490 jmp fail 4912: 492 movl BP_code32_start(%esi), %eax 493 leaq startup_64(%rax), %rax 494 jmp *%rax 495ENDPROC(efi_pe_entry) 496 497 .org 0x390 498ENTRY(efi64_stub_entry) 499 movq %rdi, efi64_config(%rip) /* Handle */ 500 movq %rsi, efi64_config+8(%rip) /* EFI System table pointer */ 501 502 leaq efi64_config(%rip), %rax 503 movq %rax, efi_config(%rip) 504 505 movq %rdx, %rsi 506 jmp handover_entry 507ENDPROC(efi64_stub_entry) 508#endif 509 510 .text 511relocated: 512 513/* 514 * Clear BSS (stack is currently empty) 515 */ 516 xorl %eax, %eax 517 leaq _bss(%rip), %rdi 518 leaq _ebss(%rip), %rcx 519 subq %rdi, %rcx 520 shrq $3, %rcx 521 rep stosq 522 523/* 524 * Do the extraction, and jump to the new kernel.. 525 */ 526 pushq %rsi /* Save the real mode argument */ 527 movq %rsi, %rdi /* real mode address */ 528 leaq boot_heap(%rip), %rsi /* malloc area for uncompression */ 529 leaq input_data(%rip), %rdx /* input_data */ 530 movl $z_input_len, %ecx /* input_len */ 531 movq %rbp, %r8 /* output target address */ 532 movq $z_output_len, %r9 /* decompressed length, end of relocs */ 533 call extract_kernel /* returns kernel location in %rax */ 534 popq %rsi 535 536/* 537 * Jump to the decompressed kernel. 538 */ 539 jmp *%rax 540 541/* 542 * Adjust the global offset table 543 * 544 * RAX is the previous adjustment of the table to undo (use 0 if it's the 545 * first time we touch GOT). 546 * RDI is the new adjustment to apply. 547 */ 548adjust_got: 549 /* Walk through the GOT adding the address to the entries */ 550 leaq _got(%rip), %rdx 551 leaq _egot(%rip), %rcx 5521: 553 cmpq %rcx, %rdx 554 jae 2f 555 subq %rax, (%rdx) /* Undo previous adjustment */ 556 addq %rdi, (%rdx) /* Apply the new adjustment */ 557 addq $8, %rdx 558 jmp 1b 5592: 560 ret 561 562 .code32 563/* 564 * This is the 32-bit trampoline that will be copied over to low memory. 565 * 566 * RDI contains the return address (might be above 4G). 567 * ECX contains the base address of the trampoline memory. 568 * Non zero RDX on return means we need to enable 5-level paging. 569 */ 570ENTRY(trampoline_32bit_src) 571 /* Set up data and stack segments */ 572 movl $__KERNEL_DS, %eax 573 movl %eax, %ds 574 movl %eax, %ss 575 576 /* Set up new stack */ 577 leal TRAMPOLINE_32BIT_STACK_END(%ecx), %esp 578 579 /* Disable paging */ 580 movl %cr0, %eax 581 btrl $X86_CR0_PG_BIT, %eax 582 movl %eax, %cr0 583 584 /* Check what paging mode we want to be in after the trampoline */ 585 cmpl $0, %edx 586 jz 1f 587 588 /* We want 5-level paging: don't touch CR3 if it already points to 5-level page tables */ 589 movl %cr4, %eax 590 testl $X86_CR4_LA57, %eax 591 jnz 3f 592 jmp 2f 5931: 594 /* We want 4-level paging: don't touch CR3 if it already points to 4-level page tables */ 595 movl %cr4, %eax 596 testl $X86_CR4_LA57, %eax 597 jz 3f 5982: 599 /* Point CR3 to the trampoline's new top level page table */ 600 leal TRAMPOLINE_32BIT_PGTABLE_OFFSET(%ecx), %eax 601 movl %eax, %cr3 6023: 603 /* Enable PAE and LA57 (if required) paging modes */ 604 movl $X86_CR4_PAE, %eax 605 cmpl $0, %edx 606 jz 1f 607 orl $X86_CR4_LA57, %eax 6081: 609 movl %eax, %cr4 610 611 /* Calculate address of paging_enabled() once we are executing in the trampoline */ 612 leal paging_enabled - trampoline_32bit_src + TRAMPOLINE_32BIT_CODE_OFFSET(%ecx), %eax 613 614 /* Prepare the stack for far return to Long Mode */ 615 pushl $__KERNEL_CS 616 pushl %eax 617 618 /* Enable paging again */ 619 movl $(X86_CR0_PG | X86_CR0_PE), %eax 620 movl %eax, %cr0 621 622 lret 623 624 .code64 625paging_enabled: 626 /* Return from the trampoline */ 627 jmp *%rdi 628 629 /* 630 * The trampoline code has a size limit. 631 * Make sure we fail to compile if the trampoline code grows 632 * beyond TRAMPOLINE_32BIT_CODE_SIZE bytes. 633 */ 634 .org trampoline_32bit_src + TRAMPOLINE_32BIT_CODE_SIZE 635 636 .code32 637no_longmode: 638 /* This isn't an x86-64 CPU, so hang intentionally, we cannot continue */ 6391: 640 hlt 641 jmp 1b 642 643#include "../../kernel/verify_cpu.S" 644 645 .data 646gdt64: 647 .word gdt_end - gdt 648 .long 0 649 .word 0 650 .quad 0 651gdt: 652 .word gdt_end - gdt 653 .long gdt 654 .word 0 655 .quad 0x00cf9a000000ffff /* __KERNEL32_CS */ 656 .quad 0x00af9a000000ffff /* __KERNEL_CS */ 657 .quad 0x00cf92000000ffff /* __KERNEL_DS */ 658 .quad 0x0080890000000000 /* TS descriptor */ 659 .quad 0x0000000000000000 /* TS continued */ 660gdt_end: 661 662#ifdef CONFIG_EFI_STUB 663efi_config: 664 .quad 0 665 666#ifdef CONFIG_EFI_MIXED 667 .global efi32_config 668efi32_config: 669 .fill 5,8,0 670 .quad efi64_thunk 671 .byte 0 672#endif 673 674 .global efi64_config 675efi64_config: 676 .fill 5,8,0 677 .quad efi_call 678 .byte 1 679#endif /* CONFIG_EFI_STUB */ 680 681/* 682 * Stack and heap for uncompression 683 */ 684 .bss 685 .balign 4 686boot_heap: 687 .fill BOOT_HEAP_SIZE, 1, 0 688boot_stack: 689 .fill BOOT_STACK_SIZE, 1, 0 690boot_stack_end: 691 692/* 693 * Space for page tables (not in .bss so not zeroed) 694 */ 695 .section ".pgtable","a",@nobits 696 .balign 4096 697pgtable: 698 .fill BOOT_PGT_SIZE, 1, 0 699 700/* 701 * The page table is going to be used instead of page table in the trampoline 702 * memory. 703 */ 704top_pgtable: 705 .fill PAGE_SIZE, 1, 0 706