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 call paging_prepare 369 popq %rsi 370 371 /* Save the trampoline address in RCX */ 372 movq %rax, %rcx 373 374 /* 375 * Load the address of trampoline_return() into RDI. 376 * It will be used by the trampoline to return to the main code. 377 */ 378 leaq trampoline_return(%rip), %rdi 379 380 /* Switch to compatibility mode (CS.L = 0 CS.D = 1) via far return */ 381 pushq $__KERNEL32_CS 382 leaq TRAMPOLINE_32BIT_CODE_OFFSET(%rax), %rax 383 pushq %rax 384 lretq 385trampoline_return: 386 /* Restore the stack, the 32-bit trampoline uses its own stack */ 387 leaq boot_stack_end(%rbx), %rsp 388 389 /* 390 * cleanup_trampoline() would restore trampoline memory. 391 * 392 * RDI is address of the page table to use instead of page table 393 * in trampoline memory (if required). 394 * 395 * RSI holds real mode data and needs to be preserved across 396 * this function call. 397 */ 398 pushq %rsi 399 leaq top_pgtable(%rbx), %rdi 400 call cleanup_trampoline 401 popq %rsi 402 403 /* Zero EFLAGS */ 404 pushq $0 405 popfq 406 407 /* 408 * Previously we've adjusted the GOT with address the binary was 409 * loaded at. Now we need to re-adjust for relocation address. 410 * 411 * Calculate the address the binary is loaded at, so that we can 412 * undo the previous GOT adjustment. 413 */ 414 call 1f 4151: popq %rax 416 subq $1b, %rax 417 418 /* The new adjustment is the relocation address */ 419 movq %rbx, %rdi 420 call adjust_got 421 422/* 423 * Copy the compressed kernel to the end of our buffer 424 * where decompression in place becomes safe. 425 */ 426 pushq %rsi 427 leaq (_bss-8)(%rip), %rsi 428 leaq (_bss-8)(%rbx), %rdi 429 movq $_bss /* - $startup_32 */, %rcx 430 shrq $3, %rcx 431 std 432 rep movsq 433 cld 434 popq %rsi 435 436/* 437 * Jump to the relocated address. 438 */ 439 leaq relocated(%rbx), %rax 440 jmp *%rax 441 442#ifdef CONFIG_EFI_STUB 443 444/* The entry point for the PE/COFF executable is efi_pe_entry. */ 445ENTRY(efi_pe_entry) 446 movq %rcx, efi64_config(%rip) /* Handle */ 447 movq %rdx, efi64_config+8(%rip) /* EFI System table pointer */ 448 449 leaq efi64_config(%rip), %rax 450 movq %rax, efi_config(%rip) 451 452 call 1f 4531: popq %rbp 454 subq $1b, %rbp 455 456 /* 457 * Relocate efi_config->call(). 458 */ 459 addq %rbp, efi64_config+40(%rip) 460 461 movq %rax, %rdi 462 call make_boot_params 463 cmpq $0,%rax 464 je fail 465 mov %rax, %rsi 466 leaq startup_32(%rip), %rax 467 movl %eax, BP_code32_start(%rsi) 468 jmp 2f /* Skip the relocation */ 469 470handover_entry: 471 call 1f 4721: popq %rbp 473 subq $1b, %rbp 474 475 /* 476 * Relocate efi_config->call(). 477 */ 478 movq efi_config(%rip), %rax 479 addq %rbp, 40(%rax) 4802: 481 movq efi_config(%rip), %rdi 482 call efi_main 483 movq %rax,%rsi 484 cmpq $0,%rax 485 jne 2f 486fail: 487 /* EFI init failed, so hang. */ 488 hlt 489 jmp fail 4902: 491 movl BP_code32_start(%esi), %eax 492 leaq startup_64(%rax), %rax 493 jmp *%rax 494ENDPROC(efi_pe_entry) 495 496 .org 0x390 497ENTRY(efi64_stub_entry) 498 movq %rdi, efi64_config(%rip) /* Handle */ 499 movq %rsi, efi64_config+8(%rip) /* EFI System table pointer */ 500 501 leaq efi64_config(%rip), %rax 502 movq %rax, efi_config(%rip) 503 504 movq %rdx, %rsi 505 jmp handover_entry 506ENDPROC(efi64_stub_entry) 507#endif 508 509 .text 510relocated: 511 512/* 513 * Clear BSS (stack is currently empty) 514 */ 515 xorl %eax, %eax 516 leaq _bss(%rip), %rdi 517 leaq _ebss(%rip), %rcx 518 subq %rdi, %rcx 519 shrq $3, %rcx 520 rep stosq 521 522/* 523 * Do the extraction, and jump to the new kernel.. 524 */ 525 pushq %rsi /* Save the real mode argument */ 526 movq %rsi, %rdi /* real mode address */ 527 leaq boot_heap(%rip), %rsi /* malloc area for uncompression */ 528 leaq input_data(%rip), %rdx /* input_data */ 529 movl $z_input_len, %ecx /* input_len */ 530 movq %rbp, %r8 /* output target address */ 531 movq $z_output_len, %r9 /* decompressed length, end of relocs */ 532 call extract_kernel /* returns kernel location in %rax */ 533 popq %rsi 534 535/* 536 * Jump to the decompressed kernel. 537 */ 538 jmp *%rax 539 540/* 541 * Adjust the global offset table 542 * 543 * RAX is the previous adjustment of the table to undo (use 0 if it's the 544 * first time we touch GOT). 545 * RDI is the new adjustment to apply. 546 */ 547adjust_got: 548 /* Walk through the GOT adding the address to the entries */ 549 leaq _got(%rip), %rdx 550 leaq _egot(%rip), %rcx 5511: 552 cmpq %rcx, %rdx 553 jae 2f 554 subq %rax, (%rdx) /* Undo previous adjustment */ 555 addq %rdi, (%rdx) /* Apply the new adjustment */ 556 addq $8, %rdx 557 jmp 1b 5582: 559 ret 560 561 .code32 562/* 563 * This is the 32-bit trampoline that will be copied over to low memory. 564 * 565 * RDI contains the return address (might be above 4G). 566 * ECX contains the base address of the trampoline memory. 567 * Non zero RDX on return means we need to enable 5-level paging. 568 */ 569ENTRY(trampoline_32bit_src) 570 /* Set up data and stack segments */ 571 movl $__KERNEL_DS, %eax 572 movl %eax, %ds 573 movl %eax, %ss 574 575 /* Set up new stack */ 576 leal TRAMPOLINE_32BIT_STACK_END(%ecx), %esp 577 578 /* Disable paging */ 579 movl %cr0, %eax 580 btrl $X86_CR0_PG_BIT, %eax 581 movl %eax, %cr0 582 583 /* Check what paging mode we want to be in after the trampoline */ 584 cmpl $0, %edx 585 jz 1f 586 587 /* We want 5-level paging: don't touch CR3 if it already points to 5-level page tables */ 588 movl %cr4, %eax 589 testl $X86_CR4_LA57, %eax 590 jnz 3f 591 jmp 2f 5921: 593 /* We want 4-level paging: don't touch CR3 if it already points to 4-level page tables */ 594 movl %cr4, %eax 595 testl $X86_CR4_LA57, %eax 596 jz 3f 5972: 598 /* Point CR3 to the trampoline's new top level page table */ 599 leal TRAMPOLINE_32BIT_PGTABLE_OFFSET(%ecx), %eax 600 movl %eax, %cr3 6013: 602 /* Enable PAE and LA57 (if required) paging modes */ 603 movl $X86_CR4_PAE, %eax 604 cmpl $0, %edx 605 jz 1f 606 orl $X86_CR4_LA57, %eax 6071: 608 movl %eax, %cr4 609 610 /* Calculate address of paging_enabled() once we are executing in the trampoline */ 611 leal paging_enabled - trampoline_32bit_src + TRAMPOLINE_32BIT_CODE_OFFSET(%ecx), %eax 612 613 /* Prepare the stack for far return to Long Mode */ 614 pushl $__KERNEL_CS 615 pushl %eax 616 617 /* Enable paging again */ 618 movl $(X86_CR0_PG | X86_CR0_PE), %eax 619 movl %eax, %cr0 620 621 lret 622 623 .code64 624paging_enabled: 625 /* Return from the trampoline */ 626 jmp *%rdi 627 628 /* 629 * The trampoline code has a size limit. 630 * Make sure we fail to compile if the trampoline code grows 631 * beyond TRAMPOLINE_32BIT_CODE_SIZE bytes. 632 */ 633 .org trampoline_32bit_src + TRAMPOLINE_32BIT_CODE_SIZE 634 635 .code32 636no_longmode: 637 /* This isn't an x86-64 CPU, so hang intentionally, we cannot continue */ 6381: 639 hlt 640 jmp 1b 641 642#include "../../kernel/verify_cpu.S" 643 644 .data 645gdt64: 646 .word gdt_end - gdt 647 .long 0 648 .word 0 649 .quad 0 650gdt: 651 .word gdt_end - gdt 652 .long gdt 653 .word 0 654 .quad 0x00cf9a000000ffff /* __KERNEL32_CS */ 655 .quad 0x00af9a000000ffff /* __KERNEL_CS */ 656 .quad 0x00cf92000000ffff /* __KERNEL_DS */ 657 .quad 0x0080890000000000 /* TS descriptor */ 658 .quad 0x0000000000000000 /* TS continued */ 659gdt_end: 660 661#ifdef CONFIG_EFI_STUB 662efi_config: 663 .quad 0 664 665#ifdef CONFIG_EFI_MIXED 666 .global efi32_config 667efi32_config: 668 .fill 5,8,0 669 .quad efi64_thunk 670 .byte 0 671#endif 672 673 .global efi64_config 674efi64_config: 675 .fill 5,8,0 676 .quad efi_call 677 .byte 1 678#endif /* CONFIG_EFI_STUB */ 679 680/* 681 * Stack and heap for uncompression 682 */ 683 .bss 684 .balign 4 685boot_heap: 686 .fill BOOT_HEAP_SIZE, 1, 0 687boot_stack: 688 .fill BOOT_STACK_SIZE, 1, 0 689boot_stack_end: 690 691/* 692 * Space for page tables (not in .bss so not zeroed) 693 */ 694 .section ".pgtable","a",@nobits 695 .balign 4096 696pgtable: 697 .fill BOOT_PGT_SIZE, 1, 0 698 699/* 700 * The page table is going to be used instead of page table in the trampoline 701 * memory. 702 */ 703top_pgtable: 704 .fill PAGE_SIZE, 1, 0 705