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 <asm/desc_defs.h> 37 #include <asm/trapnr.h> 38 #include "pgtable.h" 39 40 /* 41 * Fix alignment at 16 bytes. Following CONFIG_FUNCTION_ALIGNMENT will result 42 * in assembly errors due to trying to move .org backward due to the excessive 43 * alignment. 44 */ 45 #undef __ALIGN 46 #define __ALIGN .balign 16, 0x90 47 48 /* 49 * Locally defined symbols should be marked hidden: 50 */ 51 .hidden _bss 52 .hidden _ebss 53 .hidden _end 54 55 __HEAD 56 57 /* 58 * This macro gives the relative virtual address of X, i.e. the offset of X 59 * from startup_32. This is the same as the link-time virtual address of X, 60 * since startup_32 is at 0, but defining it this way tells the 61 * assembler/linker that we do not want the actual run-time address of X. This 62 * prevents the linker from trying to create unwanted run-time relocation 63 * entries for the reference when the compressed kernel is linked as PIE. 64 * 65 * A reference X(%reg) will result in the link-time VA of X being stored with 66 * the instruction, and a run-time R_X86_64_RELATIVE relocation entry that 67 * adds the 64-bit base address where the kernel is loaded. 68 * 69 * Replacing it with (X-startup_32)(%reg) results in the offset being stored, 70 * and no run-time relocation. 71 * 72 * The macro should be used as a displacement with a base register containing 73 * the run-time address of startup_32 [i.e. rva(X)(%reg)], or as an immediate 74 * [$ rva(X)]. 75 * 76 * This macro can only be used from within the .head.text section, since the 77 * expression requires startup_32 to be in the same section as the code being 78 * assembled. 79 */ 80 #define rva(X) ((X) - startup_32) 81 82 .code32 83 SYM_FUNC_START(startup_32) 84 /* 85 * 32bit entry is 0 and it is ABI so immutable! 86 * If we come here directly from a bootloader, 87 * kernel(text+data+bss+brk) ramdisk, zero_page, command line 88 * all need to be under the 4G limit. 89 */ 90 cld 91 cli 92 93 /* 94 * Calculate the delta between where we were compiled to run 95 * at and where we were actually loaded at. This can only be done 96 * with a short local call on x86. Nothing else will tell us what 97 * address we are running at. The reserved chunk of the real-mode 98 * data at 0x1e4 (defined as a scratch field) are used as the stack 99 * for this calculation. Only 4 bytes are needed. 100 */ 101 leal (BP_scratch+4)(%esi), %esp 102 call 1f 103 1: popl %ebp 104 subl $ rva(1b), %ebp 105 106 /* Load new GDT with the 64bit segments using 32bit descriptor */ 107 leal rva(gdt)(%ebp), %eax 108 movl %eax, 2(%eax) 109 lgdt (%eax) 110 111 /* Load segment registers with our descriptors */ 112 movl $__BOOT_DS, %eax 113 movl %eax, %ds 114 movl %eax, %es 115 movl %eax, %fs 116 movl %eax, %gs 117 movl %eax, %ss 118 119 /* Setup a stack and load CS from current GDT */ 120 leal rva(boot_stack_end)(%ebp), %esp 121 122 pushl $__KERNEL32_CS 123 leal rva(1f)(%ebp), %eax 124 pushl %eax 125 lretl 126 1: 127 128 /* Setup Exception handling for SEV-ES */ 129 #ifdef CONFIG_AMD_MEM_ENCRYPT 130 call startup32_load_idt 131 #endif 132 133 /* Make sure cpu supports long mode. */ 134 call verify_cpu 135 testl %eax, %eax 136 jnz .Lno_longmode 137 138 /* 139 * Compute the delta between where we were compiled to run at 140 * and where the code will actually run at. 141 * 142 * %ebp contains the address we are loaded at by the boot loader and %ebx 143 * contains the address where we should move the kernel image temporarily 144 * for safe in-place decompression. 145 */ 146 147 #ifdef CONFIG_RELOCATABLE 148 movl %ebp, %ebx 149 movl BP_kernel_alignment(%esi), %eax 150 decl %eax 151 addl %eax, %ebx 152 notl %eax 153 andl %eax, %ebx 154 cmpl $LOAD_PHYSICAL_ADDR, %ebx 155 jae 1f 156 #endif 157 movl $LOAD_PHYSICAL_ADDR, %ebx 158 1: 159 160 /* Target address to relocate to for decompression */ 161 addl BP_init_size(%esi), %ebx 162 subl $ rva(_end), %ebx 163 164 /* 165 * Prepare for entering 64 bit mode 166 */ 167 168 /* Enable PAE mode */ 169 movl %cr4, %eax 170 orl $X86_CR4_PAE, %eax 171 movl %eax, %cr4 172 173 /* 174 * Build early 4G boot pagetable 175 */ 176 /* 177 * If SEV is active then set the encryption mask in the page tables. 178 * This will ensure that when the kernel is copied and decompressed 179 * it will be done so encrypted. 180 */ 181 xorl %edx, %edx 182 #ifdef CONFIG_AMD_MEM_ENCRYPT 183 call get_sev_encryption_bit 184 xorl %edx, %edx 185 testl %eax, %eax 186 jz 1f 187 subl $32, %eax /* Encryption bit is always above bit 31 */ 188 bts %eax, %edx /* Set encryption mask for page tables */ 189 /* 190 * Set MSR_AMD64_SEV_ENABLED_BIT in sev_status so that 191 * startup32_check_sev_cbit() will do a check. sev_enable() will 192 * initialize sev_status with all the bits reported by 193 * MSR_AMD_SEV_STATUS later, but only MSR_AMD64_SEV_ENABLED_BIT 194 * needs to be set for now. 195 */ 196 movl $1, rva(sev_status)(%ebp) 197 1: 198 #endif 199 200 /* Initialize Page tables to 0 */ 201 leal rva(pgtable)(%ebx), %edi 202 xorl %eax, %eax 203 movl $(BOOT_INIT_PGT_SIZE/4), %ecx 204 rep stosl 205 206 /* Build Level 4 */ 207 leal rva(pgtable + 0)(%ebx), %edi 208 leal 0x1007 (%edi), %eax 209 movl %eax, 0(%edi) 210 addl %edx, 4(%edi) 211 212 /* Build Level 3 */ 213 leal rva(pgtable + 0x1000)(%ebx), %edi 214 leal 0x1007(%edi), %eax 215 movl $4, %ecx 216 1: movl %eax, 0x00(%edi) 217 addl %edx, 0x04(%edi) 218 addl $0x00001000, %eax 219 addl $8, %edi 220 decl %ecx 221 jnz 1b 222 223 /* Build Level 2 */ 224 leal rva(pgtable + 0x2000)(%ebx), %edi 225 movl $0x00000183, %eax 226 movl $2048, %ecx 227 1: movl %eax, 0(%edi) 228 addl %edx, 4(%edi) 229 addl $0x00200000, %eax 230 addl $8, %edi 231 decl %ecx 232 jnz 1b 233 234 /* Enable the boot page tables */ 235 leal rva(pgtable)(%ebx), %eax 236 movl %eax, %cr3 237 238 /* Enable Long mode in EFER (Extended Feature Enable Register) */ 239 movl $MSR_EFER, %ecx 240 rdmsr 241 btsl $_EFER_LME, %eax 242 wrmsr 243 244 /* After gdt is loaded */ 245 xorl %eax, %eax 246 lldt %ax 247 movl $__BOOT_TSS, %eax 248 ltr %ax 249 250 #ifdef CONFIG_AMD_MEM_ENCRYPT 251 /* Check if the C-bit position is correct when SEV is active */ 252 call startup32_check_sev_cbit 253 #endif 254 255 /* 256 * Setup for the jump to 64bit mode 257 * 258 * When the jump is performed we will be in long mode but 259 * in 32bit compatibility mode with EFER.LME = 1, CS.L = 0, CS.D = 1 260 * (and in turn EFER.LMA = 1). To jump into 64bit mode we use 261 * the new gdt/idt that has __KERNEL_CS with CS.L = 1. 262 * We place all of the values on our mini stack so lret can 263 * used to perform that far jump. 264 */ 265 leal rva(startup_64)(%ebp), %eax 266 #ifdef CONFIG_EFI_MIXED 267 cmpb $1, rva(efi_is64)(%ebp) 268 je 1f 269 leal rva(startup_64_mixed_mode)(%ebp), %eax 270 1: 271 #endif 272 273 pushl $__KERNEL_CS 274 pushl %eax 275 276 /* Enter paged protected Mode, activating Long Mode */ 277 movl $CR0_STATE, %eax 278 movl %eax, %cr0 279 280 /* Jump from 32bit compatibility mode into 64bit mode. */ 281 lret 282 SYM_FUNC_END(startup_32) 283 284 .code64 285 .org 0x200 286 SYM_CODE_START(startup_64) 287 /* 288 * 64bit entry is 0x200 and it is ABI so immutable! 289 * We come here either from startup_32 or directly from a 290 * 64bit bootloader. 291 * If we come here from a bootloader, kernel(text+data+bss+brk), 292 * ramdisk, zero_page, command line could be above 4G. 293 * We depend on an identity mapped page table being provided 294 * that maps our entire kernel(text+data+bss+brk), zero page 295 * and command line. 296 */ 297 298 cld 299 cli 300 301 /* Setup data segments. */ 302 xorl %eax, %eax 303 movl %eax, %ds 304 movl %eax, %es 305 movl %eax, %ss 306 movl %eax, %fs 307 movl %eax, %gs 308 309 /* 310 * Compute the decompressed kernel start address. It is where 311 * we were loaded at aligned to a 2M boundary. %rbp contains the 312 * decompressed kernel start address. 313 * 314 * If it is a relocatable kernel then decompress and run the kernel 315 * from load address aligned to 2MB addr, otherwise decompress and 316 * run the kernel from LOAD_PHYSICAL_ADDR 317 * 318 * We cannot rely on the calculation done in 32-bit mode, since we 319 * may have been invoked via the 64-bit entry point. 320 */ 321 322 /* Start with the delta to where the kernel will run at. */ 323 #ifdef CONFIG_RELOCATABLE 324 leaq startup_32(%rip) /* - $startup_32 */, %rbp 325 movl BP_kernel_alignment(%rsi), %eax 326 decl %eax 327 addq %rax, %rbp 328 notq %rax 329 andq %rax, %rbp 330 cmpq $LOAD_PHYSICAL_ADDR, %rbp 331 jae 1f 332 #endif 333 movq $LOAD_PHYSICAL_ADDR, %rbp 334 1: 335 336 /* Target address to relocate to for decompression */ 337 movl BP_init_size(%rsi), %ebx 338 subl $ rva(_end), %ebx 339 addq %rbp, %rbx 340 341 /* Set up the stack */ 342 leaq rva(boot_stack_end)(%rbx), %rsp 343 344 /* 345 * At this point we are in long mode with 4-level paging enabled, 346 * but we might want to enable 5-level paging or vice versa. 347 * 348 * The problem is that we cannot do it directly. Setting or clearing 349 * CR4.LA57 in long mode would trigger #GP. So we need to switch off 350 * long mode and paging first. 351 * 352 * We also need a trampoline in lower memory to switch over from 353 * 4- to 5-level paging for cases when the bootloader puts the kernel 354 * above 4G, but didn't enable 5-level paging for us. 355 * 356 * The same trampoline can be used to switch from 5- to 4-level paging 357 * mode, like when starting 4-level paging kernel via kexec() when 358 * original kernel worked in 5-level paging mode. 359 * 360 * For the trampoline, we need the top page table to reside in lower 361 * memory as we don't have a way to load 64-bit values into CR3 in 362 * 32-bit mode. 363 */ 364 365 /* Make sure we have GDT with 32-bit code segment */ 366 leaq gdt64(%rip), %rax 367 addq %rax, 2(%rax) 368 lgdt (%rax) 369 370 /* Reload CS so IRET returns to a CS actually in the GDT */ 371 pushq $__KERNEL_CS 372 leaq .Lon_kernel_cs(%rip), %rax 373 pushq %rax 374 lretq 375 376 .Lon_kernel_cs: 377 /* 378 * RSI holds a pointer to a boot_params structure provided by the 379 * loader, and this needs to be preserved across C function calls. So 380 * move it into a callee saved register. 381 */ 382 movq %rsi, %r15 383 384 call load_stage1_idt 385 386 #ifdef CONFIG_AMD_MEM_ENCRYPT 387 /* 388 * Now that the stage1 interrupt handlers are set up, #VC exceptions from 389 * CPUID instructions can be properly handled for SEV-ES guests. 390 * 391 * For SEV-SNP, the CPUID table also needs to be set up in advance of any 392 * CPUID instructions being issued, so go ahead and do that now via 393 * sev_enable(), which will also handle the rest of the SEV-related 394 * detection/setup to ensure that has been done in advance of any dependent 395 * code. Pass the boot_params pointer as the first argument. 396 */ 397 movq %r15, %rdi 398 call sev_enable 399 #endif 400 401 /* Preserve only the CR4 bits that must be preserved, and clear the rest */ 402 movq %cr4, %rax 403 andl $(X86_CR4_PAE | X86_CR4_MCE | X86_CR4_LA57), %eax 404 movq %rax, %cr4 405 406 /* 407 * configure_5level_paging() updates the number of paging levels using 408 * a trampoline in 32-bit addressable memory if the current number does 409 * not match the desired number. 410 * 411 * Pass the boot_params pointer as the first argument. The second 412 * argument is the relocated address of the page table to use instead 413 * of the page table in trampoline memory (if required). 414 */ 415 movq %r15, %rdi 416 leaq rva(top_pgtable)(%rbx), %rsi 417 call configure_5level_paging 418 419 /* Zero EFLAGS */ 420 pushq $0 421 popfq 422 423 /* 424 * Copy the compressed kernel to the end of our buffer 425 * where decompression in place becomes safe. 426 */ 427 leaq (_bss-8)(%rip), %rsi 428 leaq rva(_bss-8)(%rbx), %rdi 429 movl $(_bss - startup_32), %ecx 430 shrl $3, %ecx 431 std 432 rep movsq 433 cld 434 435 /* 436 * The GDT may get overwritten either during the copy we just did or 437 * during extract_kernel below. To avoid any issues, repoint the GDTR 438 * to the new copy of the GDT. 439 */ 440 leaq rva(gdt64)(%rbx), %rax 441 leaq rva(gdt)(%rbx), %rdx 442 movq %rdx, 2(%rax) 443 lgdt (%rax) 444 445 /* 446 * Jump to the relocated address. 447 */ 448 leaq rva(.Lrelocated)(%rbx), %rax 449 jmp *%rax 450 SYM_CODE_END(startup_64) 451 452 .text 453 SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated) 454 455 /* 456 * Clear BSS (stack is currently empty) 457 */ 458 xorl %eax, %eax 459 leaq _bss(%rip), %rdi 460 leaq _ebss(%rip), %rcx 461 subq %rdi, %rcx 462 shrq $3, %rcx 463 rep stosq 464 465 call load_stage2_idt 466 467 /* Pass boot_params to initialize_identity_maps() */ 468 movq %r15, %rdi 469 call initialize_identity_maps 470 471 /* 472 * Do the extraction, and jump to the new kernel.. 473 */ 474 /* pass struct boot_params pointer and output target address */ 475 movq %r15, %rdi 476 movq %rbp, %rsi 477 call extract_kernel /* returns kernel entry point in %rax */ 478 479 /* 480 * Jump to the decompressed kernel. 481 */ 482 movq %r15, %rsi 483 jmp *%rax 484 SYM_FUNC_END(.Lrelocated) 485 486 /* 487 * This is the 32-bit trampoline that will be copied over to low memory. It 488 * will be called using the ordinary 64-bit calling convention from code 489 * running in 64-bit mode. 490 * 491 * Return address is at the top of the stack (might be above 4G). 492 * The first argument (EDI) contains the address of the temporary PGD level 493 * page table in 32-bit addressable memory which will be programmed into 494 * register CR3. 495 */ 496 .section ".rodata", "a", @progbits 497 SYM_CODE_START(trampoline_32bit_src) 498 /* 499 * Preserve callee save 64-bit registers on the stack: this is 500 * necessary because the architecture does not guarantee that GPRs will 501 * retain their full 64-bit values across a 32-bit mode switch. 502 */ 503 pushq %r15 504 pushq %r14 505 pushq %r13 506 pushq %r12 507 pushq %rbp 508 pushq %rbx 509 510 /* Preserve top half of RSP in a legacy mode GPR to avoid truncation */ 511 movq %rsp, %rbx 512 shrq $32, %rbx 513 514 /* Switch to compatibility mode (CS.L = 0 CS.D = 1) via far return */ 515 pushq $__KERNEL32_CS 516 leaq 0f(%rip), %rax 517 pushq %rax 518 lretq 519 520 /* 521 * The 32-bit code below will do a far jump back to long mode and end 522 * up here after reconfiguring the number of paging levels. First, the 523 * stack pointer needs to be restored to its full 64-bit value before 524 * the callee save register contents can be popped from the stack. 525 */ 526 .Lret: 527 shlq $32, %rbx 528 orq %rbx, %rsp 529 530 /* Restore the preserved 64-bit registers */ 531 popq %rbx 532 popq %rbp 533 popq %r12 534 popq %r13 535 popq %r14 536 popq %r15 537 retq 538 539 .code32 540 0: 541 /* Disable paging */ 542 movl %cr0, %eax 543 btrl $X86_CR0_PG_BIT, %eax 544 movl %eax, %cr0 545 546 /* Point CR3 to the trampoline's new top level page table */ 547 movl %edi, %cr3 548 549 /* Set EFER.LME=1 as a precaution in case hypervsior pulls the rug */ 550 movl $MSR_EFER, %ecx 551 rdmsr 552 btsl $_EFER_LME, %eax 553 /* Avoid writing EFER if no change was made (for TDX guest) */ 554 jc 1f 555 wrmsr 556 1: 557 /* Toggle CR4.LA57 */ 558 movl %cr4, %eax 559 btcl $X86_CR4_LA57_BIT, %eax 560 movl %eax, %cr4 561 562 /* Enable paging again. */ 563 movl %cr0, %eax 564 btsl $X86_CR0_PG_BIT, %eax 565 movl %eax, %cr0 566 567 /* 568 * Return to the 64-bit calling code using LJMP rather than LRET, to 569 * avoid the need for a 32-bit addressable stack. The destination 570 * address will be adjusted after the template code is copied into a 571 * 32-bit addressable buffer. 572 */ 573 .Ljmp: ljmpl $__KERNEL_CS, $(.Lret - trampoline_32bit_src) 574 SYM_CODE_END(trampoline_32bit_src) 575 576 /* 577 * This symbol is placed right after trampoline_32bit_src() so its address can 578 * be used to infer the size of the trampoline code. 579 */ 580 SYM_DATA(trampoline_ljmp_imm_offset, .word .Ljmp + 1 - trampoline_32bit_src) 581 582 /* 583 * The trampoline code has a size limit. 584 * Make sure we fail to compile if the trampoline code grows 585 * beyond TRAMPOLINE_32BIT_CODE_SIZE bytes. 586 */ 587 .org trampoline_32bit_src + TRAMPOLINE_32BIT_CODE_SIZE 588 589 .text 590 SYM_FUNC_START_LOCAL_NOALIGN(.Lno_longmode) 591 /* This isn't an x86-64 CPU, so hang intentionally, we cannot continue */ 592 1: 593 hlt 594 jmp 1b 595 SYM_FUNC_END(.Lno_longmode) 596 597 .globl verify_cpu 598 #include "../../kernel/verify_cpu.S" 599 600 .data 601 SYM_DATA_START_LOCAL(gdt64) 602 .word gdt_end - gdt - 1 603 .quad gdt - gdt64 604 SYM_DATA_END(gdt64) 605 .balign 8 606 SYM_DATA_START_LOCAL(gdt) 607 .word gdt_end - gdt - 1 608 .long 0 609 .word 0 610 .quad 0x00cf9a000000ffff /* __KERNEL32_CS */ 611 .quad 0x00af9a000000ffff /* __KERNEL_CS */ 612 .quad 0x00cf92000000ffff /* __KERNEL_DS */ 613 .quad 0x0080890000000000 /* TS descriptor */ 614 .quad 0x0000000000000000 /* TS continued */ 615 SYM_DATA_END_LABEL(gdt, SYM_L_LOCAL, gdt_end) 616 617 SYM_DATA_START(boot_idt_desc) 618 .word boot_idt_end - boot_idt - 1 619 .quad 0 620 SYM_DATA_END(boot_idt_desc) 621 .balign 8 622 SYM_DATA_START(boot_idt) 623 .rept BOOT_IDT_ENTRIES 624 .quad 0 625 .quad 0 626 .endr 627 SYM_DATA_END_LABEL(boot_idt, SYM_L_GLOBAL, boot_idt_end) 628 629 /* 630 * Stack and heap for uncompression 631 */ 632 .bss 633 .balign 4 634 SYM_DATA_START_LOCAL(boot_stack) 635 .fill BOOT_STACK_SIZE, 1, 0 636 .balign 16 637 SYM_DATA_END_LABEL(boot_stack, SYM_L_LOCAL, boot_stack_end) 638 639 /* 640 * Space for page tables (not in .bss so not zeroed) 641 */ 642 .section ".pgtable","aw",@nobits 643 .balign 4096 644 SYM_DATA_LOCAL(pgtable, .fill BOOT_PGT_SIZE, 1, 0) 645 646 /* 647 * The page table is going to be used instead of page table in the trampoline 648 * memory. 649 */ 650 SYM_DATA_LOCAL(top_pgtable, .fill PAGE_SIZE, 1, 0)
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