1/* SPDX-License-Identifier: GPL-2.0 */ 2/* 3 * linux/arch/x86_64/entry.S 4 * 5 * Copyright (C) 1991, 1992 Linus Torvalds 6 * Copyright (C) 2000, 2001, 2002 Andi Kleen SuSE Labs 7 * Copyright (C) 2000 Pavel Machek <pavel@suse.cz> 8 * 9 * entry.S contains the system-call and fault low-level handling routines. 10 * 11 * Some of this is documented in Documentation/x86/entry_64.txt 12 * 13 * A note on terminology: 14 * - iret frame: Architecture defined interrupt frame from SS to RIP 15 * at the top of the kernel process stack. 16 * 17 * Some macro usage: 18 * - ENTRY/END: Define functions in the symbol table. 19 * - TRACE_IRQ_*: Trace hardirq state for lock debugging. 20 * - idtentry: Define exception entry points. 21 */ 22#include <linux/linkage.h> 23#include <asm/segment.h> 24#include <asm/cache.h> 25#include <asm/errno.h> 26#include <asm/asm-offsets.h> 27#include <asm/msr.h> 28#include <asm/unistd.h> 29#include <asm/thread_info.h> 30#include <asm/hw_irq.h> 31#include <asm/page_types.h> 32#include <asm/irqflags.h> 33#include <asm/paravirt.h> 34#include <asm/percpu.h> 35#include <asm/asm.h> 36#include <asm/smap.h> 37#include <asm/pgtable_types.h> 38#include <asm/export.h> 39#include <asm/frame.h> 40#include <asm/nospec-branch.h> 41#include <linux/err.h> 42 43#include "calling.h" 44 45.code64 46.section .entry.text, "ax" 47 48#ifdef CONFIG_PARAVIRT 49ENTRY(native_usergs_sysret64) 50 UNWIND_HINT_EMPTY 51 swapgs 52 sysretq 53END(native_usergs_sysret64) 54#endif /* CONFIG_PARAVIRT */ 55 56.macro TRACE_IRQS_FLAGS flags:req 57#ifdef CONFIG_TRACE_IRQFLAGS 58 bt $9, \flags /* interrupts off? */ 59 jnc 1f 60 TRACE_IRQS_ON 611: 62#endif 63.endm 64 65.macro TRACE_IRQS_IRETQ 66 TRACE_IRQS_FLAGS EFLAGS(%rsp) 67.endm 68 69/* 70 * When dynamic function tracer is enabled it will add a breakpoint 71 * to all locations that it is about to modify, sync CPUs, update 72 * all the code, sync CPUs, then remove the breakpoints. In this time 73 * if lockdep is enabled, it might jump back into the debug handler 74 * outside the updating of the IST protection. (TRACE_IRQS_ON/OFF). 75 * 76 * We need to change the IDT table before calling TRACE_IRQS_ON/OFF to 77 * make sure the stack pointer does not get reset back to the top 78 * of the debug stack, and instead just reuses the current stack. 79 */ 80#if defined(CONFIG_DYNAMIC_FTRACE) && defined(CONFIG_TRACE_IRQFLAGS) 81 82.macro TRACE_IRQS_OFF_DEBUG 83 call debug_stack_set_zero 84 TRACE_IRQS_OFF 85 call debug_stack_reset 86.endm 87 88.macro TRACE_IRQS_ON_DEBUG 89 call debug_stack_set_zero 90 TRACE_IRQS_ON 91 call debug_stack_reset 92.endm 93 94.macro TRACE_IRQS_IRETQ_DEBUG 95 bt $9, EFLAGS(%rsp) /* interrupts off? */ 96 jnc 1f 97 TRACE_IRQS_ON_DEBUG 981: 99.endm 100 101#else 102# define TRACE_IRQS_OFF_DEBUG TRACE_IRQS_OFF 103# define TRACE_IRQS_ON_DEBUG TRACE_IRQS_ON 104# define TRACE_IRQS_IRETQ_DEBUG TRACE_IRQS_IRETQ 105#endif 106 107/* 108 * 64-bit SYSCALL instruction entry. Up to 6 arguments in registers. 109 * 110 * This is the only entry point used for 64-bit system calls. The 111 * hardware interface is reasonably well designed and the register to 112 * argument mapping Linux uses fits well with the registers that are 113 * available when SYSCALL is used. 114 * 115 * SYSCALL instructions can be found inlined in libc implementations as 116 * well as some other programs and libraries. There are also a handful 117 * of SYSCALL instructions in the vDSO used, for example, as a 118 * clock_gettimeofday fallback. 119 * 120 * 64-bit SYSCALL saves rip to rcx, clears rflags.RF, then saves rflags to r11, 121 * then loads new ss, cs, and rip from previously programmed MSRs. 122 * rflags gets masked by a value from another MSR (so CLD and CLAC 123 * are not needed). SYSCALL does not save anything on the stack 124 * and does not change rsp. 125 * 126 * Registers on entry: 127 * rax system call number 128 * rcx return address 129 * r11 saved rflags (note: r11 is callee-clobbered register in C ABI) 130 * rdi arg0 131 * rsi arg1 132 * rdx arg2 133 * r10 arg3 (needs to be moved to rcx to conform to C ABI) 134 * r8 arg4 135 * r9 arg5 136 * (note: r12-r15, rbp, rbx are callee-preserved in C ABI) 137 * 138 * Only called from user space. 139 * 140 * When user can change pt_regs->foo always force IRET. That is because 141 * it deals with uncanonical addresses better. SYSRET has trouble 142 * with them due to bugs in both AMD and Intel CPUs. 143 */ 144 145 .pushsection .entry_trampoline, "ax" 146 147/* 148 * The code in here gets remapped into cpu_entry_area's trampoline. This means 149 * that the assembler and linker have the wrong idea as to where this code 150 * lives (and, in fact, it's mapped more than once, so it's not even at a 151 * fixed address). So we can't reference any symbols outside the entry 152 * trampoline and expect it to work. 153 * 154 * Instead, we carefully abuse %rip-relative addressing. 155 * _entry_trampoline(%rip) refers to the start of the remapped) entry 156 * trampoline. We can thus find cpu_entry_area with this macro: 157 */ 158 159#define CPU_ENTRY_AREA \ 160 _entry_trampoline - CPU_ENTRY_AREA_entry_trampoline(%rip) 161 162/* The top word of the SYSENTER stack is hot and is usable as scratch space. */ 163#define RSP_SCRATCH CPU_ENTRY_AREA_entry_stack + \ 164 SIZEOF_entry_stack - 8 + CPU_ENTRY_AREA 165 166ENTRY(entry_SYSCALL_64_trampoline) 167 UNWIND_HINT_EMPTY 168 swapgs 169 170 /* Stash the user RSP. */ 171 movq %rsp, RSP_SCRATCH 172 173 /* Note: using %rsp as a scratch reg. */ 174 SWITCH_TO_KERNEL_CR3 scratch_reg=%rsp 175 176 /* Load the top of the task stack into RSP */ 177 movq CPU_ENTRY_AREA_tss + TSS_sp1 + CPU_ENTRY_AREA, %rsp 178 179 /* Start building the simulated IRET frame. */ 180 pushq $__USER_DS /* pt_regs->ss */ 181 pushq RSP_SCRATCH /* pt_regs->sp */ 182 pushq %r11 /* pt_regs->flags */ 183 pushq $__USER_CS /* pt_regs->cs */ 184 pushq %rcx /* pt_regs->ip */ 185 186 /* 187 * x86 lacks a near absolute jump, and we can't jump to the real 188 * entry text with a relative jump. We could push the target 189 * address and then use retq, but this destroys the pipeline on 190 * many CPUs (wasting over 20 cycles on Sandy Bridge). Instead, 191 * spill RDI and restore it in a second-stage trampoline. 192 */ 193 pushq %rdi 194 movq $entry_SYSCALL_64_stage2, %rdi 195 JMP_NOSPEC %rdi 196END(entry_SYSCALL_64_trampoline) 197 198 .popsection 199 200ENTRY(entry_SYSCALL_64_stage2) 201 UNWIND_HINT_EMPTY 202 popq %rdi 203 jmp entry_SYSCALL_64_after_hwframe 204END(entry_SYSCALL_64_stage2) 205 206ENTRY(entry_SYSCALL_64) 207 UNWIND_HINT_EMPTY 208 /* 209 * Interrupts are off on entry. 210 * We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON, 211 * it is too small to ever cause noticeable irq latency. 212 */ 213 214 swapgs 215 /* 216 * This path is not taken when PAGE_TABLE_ISOLATION is disabled so it 217 * is not required to switch CR3. 218 */ 219 movq %rsp, PER_CPU_VAR(rsp_scratch) 220 movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp 221 222 /* Construct struct pt_regs on stack */ 223 pushq $__USER_DS /* pt_regs->ss */ 224 pushq PER_CPU_VAR(rsp_scratch) /* pt_regs->sp */ 225 pushq %r11 /* pt_regs->flags */ 226 pushq $__USER_CS /* pt_regs->cs */ 227 pushq %rcx /* pt_regs->ip */ 228GLOBAL(entry_SYSCALL_64_after_hwframe) 229 pushq %rax /* pt_regs->orig_ax */ 230 pushq %rdi /* pt_regs->di */ 231 pushq %rsi /* pt_regs->si */ 232 pushq %rdx /* pt_regs->dx */ 233 pushq %rcx /* pt_regs->cx */ 234 pushq $-ENOSYS /* pt_regs->ax */ 235 pushq %r8 /* pt_regs->r8 */ 236 pushq %r9 /* pt_regs->r9 */ 237 pushq %r10 /* pt_regs->r10 */ 238 pushq %r11 /* pt_regs->r11 */ 239 pushq %rbx /* pt_regs->rbx */ 240 pushq %rbp /* pt_regs->rbp */ 241 pushq %r12 /* pt_regs->r12 */ 242 pushq %r13 /* pt_regs->r13 */ 243 pushq %r14 /* pt_regs->r14 */ 244 pushq %r15 /* pt_regs->r15 */ 245 UNWIND_HINT_REGS 246 247 TRACE_IRQS_OFF 248 249 /* IRQs are off. */ 250 movq %rsp, %rdi 251 call do_syscall_64 /* returns with IRQs disabled */ 252 253 TRACE_IRQS_IRETQ /* we're about to change IF */ 254 255 /* 256 * Try to use SYSRET instead of IRET if we're returning to 257 * a completely clean 64-bit userspace context. If we're not, 258 * go to the slow exit path. 259 */ 260 movq RCX(%rsp), %rcx 261 movq RIP(%rsp), %r11 262 263 cmpq %rcx, %r11 /* SYSRET requires RCX == RIP */ 264 jne swapgs_restore_regs_and_return_to_usermode 265 266 /* 267 * On Intel CPUs, SYSRET with non-canonical RCX/RIP will #GP 268 * in kernel space. This essentially lets the user take over 269 * the kernel, since userspace controls RSP. 270 * 271 * If width of "canonical tail" ever becomes variable, this will need 272 * to be updated to remain correct on both old and new CPUs. 273 * 274 * Change top bits to match most significant bit (47th or 56th bit 275 * depending on paging mode) in the address. 276 */ 277 shl $(64 - (__VIRTUAL_MASK_SHIFT+1)), %rcx 278 sar $(64 - (__VIRTUAL_MASK_SHIFT+1)), %rcx 279 280 /* If this changed %rcx, it was not canonical */ 281 cmpq %rcx, %r11 282 jne swapgs_restore_regs_and_return_to_usermode 283 284 cmpq $__USER_CS, CS(%rsp) /* CS must match SYSRET */ 285 jne swapgs_restore_regs_and_return_to_usermode 286 287 movq R11(%rsp), %r11 288 cmpq %r11, EFLAGS(%rsp) /* R11 == RFLAGS */ 289 jne swapgs_restore_regs_and_return_to_usermode 290 291 /* 292 * SYSCALL clears RF when it saves RFLAGS in R11 and SYSRET cannot 293 * restore RF properly. If the slowpath sets it for whatever reason, we 294 * need to restore it correctly. 295 * 296 * SYSRET can restore TF, but unlike IRET, restoring TF results in a 297 * trap from userspace immediately after SYSRET. This would cause an 298 * infinite loop whenever #DB happens with register state that satisfies 299 * the opportunistic SYSRET conditions. For example, single-stepping 300 * this user code: 301 * 302 * movq $stuck_here, %rcx 303 * pushfq 304 * popq %r11 305 * stuck_here: 306 * 307 * would never get past 'stuck_here'. 308 */ 309 testq $(X86_EFLAGS_RF|X86_EFLAGS_TF), %r11 310 jnz swapgs_restore_regs_and_return_to_usermode 311 312 /* nothing to check for RSP */ 313 314 cmpq $__USER_DS, SS(%rsp) /* SS must match SYSRET */ 315 jne swapgs_restore_regs_and_return_to_usermode 316 317 /* 318 * We win! This label is here just for ease of understanding 319 * perf profiles. Nothing jumps here. 320 */ 321syscall_return_via_sysret: 322 /* rcx and r11 are already restored (see code above) */ 323 UNWIND_HINT_EMPTY 324 POP_EXTRA_REGS 325 popq %rsi /* skip r11 */ 326 popq %r10 327 popq %r9 328 popq %r8 329 popq %rax 330 popq %rsi /* skip rcx */ 331 popq %rdx 332 popq %rsi 333 334 /* 335 * Now all regs are restored except RSP and RDI. 336 * Save old stack pointer and switch to trampoline stack. 337 */ 338 movq %rsp, %rdi 339 movq PER_CPU_VAR(cpu_tss_rw + TSS_sp0), %rsp 340 341 pushq RSP-RDI(%rdi) /* RSP */ 342 pushq (%rdi) /* RDI */ 343 344 /* 345 * We are on the trampoline stack. All regs except RDI are live. 346 * We can do future final exit work right here. 347 */ 348 SWITCH_TO_USER_CR3_STACK scratch_reg=%rdi 349 350 popq %rdi 351 popq %rsp 352 USERGS_SYSRET64 353END(entry_SYSCALL_64) 354 355/* 356 * %rdi: prev task 357 * %rsi: next task 358 */ 359ENTRY(__switch_to_asm) 360 UNWIND_HINT_FUNC 361 /* 362 * Save callee-saved registers 363 * This must match the order in inactive_task_frame 364 */ 365 pushq %rbp 366 pushq %rbx 367 pushq %r12 368 pushq %r13 369 pushq %r14 370 pushq %r15 371 372 /* switch stack */ 373 movq %rsp, TASK_threadsp(%rdi) 374 movq TASK_threadsp(%rsi), %rsp 375 376#ifdef CONFIG_CC_STACKPROTECTOR 377 movq TASK_stack_canary(%rsi), %rbx 378 movq %rbx, PER_CPU_VAR(irq_stack_union)+stack_canary_offset 379#endif 380 381#ifdef CONFIG_RETPOLINE 382 /* 383 * When switching from a shallower to a deeper call stack 384 * the RSB may either underflow or use entries populated 385 * with userspace addresses. On CPUs where those concerns 386 * exist, overwrite the RSB with entries which capture 387 * speculative execution to prevent attack. 388 */ 389 /* Clobbers %rbx */ 390 FILL_RETURN_BUFFER RSB_CLEAR_LOOPS, X86_FEATURE_RSB_CTXSW 391#endif 392 393 /* restore callee-saved registers */ 394 popq %r15 395 popq %r14 396 popq %r13 397 popq %r12 398 popq %rbx 399 popq %rbp 400 401 jmp __switch_to 402END(__switch_to_asm) 403 404/* 405 * A newly forked process directly context switches into this address. 406 * 407 * rax: prev task we switched from 408 * rbx: kernel thread func (NULL for user thread) 409 * r12: kernel thread arg 410 */ 411ENTRY(ret_from_fork) 412 UNWIND_HINT_EMPTY 413 movq %rax, %rdi 414 call schedule_tail /* rdi: 'prev' task parameter */ 415 416 testq %rbx, %rbx /* from kernel_thread? */ 417 jnz 1f /* kernel threads are uncommon */ 418 4192: 420 UNWIND_HINT_REGS 421 movq %rsp, %rdi 422 call syscall_return_slowpath /* returns with IRQs disabled */ 423 TRACE_IRQS_ON /* user mode is traced as IRQS on */ 424 jmp swapgs_restore_regs_and_return_to_usermode 425 4261: 427 /* kernel thread */ 428 movq %r12, %rdi 429 CALL_NOSPEC %rbx 430 /* 431 * A kernel thread is allowed to return here after successfully 432 * calling do_execve(). Exit to userspace to complete the execve() 433 * syscall. 434 */ 435 movq $0, RAX(%rsp) 436 jmp 2b 437END(ret_from_fork) 438 439/* 440 * Build the entry stubs with some assembler magic. 441 * We pack 1 stub into every 8-byte block. 442 */ 443 .align 8 444ENTRY(irq_entries_start) 445 vector=FIRST_EXTERNAL_VECTOR 446 .rept (FIRST_SYSTEM_VECTOR - FIRST_EXTERNAL_VECTOR) 447 UNWIND_HINT_IRET_REGS 448 pushq $(~vector+0x80) /* Note: always in signed byte range */ 449 jmp common_interrupt 450 .align 8 451 vector=vector+1 452 .endr 453END(irq_entries_start) 454 455.macro DEBUG_ENTRY_ASSERT_IRQS_OFF 456#ifdef CONFIG_DEBUG_ENTRY 457 pushq %rax 458 SAVE_FLAGS(CLBR_RAX) 459 testl $X86_EFLAGS_IF, %eax 460 jz .Lokay_\@ 461 ud2 462.Lokay_\@: 463 popq %rax 464#endif 465.endm 466 467/* 468 * Enters the IRQ stack if we're not already using it. NMI-safe. Clobbers 469 * flags and puts old RSP into old_rsp, and leaves all other GPRs alone. 470 * Requires kernel GSBASE. 471 * 472 * The invariant is that, if irq_count != -1, then the IRQ stack is in use. 473 */ 474.macro ENTER_IRQ_STACK regs=1 old_rsp 475 DEBUG_ENTRY_ASSERT_IRQS_OFF 476 movq %rsp, \old_rsp 477 478 .if \regs 479 UNWIND_HINT_REGS base=\old_rsp 480 .endif 481 482 incl PER_CPU_VAR(irq_count) 483 jnz .Lirq_stack_push_old_rsp_\@ 484 485 /* 486 * Right now, if we just incremented irq_count to zero, we've 487 * claimed the IRQ stack but we haven't switched to it yet. 488 * 489 * If anything is added that can interrupt us here without using IST, 490 * it must be *extremely* careful to limit its stack usage. This 491 * could include kprobes and a hypothetical future IST-less #DB 492 * handler. 493 * 494 * The OOPS unwinder relies on the word at the top of the IRQ 495 * stack linking back to the previous RSP for the entire time we're 496 * on the IRQ stack. For this to work reliably, we need to write 497 * it before we actually move ourselves to the IRQ stack. 498 */ 499 500 movq \old_rsp, PER_CPU_VAR(irq_stack_union + IRQ_STACK_SIZE - 8) 501 movq PER_CPU_VAR(irq_stack_ptr), %rsp 502 503#ifdef CONFIG_DEBUG_ENTRY 504 /* 505 * If the first movq above becomes wrong due to IRQ stack layout 506 * changes, the only way we'll notice is if we try to unwind right 507 * here. Assert that we set up the stack right to catch this type 508 * of bug quickly. 509 */ 510 cmpq -8(%rsp), \old_rsp 511 je .Lirq_stack_okay\@ 512 ud2 513 .Lirq_stack_okay\@: 514#endif 515 516.Lirq_stack_push_old_rsp_\@: 517 pushq \old_rsp 518 519 .if \regs 520 UNWIND_HINT_REGS indirect=1 521 .endif 522.endm 523 524/* 525 * Undoes ENTER_IRQ_STACK. 526 */ 527.macro LEAVE_IRQ_STACK regs=1 528 DEBUG_ENTRY_ASSERT_IRQS_OFF 529 /* We need to be off the IRQ stack before decrementing irq_count. */ 530 popq %rsp 531 532 .if \regs 533 UNWIND_HINT_REGS 534 .endif 535 536 /* 537 * As in ENTER_IRQ_STACK, irq_count == 0, we are still claiming 538 * the irq stack but we're not on it. 539 */ 540 541 decl PER_CPU_VAR(irq_count) 542.endm 543 544/* 545 * Interrupt entry/exit. 546 * 547 * Interrupt entry points save only callee clobbered registers in fast path. 548 * 549 * Entry runs with interrupts off. 550 */ 551 552/* 0(%rsp): ~(interrupt number) */ 553 .macro interrupt func 554 cld 555 556 testb $3, CS-ORIG_RAX(%rsp) 557 jz 1f 558 SWAPGS 559 call switch_to_thread_stack 5601: 561 562 ALLOC_PT_GPREGS_ON_STACK 563 SAVE_C_REGS 564 SAVE_EXTRA_REGS 565 ENCODE_FRAME_POINTER 566 567 testb $3, CS(%rsp) 568 jz 1f 569 570 /* 571 * IRQ from user mode. 572 * 573 * We need to tell lockdep that IRQs are off. We can't do this until 574 * we fix gsbase, and we should do it before enter_from_user_mode 575 * (which can take locks). Since TRACE_IRQS_OFF idempotent, 576 * the simplest way to handle it is to just call it twice if 577 * we enter from user mode. There's no reason to optimize this since 578 * TRACE_IRQS_OFF is a no-op if lockdep is off. 579 */ 580 TRACE_IRQS_OFF 581 582 CALL_enter_from_user_mode 583 5841: 585 ENTER_IRQ_STACK old_rsp=%rdi 586 /* We entered an interrupt context - irqs are off: */ 587 TRACE_IRQS_OFF 588 589 call \func /* rdi points to pt_regs */ 590 .endm 591 592 /* 593 * The interrupt stubs push (~vector+0x80) onto the stack and 594 * then jump to common_interrupt. 595 */ 596 .p2align CONFIG_X86_L1_CACHE_SHIFT 597common_interrupt: 598 ASM_CLAC 599 addq $-0x80, (%rsp) /* Adjust vector to [-256, -1] range */ 600 interrupt do_IRQ 601 /* 0(%rsp): old RSP */ 602ret_from_intr: 603 DISABLE_INTERRUPTS(CLBR_ANY) 604 TRACE_IRQS_OFF 605 606 LEAVE_IRQ_STACK 607 608 testb $3, CS(%rsp) 609 jz retint_kernel 610 611 /* Interrupt came from user space */ 612GLOBAL(retint_user) 613 mov %rsp,%rdi 614 call prepare_exit_to_usermode 615 TRACE_IRQS_IRETQ 616 617GLOBAL(swapgs_restore_regs_and_return_to_usermode) 618#ifdef CONFIG_DEBUG_ENTRY 619 /* Assert that pt_regs indicates user mode. */ 620 testb $3, CS(%rsp) 621 jnz 1f 622 ud2 6231: 624#endif 625 POP_EXTRA_REGS 626 popq %r11 627 popq %r10 628 popq %r9 629 popq %r8 630 popq %rax 631 popq %rcx 632 popq %rdx 633 popq %rsi 634 635 /* 636 * The stack is now user RDI, orig_ax, RIP, CS, EFLAGS, RSP, SS. 637 * Save old stack pointer and switch to trampoline stack. 638 */ 639 movq %rsp, %rdi 640 movq PER_CPU_VAR(cpu_tss_rw + TSS_sp0), %rsp 641 642 /* Copy the IRET frame to the trampoline stack. */ 643 pushq 6*8(%rdi) /* SS */ 644 pushq 5*8(%rdi) /* RSP */ 645 pushq 4*8(%rdi) /* EFLAGS */ 646 pushq 3*8(%rdi) /* CS */ 647 pushq 2*8(%rdi) /* RIP */ 648 649 /* Push user RDI on the trampoline stack. */ 650 pushq (%rdi) 651 652 /* 653 * We are on the trampoline stack. All regs except RDI are live. 654 * We can do future final exit work right here. 655 */ 656 657 SWITCH_TO_USER_CR3_STACK scratch_reg=%rdi 658 659 /* Restore RDI. */ 660 popq %rdi 661 SWAPGS 662 INTERRUPT_RETURN 663 664 665/* Returning to kernel space */ 666retint_kernel: 667#ifdef CONFIG_PREEMPT 668 /* Interrupts are off */ 669 /* Check if we need preemption */ 670 bt $9, EFLAGS(%rsp) /* were interrupts off? */ 671 jnc 1f 6720: cmpl $0, PER_CPU_VAR(__preempt_count) 673 jnz 1f 674 call preempt_schedule_irq 675 jmp 0b 6761: 677#endif 678 /* 679 * The iretq could re-enable interrupts: 680 */ 681 TRACE_IRQS_IRETQ 682 683GLOBAL(restore_regs_and_return_to_kernel) 684#ifdef CONFIG_DEBUG_ENTRY 685 /* Assert that pt_regs indicates kernel mode. */ 686 testb $3, CS(%rsp) 687 jz 1f 688 ud2 6891: 690#endif 691 POP_EXTRA_REGS 692 POP_C_REGS 693 addq $8, %rsp /* skip regs->orig_ax */ 694 INTERRUPT_RETURN 695 696ENTRY(native_iret) 697 UNWIND_HINT_IRET_REGS 698 /* 699 * Are we returning to a stack segment from the LDT? Note: in 700 * 64-bit mode SS:RSP on the exception stack is always valid. 701 */ 702#ifdef CONFIG_X86_ESPFIX64 703 testb $4, (SS-RIP)(%rsp) 704 jnz native_irq_return_ldt 705#endif 706 707.global native_irq_return_iret 708native_irq_return_iret: 709 /* 710 * This may fault. Non-paranoid faults on return to userspace are 711 * handled by fixup_bad_iret. These include #SS, #GP, and #NP. 712 * Double-faults due to espfix64 are handled in do_double_fault. 713 * Other faults here are fatal. 714 */ 715 iretq 716 717#ifdef CONFIG_X86_ESPFIX64 718native_irq_return_ldt: 719 /* 720 * We are running with user GSBASE. All GPRs contain their user 721 * values. We have a percpu ESPFIX stack that is eight slots 722 * long (see ESPFIX_STACK_SIZE). espfix_waddr points to the bottom 723 * of the ESPFIX stack. 724 * 725 * We clobber RAX and RDI in this code. We stash RDI on the 726 * normal stack and RAX on the ESPFIX stack. 727 * 728 * The ESPFIX stack layout we set up looks like this: 729 * 730 * --- top of ESPFIX stack --- 731 * SS 732 * RSP 733 * RFLAGS 734 * CS 735 * RIP <-- RSP points here when we're done 736 * RAX <-- espfix_waddr points here 737 * --- bottom of ESPFIX stack --- 738 */ 739 740 pushq %rdi /* Stash user RDI */ 741 SWAPGS /* to kernel GS */ 742 SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi /* to kernel CR3 */ 743 744 movq PER_CPU_VAR(espfix_waddr), %rdi 745 movq %rax, (0*8)(%rdi) /* user RAX */ 746 movq (1*8)(%rsp), %rax /* user RIP */ 747 movq %rax, (1*8)(%rdi) 748 movq (2*8)(%rsp), %rax /* user CS */ 749 movq %rax, (2*8)(%rdi) 750 movq (3*8)(%rsp), %rax /* user RFLAGS */ 751 movq %rax, (3*8)(%rdi) 752 movq (5*8)(%rsp), %rax /* user SS */ 753 movq %rax, (5*8)(%rdi) 754 movq (4*8)(%rsp), %rax /* user RSP */ 755 movq %rax, (4*8)(%rdi) 756 /* Now RAX == RSP. */ 757 758 andl $0xffff0000, %eax /* RAX = (RSP & 0xffff0000) */ 759 760 /* 761 * espfix_stack[31:16] == 0. The page tables are set up such that 762 * (espfix_stack | (X & 0xffff0000)) points to a read-only alias of 763 * espfix_waddr for any X. That is, there are 65536 RO aliases of 764 * the same page. Set up RSP so that RSP[31:16] contains the 765 * respective 16 bits of the /userspace/ RSP and RSP nonetheless 766 * still points to an RO alias of the ESPFIX stack. 767 */ 768 orq PER_CPU_VAR(espfix_stack), %rax 769 770 SWITCH_TO_USER_CR3_STACK scratch_reg=%rdi 771 SWAPGS /* to user GS */ 772 popq %rdi /* Restore user RDI */ 773 774 movq %rax, %rsp 775 UNWIND_HINT_IRET_REGS offset=8 776 777 /* 778 * At this point, we cannot write to the stack any more, but we can 779 * still read. 780 */ 781 popq %rax /* Restore user RAX */ 782 783 /* 784 * RSP now points to an ordinary IRET frame, except that the page 785 * is read-only and RSP[31:16] are preloaded with the userspace 786 * values. We can now IRET back to userspace. 787 */ 788 jmp native_irq_return_iret 789#endif 790END(common_interrupt) 791 792/* 793 * APIC interrupts. 794 */ 795.macro apicinterrupt3 num sym do_sym 796ENTRY(\sym) 797 UNWIND_HINT_IRET_REGS 798 ASM_CLAC 799 pushq $~(\num) 800.Lcommon_\sym: 801 interrupt \do_sym 802 jmp ret_from_intr 803END(\sym) 804.endm 805 806/* Make sure APIC interrupt handlers end up in the irqentry section: */ 807#define PUSH_SECTION_IRQENTRY .pushsection .irqentry.text, "ax" 808#define POP_SECTION_IRQENTRY .popsection 809 810.macro apicinterrupt num sym do_sym 811PUSH_SECTION_IRQENTRY 812apicinterrupt3 \num \sym \do_sym 813POP_SECTION_IRQENTRY 814.endm 815 816#ifdef CONFIG_SMP 817apicinterrupt3 IRQ_MOVE_CLEANUP_VECTOR irq_move_cleanup_interrupt smp_irq_move_cleanup_interrupt 818apicinterrupt3 REBOOT_VECTOR reboot_interrupt smp_reboot_interrupt 819#endif 820 821#ifdef CONFIG_X86_UV 822apicinterrupt3 UV_BAU_MESSAGE uv_bau_message_intr1 uv_bau_message_interrupt 823#endif 824 825apicinterrupt LOCAL_TIMER_VECTOR apic_timer_interrupt smp_apic_timer_interrupt 826apicinterrupt X86_PLATFORM_IPI_VECTOR x86_platform_ipi smp_x86_platform_ipi 827 828#ifdef CONFIG_HAVE_KVM 829apicinterrupt3 POSTED_INTR_VECTOR kvm_posted_intr_ipi smp_kvm_posted_intr_ipi 830apicinterrupt3 POSTED_INTR_WAKEUP_VECTOR kvm_posted_intr_wakeup_ipi smp_kvm_posted_intr_wakeup_ipi 831apicinterrupt3 POSTED_INTR_NESTED_VECTOR kvm_posted_intr_nested_ipi smp_kvm_posted_intr_nested_ipi 832#endif 833 834#ifdef CONFIG_X86_MCE_THRESHOLD 835apicinterrupt THRESHOLD_APIC_VECTOR threshold_interrupt smp_threshold_interrupt 836#endif 837 838#ifdef CONFIG_X86_MCE_AMD 839apicinterrupt DEFERRED_ERROR_VECTOR deferred_error_interrupt smp_deferred_error_interrupt 840#endif 841 842#ifdef CONFIG_X86_THERMAL_VECTOR 843apicinterrupt THERMAL_APIC_VECTOR thermal_interrupt smp_thermal_interrupt 844#endif 845 846#ifdef CONFIG_SMP 847apicinterrupt CALL_FUNCTION_SINGLE_VECTOR call_function_single_interrupt smp_call_function_single_interrupt 848apicinterrupt CALL_FUNCTION_VECTOR call_function_interrupt smp_call_function_interrupt 849apicinterrupt RESCHEDULE_VECTOR reschedule_interrupt smp_reschedule_interrupt 850#endif 851 852apicinterrupt ERROR_APIC_VECTOR error_interrupt smp_error_interrupt 853apicinterrupt SPURIOUS_APIC_VECTOR spurious_interrupt smp_spurious_interrupt 854 855#ifdef CONFIG_IRQ_WORK 856apicinterrupt IRQ_WORK_VECTOR irq_work_interrupt smp_irq_work_interrupt 857#endif 858 859/* 860 * Exception entry points. 861 */ 862#define CPU_TSS_IST(x) PER_CPU_VAR(cpu_tss_rw) + (TSS_ist + ((x) - 1) * 8) 863 864/* 865 * Switch to the thread stack. This is called with the IRET frame and 866 * orig_ax on the stack. (That is, RDI..R12 are not on the stack and 867 * space has not been allocated for them.) 868 */ 869ENTRY(switch_to_thread_stack) 870 UNWIND_HINT_FUNC 871 872 pushq %rdi 873 /* Need to switch before accessing the thread stack. */ 874 SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi 875 movq %rsp, %rdi 876 movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp 877 UNWIND_HINT sp_offset=16 sp_reg=ORC_REG_DI 878 879 pushq 7*8(%rdi) /* regs->ss */ 880 pushq 6*8(%rdi) /* regs->rsp */ 881 pushq 5*8(%rdi) /* regs->eflags */ 882 pushq 4*8(%rdi) /* regs->cs */ 883 pushq 3*8(%rdi) /* regs->ip */ 884 pushq 2*8(%rdi) /* regs->orig_ax */ 885 pushq 8(%rdi) /* return address */ 886 UNWIND_HINT_FUNC 887 888 movq (%rdi), %rdi 889 ret 890END(switch_to_thread_stack) 891 892.macro idtentry sym do_sym has_error_code:req paranoid=0 shift_ist=-1 893ENTRY(\sym) 894 UNWIND_HINT_IRET_REGS offset=\has_error_code*8 895 896 /* Sanity check */ 897 .if \shift_ist != -1 && \paranoid == 0 898 .error "using shift_ist requires paranoid=1" 899 .endif 900 901 ASM_CLAC 902 903 .if \has_error_code == 0 904 pushq $-1 /* ORIG_RAX: no syscall to restart */ 905 .endif 906 907 ALLOC_PT_GPREGS_ON_STACK 908 909 .if \paranoid < 2 910 testb $3, CS(%rsp) /* If coming from userspace, switch stacks */ 911 jnz .Lfrom_usermode_switch_stack_\@ 912 .endif 913 914 .if \paranoid 915 call paranoid_entry 916 .else 917 call error_entry 918 .endif 919 UNWIND_HINT_REGS 920 /* returned flag: ebx=0: need swapgs on exit, ebx=1: don't need it */ 921 922 .if \paranoid 923 .if \shift_ist != -1 924 TRACE_IRQS_OFF_DEBUG /* reload IDT in case of recursion */ 925 .else 926 TRACE_IRQS_OFF 927 .endif 928 .endif 929 930 movq %rsp, %rdi /* pt_regs pointer */ 931 932 .if \has_error_code 933 movq ORIG_RAX(%rsp), %rsi /* get error code */ 934 movq $-1, ORIG_RAX(%rsp) /* no syscall to restart */ 935 .else 936 xorl %esi, %esi /* no error code */ 937 .endif 938 939 .if \shift_ist != -1 940 subq $EXCEPTION_STKSZ, CPU_TSS_IST(\shift_ist) 941 .endif 942 943 call \do_sym 944 945 .if \shift_ist != -1 946 addq $EXCEPTION_STKSZ, CPU_TSS_IST(\shift_ist) 947 .endif 948 949 /* these procedures expect "no swapgs" flag in ebx */ 950 .if \paranoid 951 jmp paranoid_exit 952 .else 953 jmp error_exit 954 .endif 955 956 .if \paranoid < 2 957 /* 958 * Entry from userspace. Switch stacks and treat it 959 * as a normal entry. This means that paranoid handlers 960 * run in real process context if user_mode(regs). 961 */ 962.Lfrom_usermode_switch_stack_\@: 963 call error_entry 964 965 movq %rsp, %rdi /* pt_regs pointer */ 966 967 .if \has_error_code 968 movq ORIG_RAX(%rsp), %rsi /* get error code */ 969 movq $-1, ORIG_RAX(%rsp) /* no syscall to restart */ 970 .else 971 xorl %esi, %esi /* no error code */ 972 .endif 973 974 call \do_sym 975 976 jmp error_exit /* %ebx: no swapgs flag */ 977 .endif 978END(\sym) 979.endm 980 981idtentry divide_error do_divide_error has_error_code=0 982idtentry overflow do_overflow has_error_code=0 983idtentry bounds do_bounds has_error_code=0 984idtentry invalid_op do_invalid_op has_error_code=0 985idtentry device_not_available do_device_not_available has_error_code=0 986idtentry double_fault do_double_fault has_error_code=1 paranoid=2 987idtentry coprocessor_segment_overrun do_coprocessor_segment_overrun has_error_code=0 988idtentry invalid_TSS do_invalid_TSS has_error_code=1 989idtentry segment_not_present do_segment_not_present has_error_code=1 990idtentry spurious_interrupt_bug do_spurious_interrupt_bug has_error_code=0 991idtentry coprocessor_error do_coprocessor_error has_error_code=0 992idtentry alignment_check do_alignment_check has_error_code=1 993idtentry simd_coprocessor_error do_simd_coprocessor_error has_error_code=0 994 995 996 /* 997 * Reload gs selector with exception handling 998 * edi: new selector 999 */ 1000ENTRY(native_load_gs_index) 1001 FRAME_BEGIN 1002 pushfq 1003 DISABLE_INTERRUPTS(CLBR_ANY & ~CLBR_RDI) 1004 TRACE_IRQS_OFF 1005 SWAPGS 1006.Lgs_change: 1007 movl %edi, %gs 10082: ALTERNATIVE "", "mfence", X86_BUG_SWAPGS_FENCE 1009 SWAPGS 1010 TRACE_IRQS_FLAGS (%rsp) 1011 popfq 1012 FRAME_END 1013 ret 1014ENDPROC(native_load_gs_index) 1015EXPORT_SYMBOL(native_load_gs_index) 1016 1017 _ASM_EXTABLE(.Lgs_change, bad_gs) 1018 .section .fixup, "ax" 1019 /* running with kernelgs */ 1020bad_gs: 1021 SWAPGS /* switch back to user gs */ 1022.macro ZAP_GS 1023 /* This can't be a string because the preprocessor needs to see it. */ 1024 movl $__USER_DS, %eax 1025 movl %eax, %gs 1026.endm 1027 ALTERNATIVE "", "ZAP_GS", X86_BUG_NULL_SEG 1028 xorl %eax, %eax 1029 movl %eax, %gs 1030 jmp 2b 1031 .previous 1032 1033/* Call softirq on interrupt stack. Interrupts are off. */ 1034ENTRY(do_softirq_own_stack) 1035 pushq %rbp 1036 mov %rsp, %rbp 1037 ENTER_IRQ_STACK regs=0 old_rsp=%r11 1038 call __do_softirq 1039 LEAVE_IRQ_STACK regs=0 1040 leaveq 1041 ret 1042ENDPROC(do_softirq_own_stack) 1043 1044#ifdef CONFIG_XEN 1045idtentry hypervisor_callback xen_do_hypervisor_callback has_error_code=0 1046 1047/* 1048 * A note on the "critical region" in our callback handler. 1049 * We want to avoid stacking callback handlers due to events occurring 1050 * during handling of the last event. To do this, we keep events disabled 1051 * until we've done all processing. HOWEVER, we must enable events before 1052 * popping the stack frame (can't be done atomically) and so it would still 1053 * be possible to get enough handler activations to overflow the stack. 1054 * Although unlikely, bugs of that kind are hard to track down, so we'd 1055 * like to avoid the possibility. 1056 * So, on entry to the handler we detect whether we interrupted an 1057 * existing activation in its critical region -- if so, we pop the current 1058 * activation and restart the handler using the previous one. 1059 */ 1060ENTRY(xen_do_hypervisor_callback) /* do_hypervisor_callback(struct *pt_regs) */ 1061 1062/* 1063 * Since we don't modify %rdi, evtchn_do_upall(struct *pt_regs) will 1064 * see the correct pointer to the pt_regs 1065 */ 1066 UNWIND_HINT_FUNC 1067 movq %rdi, %rsp /* we don't return, adjust the stack frame */ 1068 UNWIND_HINT_REGS 1069 1070 ENTER_IRQ_STACK old_rsp=%r10 1071 call xen_evtchn_do_upcall 1072 LEAVE_IRQ_STACK 1073 1074#ifndef CONFIG_PREEMPT 1075 call xen_maybe_preempt_hcall 1076#endif 1077 jmp error_exit 1078END(xen_do_hypervisor_callback) 1079 1080/* 1081 * Hypervisor uses this for application faults while it executes. 1082 * We get here for two reasons: 1083 * 1. Fault while reloading DS, ES, FS or GS 1084 * 2. Fault while executing IRET 1085 * Category 1 we do not need to fix up as Xen has already reloaded all segment 1086 * registers that could be reloaded and zeroed the others. 1087 * Category 2 we fix up by killing the current process. We cannot use the 1088 * normal Linux return path in this case because if we use the IRET hypercall 1089 * to pop the stack frame we end up in an infinite loop of failsafe callbacks. 1090 * We distinguish between categories by comparing each saved segment register 1091 * with its current contents: any discrepancy means we in category 1. 1092 */ 1093ENTRY(xen_failsafe_callback) 1094 UNWIND_HINT_EMPTY 1095 movl %ds, %ecx 1096 cmpw %cx, 0x10(%rsp) 1097 jne 1f 1098 movl %es, %ecx 1099 cmpw %cx, 0x18(%rsp) 1100 jne 1f 1101 movl %fs, %ecx 1102 cmpw %cx, 0x20(%rsp) 1103 jne 1f 1104 movl %gs, %ecx 1105 cmpw %cx, 0x28(%rsp) 1106 jne 1f 1107 /* All segments match their saved values => Category 2 (Bad IRET). */ 1108 movq (%rsp), %rcx 1109 movq 8(%rsp), %r11 1110 addq $0x30, %rsp 1111 pushq $0 /* RIP */ 1112 UNWIND_HINT_IRET_REGS offset=8 1113 jmp general_protection 11141: /* Segment mismatch => Category 1 (Bad segment). Retry the IRET. */ 1115 movq (%rsp), %rcx 1116 movq 8(%rsp), %r11 1117 addq $0x30, %rsp 1118 UNWIND_HINT_IRET_REGS 1119 pushq $-1 /* orig_ax = -1 => not a system call */ 1120 ALLOC_PT_GPREGS_ON_STACK 1121 SAVE_C_REGS 1122 SAVE_EXTRA_REGS 1123 ENCODE_FRAME_POINTER 1124 jmp error_exit 1125END(xen_failsafe_callback) 1126 1127apicinterrupt3 HYPERVISOR_CALLBACK_VECTOR \ 1128 xen_hvm_callback_vector xen_evtchn_do_upcall 1129 1130#endif /* CONFIG_XEN */ 1131 1132#if IS_ENABLED(CONFIG_HYPERV) 1133apicinterrupt3 HYPERVISOR_CALLBACK_VECTOR \ 1134 hyperv_callback_vector hyperv_vector_handler 1135#endif /* CONFIG_HYPERV */ 1136 1137idtentry debug do_debug has_error_code=0 paranoid=1 shift_ist=DEBUG_STACK 1138idtentry int3 do_int3 has_error_code=0 paranoid=1 shift_ist=DEBUG_STACK 1139idtentry stack_segment do_stack_segment has_error_code=1 1140 1141#ifdef CONFIG_XEN 1142idtentry xennmi do_nmi has_error_code=0 1143idtentry xendebug do_debug has_error_code=0 1144idtentry xenint3 do_int3 has_error_code=0 1145#endif 1146 1147idtentry general_protection do_general_protection has_error_code=1 1148idtentry page_fault do_page_fault has_error_code=1 1149 1150#ifdef CONFIG_KVM_GUEST 1151idtentry async_page_fault do_async_page_fault has_error_code=1 1152#endif 1153 1154#ifdef CONFIG_X86_MCE 1155idtentry machine_check do_mce has_error_code=0 paranoid=1 1156#endif 1157 1158/* 1159 * Save all registers in pt_regs, and switch gs if needed. 1160 * Use slow, but surefire "are we in kernel?" check. 1161 * Return: ebx=0: need swapgs on exit, ebx=1: otherwise 1162 */ 1163ENTRY(paranoid_entry) 1164 UNWIND_HINT_FUNC 1165 cld 1166 SAVE_C_REGS 8 1167 SAVE_EXTRA_REGS 8 1168 ENCODE_FRAME_POINTER 8 1169 movl $1, %ebx 1170 movl $MSR_GS_BASE, %ecx 1171 rdmsr 1172 testl %edx, %edx 1173 js 1f /* negative -> in kernel */ 1174 SWAPGS 1175 xorl %ebx, %ebx 1176 11771: 1178 SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg=%rax save_reg=%r14 1179 1180 ret 1181END(paranoid_entry) 1182 1183/* 1184 * "Paranoid" exit path from exception stack. This is invoked 1185 * only on return from non-NMI IST interrupts that came 1186 * from kernel space. 1187 * 1188 * We may be returning to very strange contexts (e.g. very early 1189 * in syscall entry), so checking for preemption here would 1190 * be complicated. Fortunately, we there's no good reason 1191 * to try to handle preemption here. 1192 * 1193 * On entry, ebx is "no swapgs" flag (1: don't need swapgs, 0: need it) 1194 */ 1195ENTRY(paranoid_exit) 1196 UNWIND_HINT_REGS 1197 DISABLE_INTERRUPTS(CLBR_ANY) 1198 TRACE_IRQS_OFF_DEBUG 1199 testl %ebx, %ebx /* swapgs needed? */ 1200 jnz .Lparanoid_exit_no_swapgs 1201 TRACE_IRQS_IRETQ 1202 RESTORE_CR3 scratch_reg=%rbx save_reg=%r14 1203 SWAPGS_UNSAFE_STACK 1204 jmp .Lparanoid_exit_restore 1205.Lparanoid_exit_no_swapgs: 1206 TRACE_IRQS_IRETQ_DEBUG 1207.Lparanoid_exit_restore: 1208 jmp restore_regs_and_return_to_kernel 1209END(paranoid_exit) 1210 1211/* 1212 * Save all registers in pt_regs, and switch gs if needed. 1213 * Return: EBX=0: came from user mode; EBX=1: otherwise 1214 */ 1215ENTRY(error_entry) 1216 UNWIND_HINT_FUNC 1217 cld 1218 SAVE_C_REGS 8 1219 SAVE_EXTRA_REGS 8 1220 ENCODE_FRAME_POINTER 8 1221 xorl %ebx, %ebx 1222 testb $3, CS+8(%rsp) 1223 jz .Lerror_kernelspace 1224 1225 /* 1226 * We entered from user mode or we're pretending to have entered 1227 * from user mode due to an IRET fault. 1228 */ 1229 SWAPGS 1230 /* We have user CR3. Change to kernel CR3. */ 1231 SWITCH_TO_KERNEL_CR3 scratch_reg=%rax 1232 1233.Lerror_entry_from_usermode_after_swapgs: 1234 /* Put us onto the real thread stack. */ 1235 popq %r12 /* save return addr in %12 */ 1236 movq %rsp, %rdi /* arg0 = pt_regs pointer */ 1237 call sync_regs 1238 movq %rax, %rsp /* switch stack */ 1239 ENCODE_FRAME_POINTER 1240 pushq %r12 1241 1242 /* 1243 * We need to tell lockdep that IRQs are off. We can't do this until 1244 * we fix gsbase, and we should do it before enter_from_user_mode 1245 * (which can take locks). 1246 */ 1247 TRACE_IRQS_OFF 1248 CALL_enter_from_user_mode 1249 ret 1250 1251.Lerror_entry_done: 1252 TRACE_IRQS_OFF 1253 ret 1254 1255 /* 1256 * There are two places in the kernel that can potentially fault with 1257 * usergs. Handle them here. B stepping K8s sometimes report a 1258 * truncated RIP for IRET exceptions returning to compat mode. Check 1259 * for these here too. 1260 */ 1261.Lerror_kernelspace: 1262 incl %ebx 1263 leaq native_irq_return_iret(%rip), %rcx 1264 cmpq %rcx, RIP+8(%rsp) 1265 je .Lerror_bad_iret 1266 movl %ecx, %eax /* zero extend */ 1267 cmpq %rax, RIP+8(%rsp) 1268 je .Lbstep_iret 1269 cmpq $.Lgs_change, RIP+8(%rsp) 1270 jne .Lerror_entry_done 1271 1272 /* 1273 * hack: .Lgs_change can fail with user gsbase. If this happens, fix up 1274 * gsbase and proceed. We'll fix up the exception and land in 1275 * .Lgs_change's error handler with kernel gsbase. 1276 */ 1277 SWAPGS 1278 SWITCH_TO_KERNEL_CR3 scratch_reg=%rax 1279 jmp .Lerror_entry_done 1280 1281.Lbstep_iret: 1282 /* Fix truncated RIP */ 1283 movq %rcx, RIP+8(%rsp) 1284 /* fall through */ 1285 1286.Lerror_bad_iret: 1287 /* 1288 * We came from an IRET to user mode, so we have user 1289 * gsbase and CR3. Switch to kernel gsbase and CR3: 1290 */ 1291 SWAPGS 1292 SWITCH_TO_KERNEL_CR3 scratch_reg=%rax 1293 1294 /* 1295 * Pretend that the exception came from user mode: set up pt_regs 1296 * as if we faulted immediately after IRET and clear EBX so that 1297 * error_exit knows that we will be returning to user mode. 1298 */ 1299 mov %rsp, %rdi 1300 call fixup_bad_iret 1301 mov %rax, %rsp 1302 decl %ebx 1303 jmp .Lerror_entry_from_usermode_after_swapgs 1304END(error_entry) 1305 1306 1307/* 1308 * On entry, EBX is a "return to kernel mode" flag: 1309 * 1: already in kernel mode, don't need SWAPGS 1310 * 0: user gsbase is loaded, we need SWAPGS and standard preparation for return to usermode 1311 */ 1312ENTRY(error_exit) 1313 UNWIND_HINT_REGS 1314 DISABLE_INTERRUPTS(CLBR_ANY) 1315 TRACE_IRQS_OFF 1316 testl %ebx, %ebx 1317 jnz retint_kernel 1318 jmp retint_user 1319END(error_exit) 1320 1321/* 1322 * Runs on exception stack. Xen PV does not go through this path at all, 1323 * so we can use real assembly here. 1324 * 1325 * Registers: 1326 * %r14: Used to save/restore the CR3 of the interrupted context 1327 * when PAGE_TABLE_ISOLATION is in use. Do not clobber. 1328 */ 1329ENTRY(nmi) 1330 UNWIND_HINT_IRET_REGS 1331 1332 /* 1333 * We allow breakpoints in NMIs. If a breakpoint occurs, then 1334 * the iretq it performs will take us out of NMI context. 1335 * This means that we can have nested NMIs where the next 1336 * NMI is using the top of the stack of the previous NMI. We 1337 * can't let it execute because the nested NMI will corrupt the 1338 * stack of the previous NMI. NMI handlers are not re-entrant 1339 * anyway. 1340 * 1341 * To handle this case we do the following: 1342 * Check the a special location on the stack that contains 1343 * a variable that is set when NMIs are executing. 1344 * The interrupted task's stack is also checked to see if it 1345 * is an NMI stack. 1346 * If the variable is not set and the stack is not the NMI 1347 * stack then: 1348 * o Set the special variable on the stack 1349 * o Copy the interrupt frame into an "outermost" location on the 1350 * stack 1351 * o Copy the interrupt frame into an "iret" location on the stack 1352 * o Continue processing the NMI 1353 * If the variable is set or the previous stack is the NMI stack: 1354 * o Modify the "iret" location to jump to the repeat_nmi 1355 * o return back to the first NMI 1356 * 1357 * Now on exit of the first NMI, we first clear the stack variable 1358 * The NMI stack will tell any nested NMIs at that point that it is 1359 * nested. Then we pop the stack normally with iret, and if there was 1360 * a nested NMI that updated the copy interrupt stack frame, a 1361 * jump will be made to the repeat_nmi code that will handle the second 1362 * NMI. 1363 * 1364 * However, espfix prevents us from directly returning to userspace 1365 * with a single IRET instruction. Similarly, IRET to user mode 1366 * can fault. We therefore handle NMIs from user space like 1367 * other IST entries. 1368 */ 1369 1370 ASM_CLAC 1371 1372 /* Use %rdx as our temp variable throughout */ 1373 pushq %rdx 1374 1375 testb $3, CS-RIP+8(%rsp) 1376 jz .Lnmi_from_kernel 1377 1378 /* 1379 * NMI from user mode. We need to run on the thread stack, but we 1380 * can't go through the normal entry paths: NMIs are masked, and 1381 * we don't want to enable interrupts, because then we'll end 1382 * up in an awkward situation in which IRQs are on but NMIs 1383 * are off. 1384 * 1385 * We also must not push anything to the stack before switching 1386 * stacks lest we corrupt the "NMI executing" variable. 1387 */ 1388 1389 swapgs 1390 cld 1391 SWITCH_TO_KERNEL_CR3 scratch_reg=%rdx 1392 movq %rsp, %rdx 1393 movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp 1394 UNWIND_HINT_IRET_REGS base=%rdx offset=8 1395 pushq 5*8(%rdx) /* pt_regs->ss */ 1396 pushq 4*8(%rdx) /* pt_regs->rsp */ 1397 pushq 3*8(%rdx) /* pt_regs->flags */ 1398 pushq 2*8(%rdx) /* pt_regs->cs */ 1399 pushq 1*8(%rdx) /* pt_regs->rip */ 1400 UNWIND_HINT_IRET_REGS 1401 pushq $-1 /* pt_regs->orig_ax */ 1402 pushq %rdi /* pt_regs->di */ 1403 pushq %rsi /* pt_regs->si */ 1404 pushq (%rdx) /* pt_regs->dx */ 1405 pushq %rcx /* pt_regs->cx */ 1406 pushq %rax /* pt_regs->ax */ 1407 pushq %r8 /* pt_regs->r8 */ 1408 pushq %r9 /* pt_regs->r9 */ 1409 pushq %r10 /* pt_regs->r10 */ 1410 pushq %r11 /* pt_regs->r11 */ 1411 pushq %rbx /* pt_regs->rbx */ 1412 pushq %rbp /* pt_regs->rbp */ 1413 pushq %r12 /* pt_regs->r12 */ 1414 pushq %r13 /* pt_regs->r13 */ 1415 pushq %r14 /* pt_regs->r14 */ 1416 pushq %r15 /* pt_regs->r15 */ 1417 UNWIND_HINT_REGS 1418 ENCODE_FRAME_POINTER 1419 1420 /* 1421 * At this point we no longer need to worry about stack damage 1422 * due to nesting -- we're on the normal thread stack and we're 1423 * done with the NMI stack. 1424 */ 1425 1426 movq %rsp, %rdi 1427 movq $-1, %rsi 1428 call do_nmi 1429 1430 /* 1431 * Return back to user mode. We must *not* do the normal exit 1432 * work, because we don't want to enable interrupts. 1433 */ 1434 jmp swapgs_restore_regs_and_return_to_usermode 1435 1436.Lnmi_from_kernel: 1437 /* 1438 * Here's what our stack frame will look like: 1439 * +---------------------------------------------------------+ 1440 * | original SS | 1441 * | original Return RSP | 1442 * | original RFLAGS | 1443 * | original CS | 1444 * | original RIP | 1445 * +---------------------------------------------------------+ 1446 * | temp storage for rdx | 1447 * +---------------------------------------------------------+ 1448 * | "NMI executing" variable | 1449 * +---------------------------------------------------------+ 1450 * | iret SS } Copied from "outermost" frame | 1451 * | iret Return RSP } on each loop iteration; overwritten | 1452 * | iret RFLAGS } by a nested NMI to force another | 1453 * | iret CS } iteration if needed. | 1454 * | iret RIP } | 1455 * +---------------------------------------------------------+ 1456 * | outermost SS } initialized in first_nmi; | 1457 * | outermost Return RSP } will not be changed before | 1458 * | outermost RFLAGS } NMI processing is done. | 1459 * | outermost CS } Copied to "iret" frame on each | 1460 * | outermost RIP } iteration. | 1461 * +---------------------------------------------------------+ 1462 * | pt_regs | 1463 * +---------------------------------------------------------+ 1464 * 1465 * The "original" frame is used by hardware. Before re-enabling 1466 * NMIs, we need to be done with it, and we need to leave enough 1467 * space for the asm code here. 1468 * 1469 * We return by executing IRET while RSP points to the "iret" frame. 1470 * That will either return for real or it will loop back into NMI 1471 * processing. 1472 * 1473 * The "outermost" frame is copied to the "iret" frame on each 1474 * iteration of the loop, so each iteration starts with the "iret" 1475 * frame pointing to the final return target. 1476 */ 1477 1478 /* 1479 * Determine whether we're a nested NMI. 1480 * 1481 * If we interrupted kernel code between repeat_nmi and 1482 * end_repeat_nmi, then we are a nested NMI. We must not 1483 * modify the "iret" frame because it's being written by 1484 * the outer NMI. That's okay; the outer NMI handler is 1485 * about to about to call do_nmi anyway, so we can just 1486 * resume the outer NMI. 1487 */ 1488 1489 movq $repeat_nmi, %rdx 1490 cmpq 8(%rsp), %rdx 1491 ja 1f 1492 movq $end_repeat_nmi, %rdx 1493 cmpq 8(%rsp), %rdx 1494 ja nested_nmi_out 14951: 1496 1497 /* 1498 * Now check "NMI executing". If it's set, then we're nested. 1499 * This will not detect if we interrupted an outer NMI just 1500 * before IRET. 1501 */ 1502 cmpl $1, -8(%rsp) 1503 je nested_nmi 1504 1505 /* 1506 * Now test if the previous stack was an NMI stack. This covers 1507 * the case where we interrupt an outer NMI after it clears 1508 * "NMI executing" but before IRET. We need to be careful, though: 1509 * there is one case in which RSP could point to the NMI stack 1510 * despite there being no NMI active: naughty userspace controls 1511 * RSP at the very beginning of the SYSCALL targets. We can 1512 * pull a fast one on naughty userspace, though: we program 1513 * SYSCALL to mask DF, so userspace cannot cause DF to be set 1514 * if it controls the kernel's RSP. We set DF before we clear 1515 * "NMI executing". 1516 */ 1517 lea 6*8(%rsp), %rdx 1518 /* Compare the NMI stack (rdx) with the stack we came from (4*8(%rsp)) */ 1519 cmpq %rdx, 4*8(%rsp) 1520 /* If the stack pointer is above the NMI stack, this is a normal NMI */ 1521 ja first_nmi 1522 1523 subq $EXCEPTION_STKSZ, %rdx 1524 cmpq %rdx, 4*8(%rsp) 1525 /* If it is below the NMI stack, it is a normal NMI */ 1526 jb first_nmi 1527 1528 /* Ah, it is within the NMI stack. */ 1529 1530 testb $(X86_EFLAGS_DF >> 8), (3*8 + 1)(%rsp) 1531 jz first_nmi /* RSP was user controlled. */ 1532 1533 /* This is a nested NMI. */ 1534 1535nested_nmi: 1536 /* 1537 * Modify the "iret" frame to point to repeat_nmi, forcing another 1538 * iteration of NMI handling. 1539 */ 1540 subq $8, %rsp 1541 leaq -10*8(%rsp), %rdx 1542 pushq $__KERNEL_DS 1543 pushq %rdx 1544 pushfq 1545 pushq $__KERNEL_CS 1546 pushq $repeat_nmi 1547 1548 /* Put stack back */ 1549 addq $(6*8), %rsp 1550 1551nested_nmi_out: 1552 popq %rdx 1553 1554 /* We are returning to kernel mode, so this cannot result in a fault. */ 1555 iretq 1556 1557first_nmi: 1558 /* Restore rdx. */ 1559 movq (%rsp), %rdx 1560 1561 /* Make room for "NMI executing". */ 1562 pushq $0 1563 1564 /* Leave room for the "iret" frame */ 1565 subq $(5*8), %rsp 1566 1567 /* Copy the "original" frame to the "outermost" frame */ 1568 .rept 5 1569 pushq 11*8(%rsp) 1570 .endr 1571 UNWIND_HINT_IRET_REGS 1572 1573 /* Everything up to here is safe from nested NMIs */ 1574 1575#ifdef CONFIG_DEBUG_ENTRY 1576 /* 1577 * For ease of testing, unmask NMIs right away. Disabled by 1578 * default because IRET is very expensive. 1579 */ 1580 pushq $0 /* SS */ 1581 pushq %rsp /* RSP (minus 8 because of the previous push) */ 1582 addq $8, (%rsp) /* Fix up RSP */ 1583 pushfq /* RFLAGS */ 1584 pushq $__KERNEL_CS /* CS */ 1585 pushq $1f /* RIP */ 1586 iretq /* continues at repeat_nmi below */ 1587 UNWIND_HINT_IRET_REGS 15881: 1589#endif 1590 1591repeat_nmi: 1592 /* 1593 * If there was a nested NMI, the first NMI's iret will return 1594 * here. But NMIs are still enabled and we can take another 1595 * nested NMI. The nested NMI checks the interrupted RIP to see 1596 * if it is between repeat_nmi and end_repeat_nmi, and if so 1597 * it will just return, as we are about to repeat an NMI anyway. 1598 * This makes it safe to copy to the stack frame that a nested 1599 * NMI will update. 1600 * 1601 * RSP is pointing to "outermost RIP". gsbase is unknown, but, if 1602 * we're repeating an NMI, gsbase has the same value that it had on 1603 * the first iteration. paranoid_entry will load the kernel 1604 * gsbase if needed before we call do_nmi. "NMI executing" 1605 * is zero. 1606 */ 1607 movq $1, 10*8(%rsp) /* Set "NMI executing". */ 1608 1609 /* 1610 * Copy the "outermost" frame to the "iret" frame. NMIs that nest 1611 * here must not modify the "iret" frame while we're writing to 1612 * it or it will end up containing garbage. 1613 */ 1614 addq $(10*8), %rsp 1615 .rept 5 1616 pushq -6*8(%rsp) 1617 .endr 1618 subq $(5*8), %rsp 1619end_repeat_nmi: 1620 1621 /* 1622 * Everything below this point can be preempted by a nested NMI. 1623 * If this happens, then the inner NMI will change the "iret" 1624 * frame to point back to repeat_nmi. 1625 */ 1626 pushq $-1 /* ORIG_RAX: no syscall to restart */ 1627 ALLOC_PT_GPREGS_ON_STACK 1628 1629 /* 1630 * Use paranoid_entry to handle SWAPGS, but no need to use paranoid_exit 1631 * as we should not be calling schedule in NMI context. 1632 * Even with normal interrupts enabled. An NMI should not be 1633 * setting NEED_RESCHED or anything that normal interrupts and 1634 * exceptions might do. 1635 */ 1636 call paranoid_entry 1637 UNWIND_HINT_REGS 1638 1639 /* paranoidentry do_nmi, 0; without TRACE_IRQS_OFF */ 1640 movq %rsp, %rdi 1641 movq $-1, %rsi 1642 call do_nmi 1643 1644 RESTORE_CR3 scratch_reg=%r15 save_reg=%r14 1645 1646 testl %ebx, %ebx /* swapgs needed? */ 1647 jnz nmi_restore 1648nmi_swapgs: 1649 SWAPGS_UNSAFE_STACK 1650nmi_restore: 1651 POP_EXTRA_REGS 1652 POP_C_REGS 1653 1654 /* 1655 * Skip orig_ax and the "outermost" frame to point RSP at the "iret" 1656 * at the "iret" frame. 1657 */ 1658 addq $6*8, %rsp 1659 1660 /* 1661 * Clear "NMI executing". Set DF first so that we can easily 1662 * distinguish the remaining code between here and IRET from 1663 * the SYSCALL entry and exit paths. 1664 * 1665 * We arguably should just inspect RIP instead, but I (Andy) wrote 1666 * this code when I had the misapprehension that Xen PV supported 1667 * NMIs, and Xen PV would break that approach. 1668 */ 1669 std 1670 movq $0, 5*8(%rsp) /* clear "NMI executing" */ 1671 1672 /* 1673 * iretq reads the "iret" frame and exits the NMI stack in a 1674 * single instruction. We are returning to kernel mode, so this 1675 * cannot result in a fault. Similarly, we don't need to worry 1676 * about espfix64 on the way back to kernel mode. 1677 */ 1678 iretq 1679END(nmi) 1680 1681ENTRY(ignore_sysret) 1682 UNWIND_HINT_EMPTY 1683 mov $-ENOSYS, %eax 1684 sysret 1685END(ignore_sysret) 1686 1687ENTRY(rewind_stack_do_exit) 1688 UNWIND_HINT_FUNC 1689 /* Prevent any naive code from trying to unwind to our caller. */ 1690 xorl %ebp, %ebp 1691 1692 movq PER_CPU_VAR(cpu_current_top_of_stack), %rax 1693 leaq -PTREGS_SIZE(%rax), %rsp 1694 UNWIND_HINT_FUNC sp_offset=PTREGS_SIZE 1695 1696 call do_exit 1697END(rewind_stack_do_exit) 1698