/* * linux/arch/x86_64/entry.S * * Copyright (C) 1991, 1992 Linus Torvalds * Copyright (C) 2000, 2001, 2002 Andi Kleen SuSE Labs * Copyright (C) 2000 Pavel Machek * * entry.S contains the system-call and fault low-level handling routines. * * Some of this is documented in Documentation/x86/entry_64.txt * * A note on terminology: * - iret frame: Architecture defined interrupt frame from SS to RIP * at the top of the kernel process stack. * * Some macro usage: * - ENTRY/END: Define functions in the symbol table. * - TRACE_IRQ_*: Trace hardirq state for lock debugging. * - idtentry: Define exception entry points. */ #include #include #include #include #include "calling.h" #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include /* Avoid __ASSEMBLER__'ifying just for this. */ #include #define AUDIT_ARCH_X86_64 (EM_X86_64|__AUDIT_ARCH_64BIT|__AUDIT_ARCH_LE) #define __AUDIT_ARCH_64BIT 0x80000000 #define __AUDIT_ARCH_LE 0x40000000 .code64 .section .entry.text, "ax" #ifdef CONFIG_PARAVIRT ENTRY(native_usergs_sysret64) swapgs sysretq ENDPROC(native_usergs_sysret64) #endif /* CONFIG_PARAVIRT */ .macro TRACE_IRQS_IRETQ #ifdef CONFIG_TRACE_IRQFLAGS btl $9, EFLAGS(%rsp) /* interrupts off? */ jnc 1f TRACE_IRQS_ON 1: #endif .endm /* * When dynamic function tracer is enabled it will add a breakpoint * to all locations that it is about to modify, sync CPUs, update * all the code, sync CPUs, then remove the breakpoints. In this time * if lockdep is enabled, it might jump back into the debug handler * outside the updating of the IST protection. (TRACE_IRQS_ON/OFF). * * We need to change the IDT table before calling TRACE_IRQS_ON/OFF to * make sure the stack pointer does not get reset back to the top * of the debug stack, and instead just reuses the current stack. */ #if defined(CONFIG_DYNAMIC_FTRACE) && defined(CONFIG_TRACE_IRQFLAGS) .macro TRACE_IRQS_OFF_DEBUG call debug_stack_set_zero TRACE_IRQS_OFF call debug_stack_reset .endm .macro TRACE_IRQS_ON_DEBUG call debug_stack_set_zero TRACE_IRQS_ON call debug_stack_reset .endm .macro TRACE_IRQS_IRETQ_DEBUG btl $9, EFLAGS(%rsp) /* interrupts off? */ jnc 1f TRACE_IRQS_ON_DEBUG 1: .endm #else # define TRACE_IRQS_OFF_DEBUG TRACE_IRQS_OFF # define TRACE_IRQS_ON_DEBUG TRACE_IRQS_ON # define TRACE_IRQS_IRETQ_DEBUG TRACE_IRQS_IRETQ #endif /* * 64-bit SYSCALL instruction entry. Up to 6 arguments in registers. * * This is the only entry point used for 64-bit system calls. The * hardware interface is reasonably well designed and the register to * argument mapping Linux uses fits well with the registers that are * available when SYSCALL is used. * * SYSCALL instructions can be found inlined in libc implementations as * well as some other programs and libraries. There are also a handful * of SYSCALL instructions in the vDSO used, for example, as a * clock_gettimeofday fallback. * * 64-bit SYSCALL saves rip to rcx, clears rflags.RF, then saves rflags to r11, * then loads new ss, cs, and rip from previously programmed MSRs. * rflags gets masked by a value from another MSR (so CLD and CLAC * are not needed). SYSCALL does not save anything on the stack * and does not change rsp. * * Registers on entry: * rax system call number * rcx return address * r11 saved rflags (note: r11 is callee-clobbered register in C ABI) * rdi arg0 * rsi arg1 * rdx arg2 * r10 arg3 (needs to be moved to rcx to conform to C ABI) * r8 arg4 * r9 arg5 * (note: r12-r15, rbp, rbx are callee-preserved in C ABI) * * Only called from user space. * * When user can change pt_regs->foo always force IRET. That is because * it deals with uncanonical addresses better. SYSRET has trouble * with them due to bugs in both AMD and Intel CPUs. */ ENTRY(entry_SYSCALL_64) /* * Interrupts are off on entry. * We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON, * it is too small to ever cause noticeable irq latency. */ SWAPGS_UNSAFE_STACK SWITCH_KERNEL_CR3_NO_STACK /* * A hypervisor implementation might want to use a label * after the swapgs, so that it can do the swapgs * for the guest and jump here on syscall. */ GLOBAL(entry_SYSCALL_64_after_swapgs) movq %rsp, PER_CPU_VAR(rsp_scratch) movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp TRACE_IRQS_OFF /* Construct struct pt_regs on stack */ pushq $__USER_DS /* pt_regs->ss */ pushq PER_CPU_VAR(rsp_scratch) /* pt_regs->sp */ pushq %r11 /* pt_regs->flags */ pushq $__USER_CS /* pt_regs->cs */ pushq %rcx /* pt_regs->ip */ pushq %rax /* pt_regs->orig_ax */ pushq %rdi /* pt_regs->di */ pushq %rsi /* pt_regs->si */ pushq %rdx /* pt_regs->dx */ pushq %rcx /* pt_regs->cx */ pushq $-ENOSYS /* pt_regs->ax */ pushq %r8 /* pt_regs->r8 */ pushq %r9 /* pt_regs->r9 */ pushq %r10 /* pt_regs->r10 */ /* * Clear extra registers that a speculation attack might * otherwise want to exploit. Interleave XOR with PUSH * for better uop scheduling: */ xorq %r10, %r10 /* nospec r10 */ pushq %r11 /* pt_regs->r11 */ xorq %r11, %r11 /* nospec r11 */ pushq %rbx /* pt_regs->rbx */ xorl %ebx, %ebx /* nospec rbx */ pushq %rbp /* pt_regs->rbp */ xorl %ebp, %ebp /* nospec rbp */ pushq %r12 /* pt_regs->r12 */ xorq %r12, %r12 /* nospec r12 */ pushq %r13 /* pt_regs->r13 */ xorq %r13, %r13 /* nospec r13 */ pushq %r14 /* pt_regs->r14 */ xorq %r14, %r14 /* nospec r14 */ pushq %r15 /* pt_regs->r15 */ xorq %r15, %r15 /* nospec r15 */ /* IRQs are off. */ movq %rsp, %rdi call do_syscall_64 /* returns with IRQs disabled */ RESTORE_EXTRA_REGS TRACE_IRQS_IRETQ /* we're about to change IF */ /* * Try to use SYSRET instead of IRET if we're returning to * a completely clean 64-bit userspace context. */ movq RCX(%rsp), %rcx movq RIP(%rsp), %r11 cmpq %rcx, %r11 /* RCX == RIP */ jne opportunistic_sysret_failed /* * On Intel CPUs, SYSRET with non-canonical RCX/RIP will #GP * in kernel space. This essentially lets the user take over * the kernel, since userspace controls RSP. * * If width of "canonical tail" ever becomes variable, this will need * to be updated to remain correct on both old and new CPUs. */ .ifne __VIRTUAL_MASK_SHIFT - 47 .error "virtual address width changed -- SYSRET checks need update" .endif /* Change top 16 bits to be the sign-extension of 47th bit */ shl $(64 - (__VIRTUAL_MASK_SHIFT+1)), %rcx sar $(64 - (__VIRTUAL_MASK_SHIFT+1)), %rcx /* If this changed %rcx, it was not canonical */ cmpq %rcx, %r11 jne opportunistic_sysret_failed cmpq $__USER_CS, CS(%rsp) /* CS must match SYSRET */ jne opportunistic_sysret_failed movq R11(%rsp), %r11 cmpq %r11, EFLAGS(%rsp) /* R11 == RFLAGS */ jne opportunistic_sysret_failed /* * SYSCALL clears RF when it saves RFLAGS in R11 and SYSRET cannot * restore RF properly. If the slowpath sets it for whatever reason, we * need to restore it correctly. * * SYSRET can restore TF, but unlike IRET, restoring TF results in a * trap from userspace immediately after SYSRET. This would cause an * infinite loop whenever #DB happens with register state that satisfies * the opportunistic SYSRET conditions. For example, single-stepping * this user code: * * movq $stuck_here, %rcx * pushfq * popq %r11 * stuck_here: * * would never get past 'stuck_here'. */ testq $(X86_EFLAGS_RF|X86_EFLAGS_TF), %r11 jnz opportunistic_sysret_failed /* nothing to check for RSP */ cmpq $__USER_DS, SS(%rsp) /* SS must match SYSRET */ jne opportunistic_sysret_failed /* * We win! This label is here just for ease of understanding * perf profiles. Nothing jumps here. */ syscall_return_via_sysret: /* rcx and r11 are already restored (see code above) */ RESTORE_C_REGS_EXCEPT_RCX_R11 /* * This opens a window where we have a user CR3, but are * running in the kernel. This makes using the CS * register useless for telling whether or not we need to * switch CR3 in NMIs. Normal interrupts are OK because * they are off here. */ SWITCH_USER_CR3 movq RSP(%rsp), %rsp USERGS_SYSRET64 opportunistic_sysret_failed: /* * This opens a window where we have a user CR3, but are * running in the kernel. This makes using the CS * register useless for telling whether or not we need to * switch CR3 in NMIs. Normal interrupts are OK because * they are off here. */ SWITCH_USER_CR3 SWAPGS jmp restore_c_regs_and_iret END(entry_SYSCALL_64) /* * %rdi: prev task * %rsi: next task */ ENTRY(__switch_to_asm) /* * Save callee-saved registers * This must match the order in inactive_task_frame */ pushq %rbp pushq %rbx pushq %r12 pushq %r13 pushq %r14 pushq %r15 pushfq /* switch stack */ movq %rsp, TASK_threadsp(%rdi) movq TASK_threadsp(%rsi), %rsp #ifdef CONFIG_CC_STACKPROTECTOR movq TASK_stack_canary(%rsi), %rbx movq %rbx, PER_CPU_VAR(irq_stack_union)+stack_canary_offset #endif #ifdef CONFIG_RETPOLINE /* * When switching from a shallower to a deeper call stack * the RSB may either underflow or use entries populated * with userspace addresses. On CPUs where those concerns * exist, overwrite the RSB with entries which capture * speculative execution to prevent attack. */ FILL_RETURN_BUFFER %r12, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_CTXSW #endif /* restore callee-saved registers */ popfq popq %r15 popq %r14 popq %r13 popq %r12 popq %rbx popq %rbp jmp __switch_to END(__switch_to_asm) /* * A newly forked process directly context switches into this address. * * rax: prev task we switched from * rbx: kernel thread func (NULL for user thread) * r12: kernel thread arg */ ENTRY(ret_from_fork) movq %rax, %rdi call schedule_tail /* rdi: 'prev' task parameter */ testq %rbx, %rbx /* from kernel_thread? */ jnz 1f /* kernel threads are uncommon */ 2: movq %rsp, %rdi call syscall_return_slowpath /* returns with IRQs disabled */ TRACE_IRQS_ON /* user mode is traced as IRQS on */ SWITCH_USER_CR3 SWAPGS jmp restore_regs_and_iret 1: /* kernel thread */ movq %r12, %rdi CALL_NOSPEC %rbx /* * A kernel thread is allowed to return here after successfully * calling do_execve(). Exit to userspace to complete the execve() * syscall. */ movq $0, RAX(%rsp) jmp 2b END(ret_from_fork) /* * Build the entry stubs with some assembler magic. * We pack 1 stub into every 8-byte block. */ .align 8 ENTRY(irq_entries_start) vector=FIRST_EXTERNAL_VECTOR .rept (FIRST_SYSTEM_VECTOR - FIRST_EXTERNAL_VECTOR) pushq $(~vector+0x80) /* Note: always in signed byte range */ vector=vector+1 jmp common_interrupt .align 8 .endr END(irq_entries_start) /* * Interrupt entry/exit. * * Interrupt entry points save only callee clobbered registers in fast path. * * Entry runs with interrupts off. */ /* 0(%rsp): ~(interrupt number) */ .macro interrupt func cld ALLOC_PT_GPREGS_ON_STACK SAVE_C_REGS SAVE_EXTRA_REGS testb $3, CS(%rsp) jz 1f /* * IRQ from user mode. Switch to kernel gsbase and inform context * tracking that we're in kernel mode. */ SWAPGS FENCE_SWAPGS_USER_ENTRY SWITCH_KERNEL_CR3 /* * We need to tell lockdep that IRQs are off. We can't do this until * we fix gsbase, and we should do it before enter_from_user_mode * (which can take locks). Since TRACE_IRQS_OFF idempotent, * the simplest way to handle it is to just call it twice if * we enter from user mode. There's no reason to optimize this since * TRACE_IRQS_OFF is a no-op if lockdep is off. */ TRACE_IRQS_OFF CALL_enter_from_user_mode jmp 2f 1: FENCE_SWAPGS_KERNEL_ENTRY 2: /* * Save previous stack pointer, optionally switch to interrupt stack. * irq_count is used to check if a CPU is already on an interrupt stack * or not. While this is essentially redundant with preempt_count it is * a little cheaper to use a separate counter in the PDA (short of * moving irq_enter into assembly, which would be too much work) */ movq %rsp, %rdi incl PER_CPU_VAR(irq_count) cmovzq PER_CPU_VAR(irq_stack_ptr), %rsp pushq %rdi /* We entered an interrupt context - irqs are off: */ TRACE_IRQS_OFF call \func /* rdi points to pt_regs */ .endm /* * The interrupt stubs push (~vector+0x80) onto the stack and * then jump to common_interrupt. */ .p2align CONFIG_X86_L1_CACHE_SHIFT common_interrupt: ASM_CLAC addq $-0x80, (%rsp) /* Adjust vector to [-256, -1] range */ interrupt do_IRQ /* 0(%rsp): old RSP */ ret_from_intr: DISABLE_INTERRUPTS(CLBR_NONE) TRACE_IRQS_OFF decl PER_CPU_VAR(irq_count) /* Restore saved previous stack */ popq %rsp testb $3, CS(%rsp) jz retint_kernel /* Interrupt came from user space */ GLOBAL(retint_user) mov %rsp,%rdi call prepare_exit_to_usermode TRACE_IRQS_IRETQ SWITCH_USER_CR3 SWAPGS jmp restore_regs_and_iret /* Returning to kernel space */ retint_kernel: #ifdef CONFIG_PREEMPT /* Interrupts are off */ /* Check if we need preemption */ btl $9, EFLAGS(%rsp) /* were interrupts off? */ jnc 1f 0: cmpl $0, PER_CPU_VAR(__preempt_count) jnz 1f call preempt_schedule_irq jmp 0b 1: #endif /* * The iretq could re-enable interrupts: */ TRACE_IRQS_IRETQ /* * At this label, code paths which return to kernel and to user, * which come from interrupts/exception and from syscalls, merge. */ GLOBAL(restore_regs_and_iret) RESTORE_EXTRA_REGS restore_c_regs_and_iret: RESTORE_C_REGS REMOVE_PT_GPREGS_FROM_STACK 8 INTERRUPT_RETURN ENTRY(native_iret) /* * Are we returning to a stack segment from the LDT? Note: in * 64-bit mode SS:RSP on the exception stack is always valid. */ #ifdef CONFIG_X86_ESPFIX64 testb $4, (SS-RIP)(%rsp) jnz native_irq_return_ldt #endif .global native_irq_return_iret native_irq_return_iret: /* * This may fault. Non-paranoid faults on return to userspace are * handled by fixup_bad_iret. These include #SS, #GP, and #NP. * Double-faults due to espfix64 are handled in do_double_fault. * Other faults here are fatal. */ iretq #ifdef CONFIG_X86_ESPFIX64 native_irq_return_ldt: /* * We are running with user GSBASE. All GPRs contain their user * values. We have a percpu ESPFIX stack that is eight slots * long (see ESPFIX_STACK_SIZE). espfix_waddr points to the bottom * of the ESPFIX stack. * * We clobber RAX and RDI in this code. We stash RDI on the * normal stack and RAX on the ESPFIX stack. * * The ESPFIX stack layout we set up looks like this: * * --- top of ESPFIX stack --- * SS * RSP * RFLAGS * CS * RIP <-- RSP points here when we're done * RAX <-- espfix_waddr points here * --- bottom of ESPFIX stack --- */ pushq %rdi /* Stash user RDI */ SWAPGS SWITCH_KERNEL_CR3 movq PER_CPU_VAR(espfix_waddr), %rdi movq %rax, (0*8)(%rdi) /* user RAX */ movq (1*8)(%rsp), %rax /* user RIP */ movq %rax, (1*8)(%rdi) movq (2*8)(%rsp), %rax /* user CS */ movq %rax, (2*8)(%rdi) movq (3*8)(%rsp), %rax /* user RFLAGS */ movq %rax, (3*8)(%rdi) movq (5*8)(%rsp), %rax /* user SS */ movq %rax, (5*8)(%rdi) movq (4*8)(%rsp), %rax /* user RSP */ movq %rax, (4*8)(%rdi) /* Now RAX == RSP. */ andl $0xffff0000, %eax /* RAX = (RSP & 0xffff0000) */ popq %rdi /* Restore user RDI */ /* * espfix_stack[31:16] == 0. The page tables are set up such that * (espfix_stack | (X & 0xffff0000)) points to a read-only alias of * espfix_waddr for any X. That is, there are 65536 RO aliases of * the same page. Set up RSP so that RSP[31:16] contains the * respective 16 bits of the /userspace/ RSP and RSP nonetheless * still points to an RO alias of the ESPFIX stack. */ orq PER_CPU_VAR(espfix_stack), %rax SWITCH_USER_CR3 SWAPGS movq %rax, %rsp /* * At this point, we cannot write to the stack any more, but we can * still read. */ popq %rax /* Restore user RAX */ /* * RSP now points to an ordinary IRET frame, except that the page * is read-only and RSP[31:16] are preloaded with the userspace * values. We can now IRET back to userspace. */ jmp native_irq_return_iret #endif END(common_interrupt) /* * APIC interrupts. */ .macro apicinterrupt3 num sym do_sym ENTRY(\sym) ASM_CLAC pushq $~(\num) .Lcommon_\sym: interrupt \do_sym jmp ret_from_intr END(\sym) .endm #ifdef CONFIG_TRACING #define trace(sym) trace_##sym #define smp_trace(sym) smp_trace_##sym .macro trace_apicinterrupt num sym apicinterrupt3 \num trace(\sym) smp_trace(\sym) .endm #else .macro trace_apicinterrupt num sym do_sym .endm #endif /* Make sure APIC interrupt handlers end up in the irqentry section: */ #define PUSH_SECTION_IRQENTRY .pushsection .irqentry.text, "ax" #define POP_SECTION_IRQENTRY .popsection .macro apicinterrupt num sym do_sym PUSH_SECTION_IRQENTRY apicinterrupt3 \num \sym \do_sym trace_apicinterrupt \num \sym POP_SECTION_IRQENTRY .endm #ifdef CONFIG_SMP apicinterrupt3 IRQ_MOVE_CLEANUP_VECTOR irq_move_cleanup_interrupt smp_irq_move_cleanup_interrupt apicinterrupt3 REBOOT_VECTOR reboot_interrupt smp_reboot_interrupt #endif #ifdef CONFIG_X86_UV apicinterrupt3 UV_BAU_MESSAGE uv_bau_message_intr1 uv_bau_message_interrupt #endif apicinterrupt LOCAL_TIMER_VECTOR apic_timer_interrupt smp_apic_timer_interrupt apicinterrupt X86_PLATFORM_IPI_VECTOR x86_platform_ipi smp_x86_platform_ipi #ifdef CONFIG_HAVE_KVM apicinterrupt3 POSTED_INTR_VECTOR kvm_posted_intr_ipi smp_kvm_posted_intr_ipi apicinterrupt3 POSTED_INTR_WAKEUP_VECTOR kvm_posted_intr_wakeup_ipi smp_kvm_posted_intr_wakeup_ipi #endif #ifdef CONFIG_X86_MCE_THRESHOLD apicinterrupt THRESHOLD_APIC_VECTOR threshold_interrupt smp_threshold_interrupt #endif #ifdef CONFIG_X86_MCE_AMD apicinterrupt DEFERRED_ERROR_VECTOR deferred_error_interrupt smp_deferred_error_interrupt #endif #ifdef CONFIG_X86_THERMAL_VECTOR apicinterrupt THERMAL_APIC_VECTOR thermal_interrupt smp_thermal_interrupt #endif #ifdef CONFIG_SMP apicinterrupt CALL_FUNCTION_SINGLE_VECTOR call_function_single_interrupt smp_call_function_single_interrupt apicinterrupt CALL_FUNCTION_VECTOR call_function_interrupt smp_call_function_interrupt apicinterrupt RESCHEDULE_VECTOR reschedule_interrupt smp_reschedule_interrupt #endif apicinterrupt ERROR_APIC_VECTOR error_interrupt smp_error_interrupt apicinterrupt SPURIOUS_APIC_VECTOR spurious_interrupt smp_spurious_interrupt #ifdef CONFIG_IRQ_WORK apicinterrupt IRQ_WORK_VECTOR irq_work_interrupt smp_irq_work_interrupt #endif /* * Exception entry points. */ #define CPU_TSS_IST(x) PER_CPU_VAR(cpu_tss) + (TSS_ist + ((x) - 1) * 8) .macro idtentry sym do_sym has_error_code:req paranoid=0 shift_ist=-1 ENTRY(\sym) /* Sanity check */ .if \shift_ist != -1 && \paranoid == 0 .error "using shift_ist requires paranoid=1" .endif ASM_CLAC PARAVIRT_ADJUST_EXCEPTION_FRAME .ifeq \has_error_code pushq $-1 /* ORIG_RAX: no syscall to restart */ .endif ALLOC_PT_GPREGS_ON_STACK .if \paranoid .if \paranoid == 1 testb $3, CS(%rsp) /* If coming from userspace, switch stacks */ jnz 1f .endif call paranoid_entry .else call error_entry .endif /* returned flag: ebx=0: need swapgs on exit, ebx=1: don't need it */ .if \paranoid .if \shift_ist != -1 TRACE_IRQS_OFF_DEBUG /* reload IDT in case of recursion */ .else TRACE_IRQS_OFF .endif .endif movq %rsp, %rdi /* pt_regs pointer */ .if \has_error_code movq ORIG_RAX(%rsp), %rsi /* get error code */ movq $-1, ORIG_RAX(%rsp) /* no syscall to restart */ .else xorl %esi, %esi /* no error code */ .endif .if \shift_ist != -1 subq $EXCEPTION_STKSZ, CPU_TSS_IST(\shift_ist) .endif call \do_sym .if \shift_ist != -1 addq $EXCEPTION_STKSZ, CPU_TSS_IST(\shift_ist) .endif /* these procedures expect "no swapgs" flag in ebx */ .if \paranoid jmp paranoid_exit .else jmp error_exit .endif .if \paranoid == 1 /* * Paranoid entry from userspace. Switch stacks and treat it * as a normal entry. This means that paranoid handlers * run in real process context if user_mode(regs). */ 1: call error_entry movq %rsp, %rdi /* pt_regs pointer */ call sync_regs movq %rax, %rsp /* switch stack */ movq %rsp, %rdi /* pt_regs pointer */ .if \has_error_code movq ORIG_RAX(%rsp), %rsi /* get error code */ movq $-1, ORIG_RAX(%rsp) /* no syscall to restart */ .else xorl %esi, %esi /* no error code */ .endif call \do_sym jmp error_exit .endif END(\sym) .endm #ifdef CONFIG_TRACING .macro trace_idtentry sym do_sym has_error_code:req idtentry trace(\sym) trace(\do_sym) has_error_code=\has_error_code idtentry \sym \do_sym has_error_code=\has_error_code .endm #else .macro trace_idtentry sym do_sym has_error_code:req idtentry \sym \do_sym has_error_code=\has_error_code .endm #endif idtentry divide_error do_divide_error has_error_code=0 idtentry overflow do_overflow has_error_code=0 idtentry bounds do_bounds has_error_code=0 idtentry invalid_op do_invalid_op has_error_code=0 idtentry device_not_available do_device_not_available has_error_code=0 idtentry double_fault do_double_fault has_error_code=1 paranoid=2 idtentry coprocessor_segment_overrun do_coprocessor_segment_overrun has_error_code=0 idtentry invalid_TSS do_invalid_TSS has_error_code=1 idtentry segment_not_present do_segment_not_present has_error_code=1 idtentry spurious_interrupt_bug do_spurious_interrupt_bug has_error_code=0 idtentry coprocessor_error do_coprocessor_error has_error_code=0 idtentry alignment_check do_alignment_check has_error_code=1 idtentry simd_coprocessor_error do_simd_coprocessor_error has_error_code=0 /* * Reload gs selector with exception handling * edi: new selector */ ENTRY(native_load_gs_index) pushfq DISABLE_INTERRUPTS(CLBR_ANY & ~CLBR_RDI) SWAPGS .Lgs_change: movl %edi, %gs 2: ALTERNATIVE "", "mfence", X86_BUG_SWAPGS_FENCE SWAPGS popfq ret END(native_load_gs_index) EXPORT_SYMBOL(native_load_gs_index) _ASM_EXTABLE(.Lgs_change, bad_gs) .section .fixup, "ax" /* running with kernelgs */ bad_gs: SWAPGS /* switch back to user gs */ .macro ZAP_GS /* This can't be a string because the preprocessor needs to see it. */ movl $__USER_DS, %eax movl %eax, %gs .endm ALTERNATIVE "", "ZAP_GS", X86_BUG_NULL_SEG xorl %eax, %eax movl %eax, %gs jmp 2b .previous /* Call softirq on interrupt stack. Interrupts are off. */ ENTRY(do_softirq_own_stack) pushq %rbp mov %rsp, %rbp incl PER_CPU_VAR(irq_count) cmove PER_CPU_VAR(irq_stack_ptr), %rsp push %rbp /* frame pointer backlink */ call __do_softirq leaveq decl PER_CPU_VAR(irq_count) ret END(do_softirq_own_stack) #ifdef CONFIG_XEN idtentry xen_hypervisor_callback xen_do_hypervisor_callback has_error_code=0 /* * A note on the "critical region" in our callback handler. * We want to avoid stacking callback handlers due to events occurring * during handling of the last event. To do this, we keep events disabled * until we've done all processing. HOWEVER, we must enable events before * popping the stack frame (can't be done atomically) and so it would still * be possible to get enough handler activations to overflow the stack. * Although unlikely, bugs of that kind are hard to track down, so we'd * like to avoid the possibility. * So, on entry to the handler we detect whether we interrupted an * existing activation in its critical region -- if so, we pop the current * activation and restart the handler using the previous one. */ ENTRY(xen_do_hypervisor_callback) /* do_hypervisor_callback(struct *pt_regs) */ /* * Since we don't modify %rdi, evtchn_do_upall(struct *pt_regs) will * see the correct pointer to the pt_regs */ movq %rdi, %rsp /* we don't return, adjust the stack frame */ 11: incl PER_CPU_VAR(irq_count) movq %rsp, %rbp cmovzq PER_CPU_VAR(irq_stack_ptr), %rsp pushq %rbp /* frame pointer backlink */ call xen_evtchn_do_upcall popq %rsp decl PER_CPU_VAR(irq_count) #ifndef CONFIG_PREEMPT call xen_maybe_preempt_hcall #endif jmp error_exit END(xen_do_hypervisor_callback) /* * Hypervisor uses this for application faults while it executes. * We get here for two reasons: * 1. Fault while reloading DS, ES, FS or GS * 2. Fault while executing IRET * Category 1 we do not need to fix up as Xen has already reloaded all segment * registers that could be reloaded and zeroed the others. * Category 2 we fix up by killing the current process. We cannot use the * normal Linux return path in this case because if we use the IRET hypercall * to pop the stack frame we end up in an infinite loop of failsafe callbacks. * We distinguish between categories by comparing each saved segment register * with its current contents: any discrepancy means we in category 1. */ ENTRY(xen_failsafe_callback) movl %ds, %ecx cmpw %cx, 0x10(%rsp) jne 1f movl %es, %ecx cmpw %cx, 0x18(%rsp) jne 1f movl %fs, %ecx cmpw %cx, 0x20(%rsp) jne 1f movl %gs, %ecx cmpw %cx, 0x28(%rsp) jne 1f /* All segments match their saved values => Category 2 (Bad IRET). */ movq (%rsp), %rcx movq 8(%rsp), %r11 addq $0x30, %rsp pushq $0 /* RIP */ pushq %r11 pushq %rcx jmp general_protection 1: /* Segment mismatch => Category 1 (Bad segment). Retry the IRET. */ movq (%rsp), %rcx movq 8(%rsp), %r11 addq $0x30, %rsp pushq $-1 /* orig_ax = -1 => not a system call */ ALLOC_PT_GPREGS_ON_STACK SAVE_C_REGS SAVE_EXTRA_REGS jmp error_exit END(xen_failsafe_callback) apicinterrupt3 HYPERVISOR_CALLBACK_VECTOR \ xen_hvm_callback_vector xen_evtchn_do_upcall #endif /* CONFIG_XEN */ #if IS_ENABLED(CONFIG_HYPERV) apicinterrupt3 HYPERVISOR_CALLBACK_VECTOR \ hyperv_callback_vector hyperv_vector_handler #endif /* CONFIG_HYPERV */ idtentry debug do_debug has_error_code=0 paranoid=1 shift_ist=DEBUG_STACK idtentry int3 do_int3 has_error_code=0 idtentry stack_segment do_stack_segment has_error_code=1 #ifdef CONFIG_XEN idtentry xen_debug do_debug has_error_code=0 idtentry xen_int3 do_int3 has_error_code=0 idtentry xen_stack_segment do_stack_segment has_error_code=1 #endif idtentry general_protection do_general_protection has_error_code=1 trace_idtentry page_fault do_page_fault has_error_code=1 #ifdef CONFIG_KVM_GUEST idtentry async_page_fault do_async_page_fault has_error_code=1 #endif #ifdef CONFIG_X86_MCE idtentry machine_check do_mce has_error_code=0 paranoid=1 #endif /* * Save all registers in pt_regs, and switch gs if needed. * Use slow, but surefire "are we in kernel?" check. * * Return: ebx=0: needs swapgs but not SWITCH_USER_CR3 in paranoid_exit * ebx=1: needs neither swapgs nor SWITCH_USER_CR3 in paranoid_exit * ebx=2: needs both swapgs and SWITCH_USER_CR3 in paranoid_exit * ebx=3: needs SWITCH_USER_CR3 but not swapgs in paranoid_exit */ ENTRY(paranoid_entry) cld SAVE_C_REGS 8 SAVE_EXTRA_REGS 8 movl $1, %ebx movl $MSR_GS_BASE, %ecx rdmsr testl %edx, %edx js 1f /* negative -> in kernel */ SWAPGS xorl %ebx, %ebx 1: #ifdef CONFIG_PAGE_TABLE_ISOLATION /* * We might have come in between a swapgs and a SWITCH_KERNEL_CR3 * on entry, or between a SWITCH_USER_CR3 and a swapgs on exit. * Do a conditional SWITCH_KERNEL_CR3: this could safely be done * unconditionally, but we need to find out whether the reverse * should be done on return (conveyed to paranoid_exit in %ebx). */ ALTERNATIVE "jmp 2f", "movq %cr3, %rax", X86_FEATURE_KAISER testl $KAISER_SHADOW_PGD_OFFSET, %eax jz 2f orl $2, %ebx andq $(~(X86_CR3_PCID_ASID_MASK | KAISER_SHADOW_PGD_OFFSET)), %rax /* If PCID enabled, set X86_CR3_PCID_NOFLUSH_BIT */ ALTERNATIVE "", "bts $63, %rax", X86_FEATURE_PCID movq %rax, %cr3 2: #endif /* * The above doesn't do an unconditional CR3 write, even in the PTI * case. So do an lfence to prevent GS speculation, regardless of * whether PTI is enabled. */ FENCE_SWAPGS_KERNEL_ENTRY ret END(paranoid_entry) /* * "Paranoid" exit path from exception stack. This is invoked * only on return from non-NMI IST interrupts that came * from kernel space. * * We may be returning to very strange contexts (e.g. very early * in syscall entry), so checking for preemption here would * be complicated. Fortunately, we there's no good reason * to try to handle preemption here. * * On entry: ebx=0: needs swapgs but not SWITCH_USER_CR3 * ebx=1: needs neither swapgs nor SWITCH_USER_CR3 * ebx=2: needs both swapgs and SWITCH_USER_CR3 * ebx=3: needs SWITCH_USER_CR3 but not swapgs */ ENTRY(paranoid_exit) DISABLE_INTERRUPTS(CLBR_NONE) TRACE_IRQS_OFF_DEBUG TRACE_IRQS_IRETQ_DEBUG #ifdef CONFIG_PAGE_TABLE_ISOLATION /* No ALTERNATIVE for X86_FEATURE_KAISER: paranoid_entry sets %ebx */ testl $2, %ebx /* SWITCH_USER_CR3 needed? */ jz paranoid_exit_no_switch SWITCH_USER_CR3 paranoid_exit_no_switch: #endif testl $1, %ebx /* swapgs needed? */ jnz paranoid_exit_no_swapgs SWAPGS_UNSAFE_STACK paranoid_exit_no_swapgs: RESTORE_EXTRA_REGS RESTORE_C_REGS REMOVE_PT_GPREGS_FROM_STACK 8 INTERRUPT_RETURN END(paranoid_exit) /* * Save all registers in pt_regs, and switch gs if needed. */ ENTRY(error_entry) cld SAVE_C_REGS 8 SAVE_EXTRA_REGS 8 /* * error_entry() always returns with a kernel gsbase and * CR3. We must also have a kernel CR3/gsbase before * calling TRACE_IRQS_*. Just unconditionally switch to * the kernel CR3 here. */ SWITCH_KERNEL_CR3 testb $3, CS+8(%rsp) jz .Lerror_kernelspace /* * We entered from user mode or we're pretending to have entered * from user mode due to an IRET fault. */ SWAPGS FENCE_SWAPGS_USER_ENTRY .Lerror_entry_from_usermode_after_swapgs: /* * We need to tell lockdep that IRQs are off. We can't do this until * we fix gsbase, and we should do it before enter_from_user_mode * (which can take locks). */ TRACE_IRQS_OFF CALL_enter_from_user_mode ret .Lerror_entry_done_lfence: FENCE_SWAPGS_KERNEL_ENTRY .Lerror_entry_done: TRACE_IRQS_OFF ret /* * There are two places in the kernel that can potentially fault with * usergs. Handle them here. B stepping K8s sometimes report a * truncated RIP for IRET exceptions returning to compat mode. Check * for these here too. */ .Lerror_kernelspace: leaq native_irq_return_iret(%rip), %rcx cmpq %rcx, RIP+8(%rsp) je .Lerror_bad_iret movl %ecx, %eax /* zero extend */ cmpq %rax, RIP+8(%rsp) je .Lbstep_iret cmpq $.Lgs_change, RIP+8(%rsp) jne .Lerror_entry_done_lfence /* * hack: .Lgs_change can fail with user gsbase. If this happens, fix up * gsbase and proceed. We'll fix up the exception and land in * .Lgs_change's error handler with kernel gsbase. */ SWAPGS FENCE_SWAPGS_USER_ENTRY jmp .Lerror_entry_done .Lbstep_iret: /* Fix truncated RIP */ movq %rcx, RIP+8(%rsp) /* fall through */ .Lerror_bad_iret: /* * We came from an IRET to user mode, so we have user gsbase. * Switch to kernel gsbase: */ SWAPGS FENCE_SWAPGS_USER_ENTRY /* * Pretend that the exception came from user mode: set up pt_regs * as if we faulted immediately after IRET. */ mov %rsp, %rdi call fixup_bad_iret mov %rax, %rsp jmp .Lerror_entry_from_usermode_after_swapgs END(error_entry) ENTRY(error_exit) DISABLE_INTERRUPTS(CLBR_NONE) TRACE_IRQS_OFF testb $3, CS(%rsp) jz retint_kernel jmp retint_user END(error_exit) /* Runs on exception stack */ ENTRY(nmi) /* * Fix up the exception frame if we're on Xen. * PARAVIRT_ADJUST_EXCEPTION_FRAME is guaranteed to push at most * one value to the stack on native, so it may clobber the rdx * scratch slot, but it won't clobber any of the important * slots past it. * * Xen is a different story, because the Xen frame itself overlaps * the "NMI executing" variable. */ PARAVIRT_ADJUST_EXCEPTION_FRAME /* * We allow breakpoints in NMIs. If a breakpoint occurs, then * the iretq it performs will take us out of NMI context. * This means that we can have nested NMIs where the next * NMI is using the top of the stack of the previous NMI. We * can't let it execute because the nested NMI will corrupt the * stack of the previous NMI. NMI handlers are not re-entrant * anyway. * * To handle this case we do the following: * Check the a special location on the stack that contains * a variable that is set when NMIs are executing. * The interrupted task's stack is also checked to see if it * is an NMI stack. * If the variable is not set and the stack is not the NMI * stack then: * o Set the special variable on the stack * o Copy the interrupt frame into an "outermost" location on the * stack * o Copy the interrupt frame into an "iret" location on the stack * o Continue processing the NMI * If the variable is set or the previous stack is the NMI stack: * o Modify the "iret" location to jump to the repeat_nmi * o return back to the first NMI * * Now on exit of the first NMI, we first clear the stack variable * The NMI stack will tell any nested NMIs at that point that it is * nested. Then we pop the stack normally with iret, and if there was * a nested NMI that updated the copy interrupt stack frame, a * jump will be made to the repeat_nmi code that will handle the second * NMI. * * However, espfix prevents us from directly returning to userspace * with a single IRET instruction. Similarly, IRET to user mode * can fault. We therefore handle NMIs from user space like * other IST entries. */ ASM_CLAC /* Use %rdx as our temp variable throughout */ pushq %rdx testb $3, CS-RIP+8(%rsp) jz .Lnmi_from_kernel /* * NMI from user mode. We need to run on the thread stack, but we * can't go through the normal entry paths: NMIs are masked, and * we don't want to enable interrupts, because then we'll end * up in an awkward situation in which IRQs are on but NMIs * are off. * * We also must not push anything to the stack before switching * stacks lest we corrupt the "NMI executing" variable. */ SWAPGS_UNSAFE_STACK /* * percpu variables are mapped with user CR3, so no need * to switch CR3 here. */ cld FENCE_SWAPGS_USER_ENTRY movq %rsp, %rdx movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp pushq 5*8(%rdx) /* pt_regs->ss */ pushq 4*8(%rdx) /* pt_regs->rsp */ pushq 3*8(%rdx) /* pt_regs->flags */ pushq 2*8(%rdx) /* pt_regs->cs */ pushq 1*8(%rdx) /* pt_regs->rip */ pushq $-1 /* pt_regs->orig_ax */ pushq %rdi /* pt_regs->di */ pushq %rsi /* pt_regs->si */ pushq (%rdx) /* pt_regs->dx */ pushq %rcx /* pt_regs->cx */ pushq %rax /* pt_regs->ax */ pushq %r8 /* pt_regs->r8 */ pushq %r9 /* pt_regs->r9 */ pushq %r10 /* pt_regs->r10 */ pushq %r11 /* pt_regs->r11 */ pushq %rbx /* pt_regs->rbx */ pushq %rbp /* pt_regs->rbp */ pushq %r12 /* pt_regs->r12 */ pushq %r13 /* pt_regs->r13 */ pushq %r14 /* pt_regs->r14 */ pushq %r15 /* pt_regs->r15 */ /* * At this point we no longer need to worry about stack damage * due to nesting -- we're on the normal thread stack and we're * done with the NMI stack. */ movq %rsp, %rdi movq $-1, %rsi #ifdef CONFIG_PAGE_TABLE_ISOLATION /* Unconditionally use kernel CR3 for do_nmi() */ /* %rax is saved above, so OK to clobber here */ ALTERNATIVE "jmp 2f", "movq %cr3, %rax", X86_FEATURE_KAISER /* If PCID enabled, NOFLUSH now and NOFLUSH on return */ ALTERNATIVE "", "bts $63, %rax", X86_FEATURE_PCID pushq %rax /* mask off "user" bit of pgd address and 12 PCID bits: */ andq $(~(X86_CR3_PCID_ASID_MASK | KAISER_SHADOW_PGD_OFFSET)), %rax movq %rax, %cr3 2: #endif call do_nmi #ifdef CONFIG_PAGE_TABLE_ISOLATION /* * Unconditionally restore CR3. I know we return to * kernel code that needs user CR3, but do we ever return * to "user mode" where we need the kernel CR3? */ ALTERNATIVE "", "popq %rax; movq %rax, %cr3", X86_FEATURE_KAISER #endif /* * Return back to user mode. We must *not* do the normal exit * work, because we don't want to enable interrupts. Do not * switch to user CR3: we might be going back to kernel code * that had a user CR3 set. */ SWAPGS jmp restore_c_regs_and_iret .Lnmi_from_kernel: /* * Here's what our stack frame will look like: * +---------------------------------------------------------+ * | original SS | * | original Return RSP | * | original RFLAGS | * | original CS | * | original RIP | * +---------------------------------------------------------+ * | temp storage for rdx | * +---------------------------------------------------------+ * | "NMI executing" variable | * +---------------------------------------------------------+ * | iret SS } Copied from "outermost" frame | * | iret Return RSP } on each loop iteration; overwritten | * | iret RFLAGS } by a nested NMI to force another | * | iret CS } iteration if needed. | * | iret RIP } | * +---------------------------------------------------------+ * | outermost SS } initialized in first_nmi; | * | outermost Return RSP } will not be changed before | * | outermost RFLAGS } NMI processing is done. | * | outermost CS } Copied to "iret" frame on each | * | outermost RIP } iteration. | * +---------------------------------------------------------+ * | pt_regs | * +---------------------------------------------------------+ * * The "original" frame is used by hardware. Before re-enabling * NMIs, we need to be done with it, and we need to leave enough * space for the asm code here. * * We return by executing IRET while RSP points to the "iret" frame. * That will either return for real or it will loop back into NMI * processing. * * The "outermost" frame is copied to the "iret" frame on each * iteration of the loop, so each iteration starts with the "iret" * frame pointing to the final return target. */ /* * Determine whether we're a nested NMI. * * If we interrupted kernel code between repeat_nmi and * end_repeat_nmi, then we are a nested NMI. We must not * modify the "iret" frame because it's being written by * the outer NMI. That's okay; the outer NMI handler is * about to about to call do_nmi anyway, so we can just * resume the outer NMI. */ movq $repeat_nmi, %rdx cmpq 8(%rsp), %rdx ja 1f movq $end_repeat_nmi, %rdx cmpq 8(%rsp), %rdx ja nested_nmi_out 1: /* * Now check "NMI executing". If it's set, then we're nested. * This will not detect if we interrupted an outer NMI just * before IRET. */ cmpl $1, -8(%rsp) je nested_nmi /* * Now test if the previous stack was an NMI stack. This covers * the case where we interrupt an outer NMI after it clears * "NMI executing" but before IRET. We need to be careful, though: * there is one case in which RSP could point to the NMI stack * despite there being no NMI active: naughty userspace controls * RSP at the very beginning of the SYSCALL targets. We can * pull a fast one on naughty userspace, though: we program * SYSCALL to mask DF, so userspace cannot cause DF to be set * if it controls the kernel's RSP. We set DF before we clear * "NMI executing". */ lea 6*8(%rsp), %rdx /* Compare the NMI stack (rdx) with the stack we came from (4*8(%rsp)) */ cmpq %rdx, 4*8(%rsp) /* If the stack pointer is above the NMI stack, this is a normal NMI */ ja first_nmi subq $EXCEPTION_STKSZ, %rdx cmpq %rdx, 4*8(%rsp) /* If it is below the NMI stack, it is a normal NMI */ jb first_nmi /* Ah, it is within the NMI stack. */ testb $(X86_EFLAGS_DF >> 8), (3*8 + 1)(%rsp) jz first_nmi /* RSP was user controlled. */ /* This is a nested NMI. */ nested_nmi: /* * Modify the "iret" frame to point to repeat_nmi, forcing another * iteration of NMI handling. */ subq $8, %rsp leaq -10*8(%rsp), %rdx pushq $__KERNEL_DS pushq %rdx pushfq pushq $__KERNEL_CS pushq $repeat_nmi /* Put stack back */ addq $(6*8), %rsp nested_nmi_out: popq %rdx /* We are returning to kernel mode, so this cannot result in a fault. */ INTERRUPT_RETURN first_nmi: /* Restore rdx. */ movq (%rsp), %rdx /* Make room for "NMI executing". */ pushq $0 /* Leave room for the "iret" frame */ subq $(5*8), %rsp /* Copy the "original" frame to the "outermost" frame */ .rept 5 pushq 11*8(%rsp) .endr /* Everything up to here is safe from nested NMIs */ #ifdef CONFIG_DEBUG_ENTRY /* * For ease of testing, unmask NMIs right away. Disabled by * default because IRET is very expensive. */ pushq $0 /* SS */ pushq %rsp /* RSP (minus 8 because of the previous push) */ addq $8, (%rsp) /* Fix up RSP */ pushfq /* RFLAGS */ pushq $__KERNEL_CS /* CS */ pushq $1f /* RIP */ INTERRUPT_RETURN /* continues at repeat_nmi below */ 1: #endif repeat_nmi: /* * If there was a nested NMI, the first NMI's iret will return * here. But NMIs are still enabled and we can take another * nested NMI. The nested NMI checks the interrupted RIP to see * if it is between repeat_nmi and end_repeat_nmi, and if so * it will just return, as we are about to repeat an NMI anyway. * This makes it safe to copy to the stack frame that a nested * NMI will update. * * RSP is pointing to "outermost RIP". gsbase is unknown, but, if * we're repeating an NMI, gsbase has the same value that it had on * the first iteration. paranoid_entry will load the kernel * gsbase if needed before we call do_nmi. "NMI executing" * is zero. */ movq $1, 10*8(%rsp) /* Set "NMI executing". */ /* * Copy the "outermost" frame to the "iret" frame. NMIs that nest * here must not modify the "iret" frame while we're writing to * it or it will end up containing garbage. */ addq $(10*8), %rsp .rept 5 pushq -6*8(%rsp) .endr subq $(5*8), %rsp end_repeat_nmi: /* * Everything below this point can be preempted by a nested NMI. * If this happens, then the inner NMI will change the "iret" * frame to point back to repeat_nmi. */ pushq $-1 /* ORIG_RAX: no syscall to restart */ ALLOC_PT_GPREGS_ON_STACK /* * Use the same approach as paranoid_entry to handle SWAPGS, but * without CR3 handling since we do that differently in NMIs. No * need to use paranoid_exit as we should not be calling schedule * in NMI context. Even with normal interrupts enabled. An NMI * should not be setting NEED_RESCHED or anything that normal * interrupts and exceptions might do. */ cld SAVE_C_REGS SAVE_EXTRA_REGS movl $1, %ebx movl $MSR_GS_BASE, %ecx rdmsr testl %edx, %edx js 1f /* negative -> in kernel */ SWAPGS xorl %ebx, %ebx 1: movq %rsp, %rdi movq $-1, %rsi #ifdef CONFIG_PAGE_TABLE_ISOLATION /* Unconditionally use kernel CR3 for do_nmi() */ /* %rax is saved above, so OK to clobber here */ ALTERNATIVE "jmp 2f", "movq %cr3, %rax", X86_FEATURE_KAISER /* If PCID enabled, NOFLUSH now and NOFLUSH on return */ ALTERNATIVE "", "bts $63, %rax", X86_FEATURE_PCID pushq %rax /* mask off "user" bit of pgd address and 12 PCID bits: */ andq $(~(X86_CR3_PCID_ASID_MASK | KAISER_SHADOW_PGD_OFFSET)), %rax movq %rax, %cr3 2: #endif FENCE_SWAPGS_KERNEL_ENTRY /* paranoidentry do_nmi, 0; without TRACE_IRQS_OFF */ call do_nmi #ifdef CONFIG_PAGE_TABLE_ISOLATION /* * Unconditionally restore CR3. We might be returning to * kernel code that needs user CR3, like just just before * a sysret. */ ALTERNATIVE "", "popq %rax; movq %rax, %cr3", X86_FEATURE_KAISER #endif testl %ebx, %ebx /* swapgs needed? */ jnz nmi_restore nmi_swapgs: /* We fixed up CR3 above, so no need to switch it here */ SWAPGS_UNSAFE_STACK nmi_restore: RESTORE_EXTRA_REGS RESTORE_C_REGS /* Point RSP at the "iret" frame. */ REMOVE_PT_GPREGS_FROM_STACK 6*8 /* * Clear "NMI executing". Set DF first so that we can easily * distinguish the remaining code between here and IRET from * the SYSCALL entry and exit paths. On a native kernel, we * could just inspect RIP, but, on paravirt kernels, * INTERRUPT_RETURN can translate into a jump into a * hypercall page. */ std movq $0, 5*8(%rsp) /* clear "NMI executing" */ /* * INTERRUPT_RETURN reads the "iret" frame and exits the NMI * stack in a single instruction. We are returning to kernel * mode, so this cannot result in a fault. */ INTERRUPT_RETURN END(nmi) ENTRY(ignore_sysret) mov $-ENOSYS, %eax sysret END(ignore_sysret) ENTRY(rewind_stack_do_exit) /* Prevent any naive code from trying to unwind to our caller. */ xorl %ebp, %ebp movq PER_CPU_VAR(cpu_current_top_of_stack), %rax leaq -TOP_OF_KERNEL_STACK_PADDING-PTREGS_SIZE(%rax), %rsp call do_exit 1: jmp 1b END(rewind_stack_do_exit)