/* * 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 /* 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 bt $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 bt $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 /* * 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 */ pushq %r11 /* pt_regs->r11 */ sub $(6*8), %rsp /* pt_regs->bp, bx, r12-15 not saved */ /* * If we need to do entry work or if we guess we'll need to do * exit work, go straight to the slow path. */ testl $_TIF_WORK_SYSCALL_ENTRY|_TIF_ALLWORK_MASK, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS) jnz entry_SYSCALL64_slow_path entry_SYSCALL_64_fastpath: /* * Easy case: enable interrupts and issue the syscall. If the syscall * needs pt_regs, we'll call a stub that disables interrupts again * and jumps to the slow path. */ TRACE_IRQS_ON ENABLE_INTERRUPTS(CLBR_NONE) #if __SYSCALL_MASK == ~0 cmpq $__NR_syscall_max, %rax #else andl $__SYSCALL_MASK, %eax cmpl $__NR_syscall_max, %eax #endif ja 1f /* return -ENOSYS (already in pt_regs->ax) */ movq %r10, %rcx /* * This call instruction is handled specially in stub_ptregs_64. * It might end up jumping to the slow path. If it jumps, RAX * and all argument registers are clobbered. */ call *sys_call_table(, %rax, 8) .Lentry_SYSCALL_64_after_fastpath_call: movq %rax, RAX(%rsp) 1: /* * If we get here, then we know that pt_regs is clean for SYSRET64. * If we see that no exit work is required (which we are required * to check with IRQs off), then we can go straight to SYSRET64. */ DISABLE_INTERRUPTS(CLBR_NONE) TRACE_IRQS_OFF testl $_TIF_ALLWORK_MASK, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS) jnz 1f LOCKDEP_SYS_EXIT TRACE_IRQS_ON /* user mode is traced as IRQs on */ movq RIP(%rsp), %rcx movq EFLAGS(%rsp), %r11 RESTORE_C_REGS_EXCEPT_RCX_R11 movq RSP(%rsp), %rsp USERGS_SYSRET64 1: /* * The fast path looked good when we started, but something changed * along the way and we need to switch to the slow path. Calling * raise(3) will trigger this, for example. IRQs are off. */ TRACE_IRQS_ON ENABLE_INTERRUPTS(CLBR_NONE) SAVE_EXTRA_REGS movq %rsp, %rdi call syscall_return_slowpath /* returns with IRQs disabled */ jmp return_from_SYSCALL_64 entry_SYSCALL64_slow_path: /* IRQs are off. */ SAVE_EXTRA_REGS movq %rsp, %rdi call do_syscall_64 /* returns with IRQs disabled */ return_from_SYSCALL_64: 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 /* * SYSRET can't restore RF. 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 movq RSP(%rsp), %rsp USERGS_SYSRET64 opportunistic_sysret_failed: SWAPGS jmp restore_c_regs_and_iret END(entry_SYSCALL_64) ENTRY(stub_ptregs_64) /* * Syscalls marked as needing ptregs land here. * If we are on the fast path, we need to save the extra regs, * which we achieve by trying again on the slow path. If we are on * the slow path, the extra regs are already saved. * * RAX stores a pointer to the C function implementing the syscall. * IRQs are on. */ cmpq $.Lentry_SYSCALL_64_after_fastpath_call, (%rsp) jne 1f /* * Called from fast path -- disable IRQs again, pop return address * and jump to slow path */ DISABLE_INTERRUPTS(CLBR_NONE) TRACE_IRQS_OFF popq %rax jmp entry_SYSCALL64_slow_path 1: /* Called from C */ jmp *%rax /* called from C */ END(stub_ptregs_64) .macro ptregs_stub func ENTRY(ptregs_\func) leaq \func(%rip), %rax jmp stub_ptregs_64 END(ptregs_\func) .endm /* Instantiate ptregs_stub for each ptregs-using syscall */ #define __SYSCALL_64_QUAL_(sym) #define __SYSCALL_64_QUAL_ptregs(sym) ptregs_stub sym #define __SYSCALL_64(nr, sym, qual) __SYSCALL_64_QUAL_##qual(sym) #include /* * A newly forked process directly context switches into this address. * * rdi: prev task we switched from */ ENTRY(ret_from_fork) LOCK ; btr $TIF_FORK, TI_flags(%r8) call schedule_tail /* rdi: 'prev' task parameter */ testb $3, CS(%rsp) /* from kernel_thread? */ jnz 1f /* * We came from kernel_thread. This code path is quite twisted, and * someone should clean it up. * * copy_thread_tls stashes the function pointer in RBX and the * parameter to be passed in RBP. The called function is permitted * to call do_execve and thereby jump to user mode. */ movq RBP(%rsp), %rdi call *RBX(%rsp) movl $0, RAX(%rsp) /* * Fall through as though we're exiting a syscall. This makes a * twisted sort of sense if we just called do_execve. */ 1: movq %rsp, %rdi call syscall_return_slowpath /* returns with IRQs disabled */ TRACE_IRQS_ON /* user mode is traced as IRQS on */ SWAPGS jmp restore_regs_and_iret 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 /* * 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 1: /* * 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 SWAPGS jmp restore_regs_and_iret /* Returning to kernel space */ retint_kernel: #ifdef CONFIG_PREEMPT /* Interrupts are off */ /* Check if we need preemption */ bt $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: pushq %rax pushq %rdi SWAPGS movq PER_CPU_VAR(espfix_waddr), %rdi movq %rax, (0*8)(%rdi) /* RAX */ movq (2*8)(%rsp), %rax /* RIP */ movq %rax, (1*8)(%rdi) movq (3*8)(%rsp), %rax /* CS */ movq %rax, (2*8)(%rdi) movq (4*8)(%rsp), %rax /* RFLAGS */ movq %rax, (3*8)(%rdi) movq (6*8)(%rsp), %rax /* SS */ movq %rax, (5*8)(%rdi) movq (5*8)(%rsp), %rax /* RSP */ movq %rax, (4*8)(%rdi) andl $0xffff0000, %eax popq %rdi orq PER_CPU_VAR(espfix_stack), %rax SWAPGS movq %rax, %rsp popq %rax 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 .macro apicinterrupt num sym do_sym apicinterrupt3 \num \sym \do_sym trace_apicinterrupt \num \sym .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 /* %ebx: no swapgs flag */ .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 paranoid=1 shift_ist=DEBUG_STACK 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 has_error_code=0 paranoid=1 do_sym=*machine_check_vector(%rip) #endif /* * Save all registers in pt_regs, and switch gs if needed. * Use slow, but surefire "are we in kernel?" check. * Return: ebx=0: need swapgs on exit, ebx=1: otherwise */ 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: 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 is "no swapgs" flag (1: don't need swapgs, 0: need it) */ ENTRY(paranoid_exit) DISABLE_INTERRUPTS(CLBR_NONE) TRACE_IRQS_OFF_DEBUG testl %ebx, %ebx /* swapgs needed? */ jnz paranoid_exit_no_swapgs TRACE_IRQS_IRETQ SWAPGS_UNSAFE_STACK jmp paranoid_exit_restore paranoid_exit_no_swapgs: TRACE_IRQS_IRETQ_DEBUG paranoid_exit_restore: 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. * Return: EBX=0: came from user mode; EBX=1: otherwise */ ENTRY(error_entry) cld SAVE_C_REGS 8 SAVE_EXTRA_REGS 8 xorl %ebx, %ebx testb $3, CS+8(%rsp) jz .Lerror_kernelspace .Lerror_entry_from_usermode_swapgs: /* * We entered from user mode or we're pretending to have entered * from user mode due to an IRET fault. */ SWAPGS .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: 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: incl %ebx 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 /* * 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. */ jmp .Lerror_entry_from_usermode_swapgs .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 /* * Pretend that the exception came from user mode: set up pt_regs * as if we faulted immediately after IRET and clear EBX so that * error_exit knows that we will be returning to user mode. */ mov %rsp, %rdi call fixup_bad_iret mov %rax, %rsp decl %ebx jmp .Lerror_entry_from_usermode_after_swapgs END(error_entry) /* * On entry, EBS is a "return to kernel mode" flag: * 1: already in kernel mode, don't need SWAPGS * 0: user gsbase is loaded, we need SWAPGS and standard preparation for return to usermode */ ENTRY(error_exit) movl %ebx, %eax DISABLE_INTERRUPTS(CLBR_NONE) TRACE_IRQS_OFF testl %eax, %eax jnz 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. */ /* 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 cld 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 call do_nmi /* * Return back to user mode. We must *not* do the normal exit * work, because we don't want to enable interrupts. Fortunately, * do_nmi doesn't modify pt_regs. */ 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 paranoid_entry to handle SWAPGS, but 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. */ call paranoid_entry /* paranoidentry do_nmi, 0; without TRACE_IRQS_OFF */ movq %rsp, %rdi movq $-1, %rsi call do_nmi testl %ebx, %ebx /* swapgs needed? */ jnz nmi_restore nmi_swapgs: 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)