/* SPDX-License-Identifier: GPL-2.0 */ /* * 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 #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include "calling.h" .code64 .section .entry.text, "ax" #ifdef CONFIG_PARAVIRT ENTRY(native_usergs_sysret64) UNWIND_HINT_EMPTY swapgs sysretq END(native_usergs_sysret64) #endif /* CONFIG_PARAVIRT */ .macro TRACE_IRQS_FLAGS flags:req #ifdef CONFIG_TRACE_IRQFLAGS btl $9, \flags /* interrupts off? */ jnc 1f TRACE_IRQS_ON 1: #endif .endm .macro TRACE_IRQS_IRETQ TRACE_IRQS_FLAGS EFLAGS(%rsp) .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. */ .pushsection .entry_trampoline, "ax" /* * The code in here gets remapped into cpu_entry_area's trampoline. This means * that the assembler and linker have the wrong idea as to where this code * lives (and, in fact, it's mapped more than once, so it's not even at a * fixed address). So we can't reference any symbols outside the entry * trampoline and expect it to work. * * Instead, we carefully abuse %rip-relative addressing. * _entry_trampoline(%rip) refers to the start of the remapped) entry * trampoline. We can thus find cpu_entry_area with this macro: */ #define CPU_ENTRY_AREA \ _entry_trampoline - CPU_ENTRY_AREA_entry_trampoline(%rip) /* The top word of the SYSENTER stack is hot and is usable as scratch space. */ #define RSP_SCRATCH CPU_ENTRY_AREA_entry_stack + \ SIZEOF_entry_stack - 8 + CPU_ENTRY_AREA ENTRY(entry_SYSCALL_64_trampoline) UNWIND_HINT_EMPTY swapgs /* Stash the user RSP. */ movq %rsp, RSP_SCRATCH /* Note: using %rsp as a scratch reg. */ SWITCH_TO_KERNEL_CR3 scratch_reg=%rsp /* Load the top of the task stack into RSP */ movq CPU_ENTRY_AREA_tss + TSS_sp1 + CPU_ENTRY_AREA, %rsp /* Start building the simulated IRET frame. */ pushq $__USER_DS /* pt_regs->ss */ pushq RSP_SCRATCH /* pt_regs->sp */ pushq %r11 /* pt_regs->flags */ pushq $__USER_CS /* pt_regs->cs */ pushq %rcx /* pt_regs->ip */ /* * x86 lacks a near absolute jump, and we can't jump to the real * entry text with a relative jump. We could push the target * address and then use retq, but this destroys the pipeline on * many CPUs (wasting over 20 cycles on Sandy Bridge). Instead, * spill RDI and restore it in a second-stage trampoline. */ pushq %rdi movq $entry_SYSCALL_64_stage2, %rdi JMP_NOSPEC %rdi END(entry_SYSCALL_64_trampoline) .popsection ENTRY(entry_SYSCALL_64_stage2) UNWIND_HINT_EMPTY popq %rdi jmp entry_SYSCALL_64_after_hwframe END(entry_SYSCALL_64_stage2) ENTRY(entry_SYSCALL_64) UNWIND_HINT_EMPTY /* * 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 /* * This path is only taken when PAGE_TABLE_ISOLATION is disabled so it * is not required to switch CR3. */ movq %rsp, PER_CPU_VAR(rsp_scratch) movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp /* 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 $__USER_CS /* pt_regs->cs */ pushq %rcx /* pt_regs->ip */ GLOBAL(entry_SYSCALL_64_after_hwframe) pushq %rax /* pt_regs->orig_ax */ PUSH_AND_CLEAR_REGS rax=$-ENOSYS TRACE_IRQS_OFF /* IRQs are off. */ movq %rax, %rdi movq %rsp, %rsi /* clobbers %rax, make sure it is after saving the syscall nr */ IBRS_ENTER call do_syscall_64 /* returns with IRQs disabled */ 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. If we're not, * go to the slow exit path. */ movq RCX(%rsp), %rcx movq RIP(%rsp), %r11 cmpq %rcx, %r11 /* SYSRET requires RCX == RIP */ jne swapgs_restore_regs_and_return_to_usermode /* * 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. * * Change top bits to match most significant bit (47th or 56th bit * depending on paging mode) in the address. */ #ifdef CONFIG_X86_5LEVEL ALTERNATIVE "shl $(64 - 48), %rcx; sar $(64 - 48), %rcx", \ "shl $(64 - 57), %rcx; sar $(64 - 57), %rcx", X86_FEATURE_LA57 #else shl $(64 - (__VIRTUAL_MASK_SHIFT+1)), %rcx sar $(64 - (__VIRTUAL_MASK_SHIFT+1)), %rcx #endif /* If this changed %rcx, it was not canonical */ cmpq %rcx, %r11 jne swapgs_restore_regs_and_return_to_usermode cmpq $__USER_CS, CS(%rsp) /* CS must match SYSRET */ jne swapgs_restore_regs_and_return_to_usermode movq R11(%rsp), %r11 cmpq %r11, EFLAGS(%rsp) /* R11 == RFLAGS */ jne swapgs_restore_regs_and_return_to_usermode /* * 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 swapgs_restore_regs_and_return_to_usermode /* nothing to check for RSP */ cmpq $__USER_DS, SS(%rsp) /* SS must match SYSRET */ jne swapgs_restore_regs_and_return_to_usermode /* * We win! This label is here just for ease of understanding * perf profiles. Nothing jumps here. */ syscall_return_via_sysret: IBRS_EXIT POP_REGS pop_rdi=0 /* * Now all regs are restored except RSP and RDI. * Save old stack pointer and switch to trampoline stack. */ movq %rsp, %rdi movq PER_CPU_VAR(cpu_tss_rw + TSS_sp0), %rsp UNWIND_HINT_EMPTY pushq RSP-RDI(%rdi) /* RSP */ pushq (%rdi) /* RDI */ /* * We are on the trampoline stack. All regs except RDI are live. * We can do future final exit work right here. */ SWITCH_TO_USER_CR3_STACK scratch_reg=%rdi popq %rdi popq %rsp USERGS_SYSRET64 END(entry_SYSCALL_64) /* * %rdi: prev task * %rsi: next task */ ENTRY(__switch_to_asm) UNWIND_HINT_FUNC /* * 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_STACKPROTECTOR movq TASK_stack_canary(%rsi), %rbx movq %rbx, PER_CPU_VAR(irq_stack_union)+stack_canary_offset #endif /* * 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 /* 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) UNWIND_HINT_EMPTY movq %rax, %rdi call schedule_tail /* rdi: 'prev' task parameter */ testq %rbx, %rbx /* from kernel_thread? */ jnz 1f /* kernel threads are uncommon */ 2: UNWIND_HINT_REGS movq %rsp, %rdi call syscall_return_slowpath /* returns with IRQs disabled */ TRACE_IRQS_ON /* user mode is traced as IRQS on */ jmp swapgs_restore_regs_and_return_to_usermode 1: /* kernel thread */ UNWIND_HINT_EMPTY 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) UNWIND_HINT_IRET_REGS pushq $(~vector+0x80) /* Note: always in signed byte range */ jmp common_interrupt .align 8 vector=vector+1 .endr END(irq_entries_start) .align 8 ENTRY(spurious_entries_start) vector=FIRST_SYSTEM_VECTOR .rept (NR_VECTORS - FIRST_SYSTEM_VECTOR) UNWIND_HINT_IRET_REGS pushq $(~vector+0x80) /* Note: always in signed byte range */ jmp common_spurious .align 8 vector=vector+1 .endr END(spurious_entries_start) .macro DEBUG_ENTRY_ASSERT_IRQS_OFF #ifdef CONFIG_DEBUG_ENTRY pushq %rax SAVE_FLAGS(CLBR_RAX) testl $X86_EFLAGS_IF, %eax jz .Lokay_\@ ud2 .Lokay_\@: popq %rax #endif .endm /* * Enters the IRQ stack if we're not already using it. NMI-safe. Clobbers * flags and puts old RSP into old_rsp, and leaves all other GPRs alone. * Requires kernel GSBASE. * * The invariant is that, if irq_count != -1, then the IRQ stack is in use. */ .macro ENTER_IRQ_STACK regs=1 old_rsp save_ret=0 DEBUG_ENTRY_ASSERT_IRQS_OFF .if \save_ret /* * If save_ret is set, the original stack contains one additional * entry -- the return address. Therefore, move the address one * entry below %rsp to \old_rsp. */ leaq 8(%rsp), \old_rsp .else movq %rsp, \old_rsp .endif .if \regs UNWIND_HINT_REGS base=\old_rsp .endif incl PER_CPU_VAR(irq_count) jnz .Lirq_stack_push_old_rsp_\@ /* * Right now, if we just incremented irq_count to zero, we've * claimed the IRQ stack but we haven't switched to it yet. * * If anything is added that can interrupt us here without using IST, * it must be *extremely* careful to limit its stack usage. This * could include kprobes and a hypothetical future IST-less #DB * handler. * * The OOPS unwinder relies on the word at the top of the IRQ * stack linking back to the previous RSP for the entire time we're * on the IRQ stack. For this to work reliably, we need to write * it before we actually move ourselves to the IRQ stack. */ movq \old_rsp, PER_CPU_VAR(irq_stack_union + IRQ_STACK_SIZE - 8) movq PER_CPU_VAR(irq_stack_ptr), %rsp #ifdef CONFIG_DEBUG_ENTRY /* * If the first movq above becomes wrong due to IRQ stack layout * changes, the only way we'll notice is if we try to unwind right * here. Assert that we set up the stack right to catch this type * of bug quickly. */ cmpq -8(%rsp), \old_rsp je .Lirq_stack_okay\@ ud2 .Lirq_stack_okay\@: #endif .Lirq_stack_push_old_rsp_\@: pushq \old_rsp .if \regs UNWIND_HINT_REGS indirect=1 .endif .if \save_ret /* * Push the return address to the stack. This return address can * be found at the "real" original RSP, which was offset by 8 at * the beginning of this macro. */ pushq -8(\old_rsp) .endif .endm /* * Undoes ENTER_IRQ_STACK. */ .macro LEAVE_IRQ_STACK regs=1 DEBUG_ENTRY_ASSERT_IRQS_OFF /* We need to be off the IRQ stack before decrementing irq_count. */ popq %rsp .if \regs UNWIND_HINT_REGS .endif /* * As in ENTER_IRQ_STACK, irq_count == 0, we are still claiming * the irq stack but we're not on it. */ decl PER_CPU_VAR(irq_count) .endm /* * Interrupt entry helper function. * * Entry runs with interrupts off. Stack layout at entry: * +----------------------------------------------------+ * | regs->ss | * | regs->rsp | * | regs->eflags | * | regs->cs | * | regs->ip | * +----------------------------------------------------+ * | regs->orig_ax = ~(interrupt number) | * +----------------------------------------------------+ * | return address | * +----------------------------------------------------+ */ ENTRY(interrupt_entry) UNWIND_HINT_IRET_REGS offset=16 ASM_CLAC cld testb $3, CS-ORIG_RAX+8(%rsp) jz 1f SWAPGS FENCE_SWAPGS_USER_ENTRY /* * Switch to the thread stack. The IRET frame and orig_ax are * on the stack, as well as the return address. RDI..R12 are * not (yet) on the stack and space has not (yet) been * allocated for them. */ pushq %rdi /* Need to switch before accessing the thread stack. */ SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi movq %rsp, %rdi movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp /* * We have RDI, return address, and orig_ax on the stack on * top of the IRET frame. That means offset=24 */ UNWIND_HINT_IRET_REGS base=%rdi offset=24 pushq 7*8(%rdi) /* regs->ss */ pushq 6*8(%rdi) /* regs->rsp */ pushq 5*8(%rdi) /* regs->eflags */ pushq 4*8(%rdi) /* regs->cs */ pushq 3*8(%rdi) /* regs->ip */ UNWIND_HINT_IRET_REGS pushq 2*8(%rdi) /* regs->orig_ax */ pushq 8(%rdi) /* return address */ movq (%rdi), %rdi jmp 2f 1: FENCE_SWAPGS_KERNEL_ENTRY 2: PUSH_AND_CLEAR_REGS save_ret=1 ENCODE_FRAME_POINTER 8 testb $3, CS+8(%rsp) jz 1f /* * IRQ from user mode. * * 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 is 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: ENTER_IRQ_STACK old_rsp=%rdi save_ret=1 /* We entered an interrupt context - irqs are off: */ TRACE_IRQS_OFF ret END(interrupt_entry) _ASM_NOKPROBE(interrupt_entry) /* Interrupt entry/exit. */ /* * The interrupt stubs push (~vector+0x80) onto the stack and * then jump to common_spurious/interrupt. */ common_spurious: addq $-0x80, (%rsp) /* Adjust vector to [-256, -1] range */ call interrupt_entry UNWIND_HINT_REGS indirect=1 call smp_spurious_interrupt /* rdi points to pt_regs */ jmp ret_from_intr END(common_spurious) _ASM_NOKPROBE(common_spurious) /* common_interrupt is a hotpath. Align it */ .p2align CONFIG_X86_L1_CACHE_SHIFT common_interrupt: addq $-0x80, (%rsp) /* Adjust vector to [-256, -1] range */ call interrupt_entry UNWIND_HINT_REGS indirect=1 call do_IRQ /* rdi points to pt_regs */ /* 0(%rsp): old RSP */ ret_from_intr: DISABLE_INTERRUPTS(CLBR_ANY) TRACE_IRQS_OFF LEAVE_IRQ_STACK 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 GLOBAL(swapgs_restore_regs_and_return_to_usermode) IBRS_EXIT #ifdef CONFIG_DEBUG_ENTRY /* Assert that pt_regs indicates user mode. */ testb $3, CS(%rsp) jnz 1f ud2 1: #endif POP_REGS pop_rdi=0 /* * The stack is now user RDI, orig_ax, RIP, CS, EFLAGS, RSP, SS. * Save old stack pointer and switch to trampoline stack. */ movq %rsp, %rdi movq PER_CPU_VAR(cpu_tss_rw + TSS_sp0), %rsp UNWIND_HINT_EMPTY /* Copy the IRET frame to the trampoline stack. */ pushq 6*8(%rdi) /* SS */ pushq 5*8(%rdi) /* RSP */ pushq 4*8(%rdi) /* EFLAGS */ pushq 3*8(%rdi) /* CS */ pushq 2*8(%rdi) /* RIP */ /* Push user RDI on the trampoline stack. */ pushq (%rdi) /* * We are on the trampoline stack. All regs except RDI are live. * We can do future final exit work right here. */ SWITCH_TO_USER_CR3_STACK scratch_reg=%rdi /* Restore RDI. */ popq %rdi SWAPGS INTERRUPT_RETURN /* 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 GLOBAL(restore_regs_and_return_to_kernel) #ifdef CONFIG_DEBUG_ENTRY /* Assert that pt_regs indicates kernel mode. */ testb $3, CS(%rsp) jz 1f ud2 1: #endif POP_REGS addq $8, %rsp /* skip regs->orig_ax */ /* * ARCH_HAS_MEMBARRIER_SYNC_CORE rely on IRET core serialization * when returning from IPI handler. */ INTERRUPT_RETURN ENTRY(native_iret) UNWIND_HINT_IRET_REGS /* * 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 /* to kernel GS */ SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi /* to 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) */ /* * 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_TO_USER_CR3_STACK scratch_reg=%rdi SWAPGS /* to user GS */ popq %rdi /* Restore user RDI */ movq %rax, %rsp UNWIND_HINT_IRET_REGS offset=8 /* * 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) _ASM_NOKPROBE(common_interrupt) /* * APIC interrupts. */ .macro apicinterrupt3 num sym do_sym ENTRY(\sym) UNWIND_HINT_IRET_REGS pushq $~(\num) .Lcommon_\sym: call interrupt_entry UNWIND_HINT_REGS indirect=1 call \do_sym /* rdi points to pt_regs */ jmp ret_from_intr END(\sym) _ASM_NOKPROBE(\sym) .endm /* 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 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 apicinterrupt3 POSTED_INTR_NESTED_VECTOR kvm_posted_intr_nested_ipi smp_kvm_posted_intr_nested_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_rw) + (TSS_ist + ((x) - 1) * 8) .macro idtentry sym do_sym has_error_code:req paranoid=0 shift_ist=-1 create_gap=0 ENTRY(\sym) UNWIND_HINT_IRET_REGS offset=\has_error_code*8 /* Sanity check */ .if \shift_ist != -1 && \paranoid == 0 .error "using shift_ist requires paranoid=1" .endif ASM_CLAC .if \has_error_code == 0 pushq $-1 /* ORIG_RAX: no syscall to restart */ .endif .if \paranoid == 1 testb $3, CS-ORIG_RAX(%rsp) /* If coming from userspace, switch stacks */ jnz .Lfrom_usermode_switch_stack_\@ .endif .if \create_gap == 1 /* * If coming from kernel space, create a 6-word gap to allow the * int3 handler to emulate a call instruction. */ testb $3, CS-ORIG_RAX(%rsp) jnz .Lfrom_usermode_no_gap_\@ .rept 6 pushq 5*8(%rsp) .endr UNWIND_HINT_IRET_REGS offset=8 .Lfrom_usermode_no_gap_\@: .endif .if \paranoid call paranoid_entry .else call error_entry .endif UNWIND_HINT_REGS /* 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 /* * 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). */ .Lfrom_usermode_switch_stack_\@: call error_entry 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 _ASM_NOKPROBE(\sym) END(\sym) .endm 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) FRAME_BEGIN pushfq DISABLE_INTERRUPTS(CLBR_ANY & ~CLBR_RDI) TRACE_IRQS_OFF SWAPGS .Lgs_change: movl %edi, %gs 2: ALTERNATIVE "", "mfence", X86_BUG_SWAPGS_FENCE SWAPGS TRACE_IRQS_FLAGS (%rsp) popfq FRAME_END ret ENDPROC(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 ENTER_IRQ_STACK regs=0 old_rsp=%r11 call __do_softirq LEAVE_IRQ_STACK regs=0 leaveq ret ENDPROC(do_softirq_own_stack) #ifdef CONFIG_XEN idtentry 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 */ UNWIND_HINT_FUNC movq %rdi, %rsp /* we don't return, adjust the stack frame */ UNWIND_HINT_REGS ENTER_IRQ_STACK old_rsp=%r10 call xen_evtchn_do_upcall LEAVE_IRQ_STACK #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) UNWIND_HINT_EMPTY 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 */ UNWIND_HINT_IRET_REGS offset=8 jmp general_protection 1: /* Segment mismatch => Category 1 (Bad segment). Retry the IRET. */ movq (%rsp), %rcx movq 8(%rsp), %r11 addq $0x30, %rsp UNWIND_HINT_IRET_REGS pushq $-1 /* orig_ax = -1 => not a system call */ PUSH_AND_CLEAR_REGS ENCODE_FRAME_POINTER 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 apicinterrupt3 HYPERV_REENLIGHTENMENT_VECTOR \ hyperv_reenlightenment_vector hyperv_reenlightenment_intr apicinterrupt3 HYPERV_STIMER0_VECTOR \ hv_stimer0_callback_vector hv_stimer0_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 create_gap=1 idtentry stack_segment do_stack_segment has_error_code=1 #ifdef CONFIG_XEN idtentry xennmi do_nmi has_error_code=0 idtentry xendebug do_debug has_error_code=0 #endif idtentry general_protection do_general_protection has_error_code=1 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: need swapgs on exit, ebx=1: otherwise */ ENTRY(paranoid_entry) UNWIND_HINT_FUNC cld PUSH_AND_CLEAR_REGS save_ret=1 ENCODE_FRAME_POINTER 8 movl $1, %ebx movl $MSR_GS_BASE, %ecx rdmsr testl %edx, %edx js 1f /* negative -> in kernel */ SWAPGS xorl %ebx, %ebx 1: /* * Always stash CR3 in %r14. This value will be restored, * verbatim, at exit. Needed if paranoid_entry interrupted * another entry that already switched to the user CR3 value * but has not yet returned to userspace. * * This is also why CS (stashed in the "iret frame" by the * hardware at entry) can not be used: this may be a return * to kernel code, but with a user CR3 value. */ SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg=%rax save_reg=%r14 /* * The above SAVE_AND_SWITCH_TO_KERNEL_CR3 macro 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 /* * Once we have CR3 and %GS setup save and set SPEC_CTRL. Just like * CR3 above, keep the old value in a callee saved register. */ IBRS_ENTER save_reg=%r15 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) UNWIND_HINT_REGS DISABLE_INTERRUPTS(CLBR_ANY) TRACE_IRQS_OFF_DEBUG testl %ebx, %ebx /* swapgs needed? */ jnz .Lparanoid_exit_no_swapgs TRACE_IRQS_IRETQ /* Always restore stashed CR3 value (see paranoid_entry) */ RESTORE_CR3 scratch_reg=%rbx save_reg=%r14 SWAPGS_UNSAFE_STACK jmp .Lparanoid_exit_restore .Lparanoid_exit_no_swapgs: TRACE_IRQS_IRETQ_DEBUG /* * Must restore IBRS state before both CR3 and %GS since we need access * to the per-CPU x86_spec_ctrl_shadow variable. */ IBRS_EXIT save_reg=%r15 /* Always restore stashed CR3 value (see paranoid_entry) */ RESTORE_CR3 scratch_reg=%rbx save_reg=%r14 .Lparanoid_exit_restore: jmp restore_regs_and_return_to_kernel END(paranoid_exit) /* * Save all registers in pt_regs, and switch GS if needed. */ ENTRY(error_entry) UNWIND_HINT_FUNC cld PUSH_AND_CLEAR_REGS save_ret=1 ENCODE_FRAME_POINTER 8 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 /* We have user CR3. Change to kernel CR3. */ SWITCH_TO_KERNEL_CR3 scratch_reg=%rax IBRS_ENTER .Lerror_entry_from_usermode_after_swapgs: /* Put us onto the real thread stack. */ popq %r12 /* save return addr in %12 */ movq %rsp, %rdi /* arg0 = pt_regs pointer */ call sync_regs movq %rax, %rsp /* switch stack */ ENCODE_FRAME_POINTER pushq %r12 /* * 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 SWITCH_TO_KERNEL_CR3 scratch_reg=%rax 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 and CR3. Switch to kernel gsbase and CR3: */ SWAPGS FENCE_SWAPGS_USER_ENTRY SWITCH_TO_KERNEL_CR3 scratch_reg=%rax IBRS_ENTER /* * 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) UNWIND_HINT_REGS DISABLE_INTERRUPTS(CLBR_ANY) TRACE_IRQS_OFF testb $3, CS(%rsp) jz retint_kernel jmp retint_user END(error_exit) /* * Runs on exception stack. Xen PV does not go through this path at all, * so we can use real assembly here. * * Registers: * %r14: Used to save/restore the CR3 of the interrupted context * when PAGE_TABLE_ISOLATION is in use. Do not clobber. */ ENTRY(nmi) UNWIND_HINT_IRET_REGS /* * 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 cld FENCE_SWAPGS_USER_ENTRY SWITCH_TO_KERNEL_CR3 scratch_reg=%rdx movq %rsp, %rdx movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp UNWIND_HINT_IRET_REGS base=%rdx offset=8 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 */ UNWIND_HINT_IRET_REGS pushq $-1 /* pt_regs->orig_ax */ PUSH_AND_CLEAR_REGS rdx=(%rdx) ENCODE_FRAME_POINTER IBRS_ENTER /* * 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. */ jmp swapgs_restore_regs_and_return_to_usermode .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. */ iretq 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 UNWIND_HINT_IRET_REGS /* 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 */ iretq /* continues at repeat_nmi below */ UNWIND_HINT_IRET_REGS 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 */ /* * 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 UNWIND_HINT_REGS /* paranoidentry do_nmi, 0; without TRACE_IRQS_OFF */ movq %rsp, %rdi movq $-1, %rsi call do_nmi /* Always restore stashed SPEC_CTRL value (see paranoid_entry) */ IBRS_EXIT save_reg=%r15 /* Always restore stashed CR3 value (see paranoid_entry) */ RESTORE_CR3 scratch_reg=%r15 save_reg=%r14 testl %ebx, %ebx /* swapgs needed? */ jnz nmi_restore nmi_swapgs: SWAPGS_UNSAFE_STACK nmi_restore: POP_REGS /* * Skip orig_ax and the "outermost" frame to point RSP at the "iret" * at the "iret" frame. */ addq $6*8, %rsp /* * 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. * * We arguably should just inspect RIP instead, but I (Andy) wrote * this code when I had the misapprehension that Xen PV supported * NMIs, and Xen PV would break that approach. */ std movq $0, 5*8(%rsp) /* clear "NMI executing" */ /* * iretq 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. Similarly, we don't need to worry * about espfix64 on the way back to kernel mode. */ iretq END(nmi) ENTRY(ignore_sysret) UNWIND_HINT_EMPTY mov $-ENOSYS, %eax sysret END(ignore_sysret) ENTRY(rewind_stack_do_exit) UNWIND_HINT_FUNC /* 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 -PTREGS_SIZE(%rax), %rsp UNWIND_HINT_REGS call do_exit END(rewind_stack_do_exit)