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Diffstat (limited to 'arch/x86/entry/entry_64.S')
| -rw-r--r-- | arch/x86/entry/entry_64.S | 1523 |
1 files changed, 1523 insertions, 0 deletions
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S new file mode 100644 index 000000000..23212c53c --- /dev/null +++ b/arch/x86/entry/entry_64.S @@ -0,0 +1,1523 @@ +/* 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 <pavel@suse.cz> + * + * entry.S contains the system-call and fault low-level handling routines. + * + * Some of this is documented in Documentation/x86/entry_64.rst + * + * 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: + * - SYM_FUNC_START/END:Define functions in the symbol table. + * - idtentry: Define exception entry points. + */ +#include <linux/linkage.h> +#include <asm/segment.h> +#include <asm/cache.h> +#include <asm/errno.h> +#include <asm/asm-offsets.h> +#include <asm/msr.h> +#include <asm/unistd.h> +#include <asm/thread_info.h> +#include <asm/hw_irq.h> +#include <asm/page_types.h> +#include <asm/irqflags.h> +#include <asm/paravirt.h> +#include <asm/percpu.h> +#include <asm/asm.h> +#include <asm/smap.h> +#include <asm/pgtable_types.h> +#include <asm/export.h> +#include <asm/frame.h> +#include <asm/trapnr.h> +#include <asm/nospec-branch.h> +#include <asm/fsgsbase.h> +#include <linux/err.h> + +#include "calling.h" + +.code64 +.section .entry.text, "ax" + +#ifdef CONFIG_PARAVIRT_XXL +SYM_CODE_START(native_usergs_sysret64) + UNWIND_HINT_EMPTY + swapgs + sysretq +SYM_CODE_END(native_usergs_sysret64) +#endif /* CONFIG_PARAVIRT_XXL */ + +/* + * 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. + */ + +SYM_CODE_START(entry_SYSCALL_64) + UNWIND_HINT_ENTRY + + swapgs + /* tss.sp2 is scratch space. */ + movq %rsp, PER_CPU_VAR(cpu_tss_rw + TSS_sp2) + SWITCH_TO_KERNEL_CR3 scratch_reg=%rsp + movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp + +SYM_INNER_LABEL(entry_SYSCALL_64_safe_stack, SYM_L_GLOBAL) + + /* Construct struct pt_regs on stack */ + pushq $__USER_DS /* pt_regs->ss */ + pushq PER_CPU_VAR(cpu_tss_rw + TSS_sp2) /* pt_regs->sp */ + pushq %r11 /* pt_regs->flags */ + pushq $__USER_CS /* pt_regs->cs */ + pushq %rcx /* pt_regs->ip */ +SYM_INNER_LABEL(entry_SYSCALL_64_after_hwframe, SYM_L_GLOBAL) + pushq %rax /* pt_regs->orig_ax */ + + PUSH_AND_CLEAR_REGS rax=$-ENOSYS + + /* IRQs are off. */ + movq %rax, %rdi + movq %rsp, %rsi + + /* clobbers %rax, make sure it is after saving the syscall nr */ + IBRS_ENTER + UNTRAIN_RET + + call do_syscall_64 /* returns with IRQs disabled */ + + /* + * 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. + */ + STACKLEAK_ERASE_NOCLOBBER + + SWITCH_TO_USER_CR3_STACK scratch_reg=%rdi + + popq %rdi + popq %rsp + USERGS_SYSRET64 +SYM_CODE_END(entry_SYSCALL_64) + +/* + * %rdi: prev task + * %rsi: next task + */ +.pushsection .text, "ax" +SYM_FUNC_START(__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 + + /* 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(fixed_percpu_data) + 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 */ + popq %r15 + popq %r14 + popq %r13 + popq %r12 + popq %rbx + popq %rbp + + jmp __switch_to +SYM_FUNC_END(__switch_to_asm) +.popsection + +/* + * 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 + */ +.pushsection .text, "ax" +SYM_CODE_START(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_exit_to_user_mode /* returns with IRQs disabled */ + 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 kernel_execve(). Exit to userspace to complete the execve() + * syscall. + */ + movq $0, RAX(%rsp) + jmp 2b +SYM_CODE_END(ret_from_fork) +.popsection + +.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 + +/** + * idtentry_body - Macro to emit code calling the C function + * @cfunc: C function to be called + * @has_error_code: Hardware pushed error code on stack + */ +.macro idtentry_body cfunc has_error_code:req + + call error_entry + UNWIND_HINT_REGS + + movq %rsp, %rdi /* pt_regs pointer into 1st argument*/ + + .if \has_error_code == 1 + movq ORIG_RAX(%rsp), %rsi /* get error code into 2nd argument*/ + movq $-1, ORIG_RAX(%rsp) /* no syscall to restart */ + .endif + + call \cfunc + + jmp error_return +.endm + +/** + * idtentry - Macro to generate entry stubs for simple IDT entries + * @vector: Vector number + * @asmsym: ASM symbol for the entry point + * @cfunc: C function to be called + * @has_error_code: Hardware pushed error code on stack + * + * The macro emits code to set up the kernel context for straight forward + * and simple IDT entries. No IST stack, no paranoid entry checks. + */ +.macro idtentry vector asmsym cfunc has_error_code:req +SYM_CODE_START(\asmsym) + UNWIND_HINT_IRET_REGS offset=\has_error_code*8 + ASM_CLAC + + .if \has_error_code == 0 + pushq $-1 /* ORIG_RAX: no syscall to restart */ + .endif + + .if \vector == X86_TRAP_BP + /* + * 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 + + idtentry_body \cfunc \has_error_code + +_ASM_NOKPROBE(\asmsym) +SYM_CODE_END(\asmsym) +.endm + +/* + * Interrupt entry/exit. + * + + The interrupt stubs push (vector) onto the stack, which is the error_code + * position of idtentry exceptions, and jump to one of the two idtentry points + * (common/spurious). + * + * common_interrupt is a hotpath, align it to a cache line + */ +.macro idtentry_irq vector cfunc + .p2align CONFIG_X86_L1_CACHE_SHIFT + idtentry \vector asm_\cfunc \cfunc has_error_code=1 +.endm + +/* + * System vectors which invoke their handlers directly and are not + * going through the regular common device interrupt handling code. + */ +.macro idtentry_sysvec vector cfunc + idtentry \vector asm_\cfunc \cfunc has_error_code=0 +.endm + +/** + * idtentry_mce_db - Macro to generate entry stubs for #MC and #DB + * @vector: Vector number + * @asmsym: ASM symbol for the entry point + * @cfunc: C function to be called + * + * The macro emits code to set up the kernel context for #MC and #DB + * + * If the entry comes from user space it uses the normal entry path + * including the return to user space work and preemption checks on + * exit. + * + * If hits in kernel mode then it needs to go through the paranoid + * entry as the exception can hit any random state. No preemption + * check on exit to keep the paranoid path simple. + */ +.macro idtentry_mce_db vector asmsym cfunc +SYM_CODE_START(\asmsym) + UNWIND_HINT_IRET_REGS + ASM_CLAC + + pushq $-1 /* ORIG_RAX: no syscall to restart */ + + /* + * If the entry is from userspace, switch stacks and treat it as + * a normal entry. + */ + testb $3, CS-ORIG_RAX(%rsp) + jnz .Lfrom_usermode_switch_stack_\@ + + /* paranoid_entry returns GS information for paranoid_exit in EBX. */ + call paranoid_entry + + UNWIND_HINT_REGS + + movq %rsp, %rdi /* pt_regs pointer */ + + call \cfunc + + jmp paranoid_exit + + /* Switch to the regular task stack and use the noist entry point */ +.Lfrom_usermode_switch_stack_\@: + idtentry_body noist_\cfunc, has_error_code=0 + +_ASM_NOKPROBE(\asmsym) +SYM_CODE_END(\asmsym) +.endm + +#ifdef CONFIG_AMD_MEM_ENCRYPT +/** + * idtentry_vc - Macro to generate entry stub for #VC + * @vector: Vector number + * @asmsym: ASM symbol for the entry point + * @cfunc: C function to be called + * + * The macro emits code to set up the kernel context for #VC. The #VC handler + * runs on an IST stack and needs to be able to cause nested #VC exceptions. + * + * To make this work the #VC entry code tries its best to pretend it doesn't use + * an IST stack by switching to the task stack if coming from user-space (which + * includes early SYSCALL entry path) or back to the stack in the IRET frame if + * entered from kernel-mode. + * + * If entered from kernel-mode the return stack is validated first, and if it is + * not safe to use (e.g. because it points to the entry stack) the #VC handler + * will switch to a fall-back stack (VC2) and call a special handler function. + * + * The macro is only used for one vector, but it is planned to be extended in + * the future for the #HV exception. + */ +.macro idtentry_vc vector asmsym cfunc +SYM_CODE_START(\asmsym) + UNWIND_HINT_IRET_REGS + ASM_CLAC + + /* + * If the entry is from userspace, switch stacks and treat it as + * a normal entry. + */ + testb $3, CS-ORIG_RAX(%rsp) + jnz .Lfrom_usermode_switch_stack_\@ + + /* + * paranoid_entry returns SWAPGS flag for paranoid_exit in EBX. + * EBX == 0 -> SWAPGS, EBX == 1 -> no SWAPGS + */ + call paranoid_entry + + UNWIND_HINT_REGS + + /* + * Switch off the IST stack to make it free for nested exceptions. The + * vc_switch_off_ist() function will switch back to the interrupted + * stack if it is safe to do so. If not it switches to the VC fall-back + * stack. + */ + movq %rsp, %rdi /* pt_regs pointer */ + call vc_switch_off_ist + movq %rax, %rsp /* Switch to new stack */ + + ENCODE_FRAME_POINTER + UNWIND_HINT_REGS + + /* Update pt_regs */ + movq ORIG_RAX(%rsp), %rsi /* get error code into 2nd argument*/ + movq $-1, ORIG_RAX(%rsp) /* no syscall to restart */ + + movq %rsp, %rdi /* pt_regs pointer */ + + call kernel_\cfunc + + /* + * No need to switch back to the IST stack. The current stack is either + * identical to the stack in the IRET frame or the VC fall-back stack, + * so it is definitly mapped even with PTI enabled. + */ + jmp paranoid_exit + + /* Switch to the regular task stack */ +.Lfrom_usermode_switch_stack_\@: + idtentry_body user_\cfunc, has_error_code=1 + +_ASM_NOKPROBE(\asmsym) +SYM_CODE_END(\asmsym) +.endm +#endif + +/* + * Double fault entry. Straight paranoid. No checks from which context + * this comes because for the espfix induced #DF this would do the wrong + * thing. + */ +.macro idtentry_df vector asmsym cfunc +SYM_CODE_START(\asmsym) + UNWIND_HINT_IRET_REGS offset=8 + ASM_CLAC + + /* paranoid_entry returns GS information for paranoid_exit in EBX. */ + call paranoid_entry + UNWIND_HINT_REGS + + movq %rsp, %rdi /* pt_regs pointer into first argument */ + movq ORIG_RAX(%rsp), %rsi /* get error code into 2nd argument*/ + movq $-1, ORIG_RAX(%rsp) /* no syscall to restart */ + call \cfunc + + jmp paranoid_exit + +_ASM_NOKPROBE(\asmsym) +SYM_CODE_END(\asmsym) +.endm + +/* + * Include the defines which emit the idt entries which are shared + * shared between 32 and 64 bit and emit the __irqentry_text_* markers + * so the stacktrace boundary checks work. + */ + .align 16 + .globl __irqentry_text_start +__irqentry_text_start: + +#include <asm/idtentry.h> + + .align 16 + .globl __irqentry_text_end +__irqentry_text_end: + +SYM_CODE_START_LOCAL(common_interrupt_return) +SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL) + IBRS_EXIT +#ifdef CONFIG_DEBUG_ENTRY + /* Assert that pt_regs indicates user mode. */ + testb $3, CS(%rsp) + jnz 1f + ud2 +1: +#endif +#ifdef CONFIG_XEN_PV + ALTERNATIVE "", "jmp xenpv_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV +#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. + */ + STACKLEAK_ERASE_NOCLOBBER + + SWITCH_TO_USER_CR3_STACK scratch_reg=%rdi + + /* Restore RDI. */ + popq %rdi + SWAPGS + INTERRUPT_RETURN + + +SYM_INNER_LABEL(restore_regs_and_return_to_kernel, SYM_L_GLOBAL) +#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 + +SYM_INNER_LABEL_ALIGN(native_iret, SYM_L_GLOBAL) + 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 + +SYM_INNER_LABEL(native_irq_return_iret, SYM_L_GLOBAL) + /* + * 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 exc_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 */ + UNTRAIN_RET + + 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 +SYM_CODE_END(common_interrupt_return) +_ASM_NOKPROBE(common_interrupt_return) + +/* + * Reload gs selector with exception handling + * edi: new selector + * + * Is in entry.text as it shouldn't be instrumented. + */ +SYM_FUNC_START(asm_load_gs_index) + FRAME_BEGIN + swapgs +.Lgs_change: + movl %edi, %gs +2: ALTERNATIVE "", "mfence", X86_BUG_SWAPGS_FENCE + swapgs + FRAME_END + RET +SYM_FUNC_END(asm_load_gs_index) +EXPORT_SYMBOL(asm_load_gs_index) + + _ASM_EXTABLE(.Lgs_change, .Lbad_gs) + .section .fixup, "ax" + /* running with kernelgs */ +SYM_CODE_START_LOCAL_NOALIGN(.Lbad_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 +SYM_CODE_END(.Lbad_gs) + .previous + +/* + * rdi: New stack pointer points to the top word of the stack + * rsi: Function pointer + * rdx: Function argument (can be NULL if none) + */ +SYM_FUNC_START(asm_call_on_stack) +SYM_INNER_LABEL(asm_call_sysvec_on_stack, SYM_L_GLOBAL) +SYM_INNER_LABEL(asm_call_irq_on_stack, SYM_L_GLOBAL) + /* + * Save the frame pointer unconditionally. This allows the ORC + * unwinder to handle the stack switch. + */ + pushq %rbp + mov %rsp, %rbp + + /* + * The unwinder relies on the word at the top of the new stack + * page linking back to the previous RSP. + */ + mov %rsp, (%rdi) + mov %rdi, %rsp + /* Move the argument to the right place */ + mov %rdx, %rdi + +1: + .pushsection .discard.instr_begin + .long 1b - . + .popsection + + CALL_NOSPEC rsi + +2: + .pushsection .discard.instr_end + .long 2b - . + .popsection + + /* Restore the previous stack pointer from RBP. */ + leaveq + RET +SYM_FUNC_END(asm_call_on_stack) + +#ifdef CONFIG_XEN_PV +/* + * 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. + * + * C calling convention: exc_xen_hypervisor_callback(struct *pt_regs) + */ +SYM_CODE_START_LOCAL(exc_xen_hypervisor_callback) + +/* + * 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 + + call xen_pv_evtchn_do_upcall + + jmp error_return +SYM_CODE_END(exc_xen_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. + */ +SYM_CODE_START(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 asm_exc_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_return +SYM_CODE_END(xen_failsafe_callback) +#endif /* CONFIG_XEN_PV */ + +/* + * Save all registers in pt_regs. Return GSBASE related information + * in EBX depending on the availability of the FSGSBASE instructions: + * + * FSGSBASE R/EBX + * N 0 -> SWAPGS on exit + * 1 -> no SWAPGS on exit + * + * Y GSBASE value at entry, must be restored in paranoid_exit + * + * R14 - old CR3 + * R15 - old SPEC_CTRL + */ +SYM_CODE_START_LOCAL(paranoid_entry) + UNWIND_HINT_FUNC + cld + PUSH_AND_CLEAR_REGS save_ret=1 + ENCODE_FRAME_POINTER 8 + + /* + * 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. + * + * Switching CR3 does not depend on kernel GSBASE so it can + * be done before switching to the kernel GSBASE. This is + * required for FSGSBASE because the kernel GSBASE has to + * be retrieved from a kernel internal table. + */ + SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg=%rax save_reg=%r14 + + /* + * Handling GSBASE depends on the availability of FSGSBASE. + * + * Without FSGSBASE the kernel enforces that negative GSBASE + * values indicate kernel GSBASE. With FSGSBASE no assumptions + * can be made about the GSBASE value when entering from user + * space. + */ + ALTERNATIVE "jmp .Lparanoid_entry_checkgs", "", X86_FEATURE_FSGSBASE + + /* + * Read the current GSBASE and store it in %rbx unconditionally, + * retrieve and set the current CPUs kernel GSBASE. The stored value + * has to be restored in paranoid_exit unconditionally. + * + * The unconditional write to GS base below ensures that no subsequent + * loads based on a mispredicted GS base can happen, therefore no LFENCE + * is needed here. + */ + SAVE_AND_SET_GSBASE scratch_reg=%rax save_reg=%rbx + jmp .Lparanoid_gsbase_done + +.Lparanoid_entry_checkgs: + /* EBX = 1 -> kernel GSBASE active, no restore required */ + movl $1, %ebx + + /* + * The kernel-enforced convention is a negative GSBASE indicates + * a kernel value. No SWAPGS needed on entry and exit. + */ + movl $MSR_GS_BASE, %ecx + rdmsr + testl %edx, %edx + js .Lparanoid_kernel_gsbase + + /* EBX = 0 -> SWAPGS required on exit */ + xorl %ebx, %ebx + swapgs +.Lparanoid_kernel_gsbase: + FENCE_SWAPGS_KERNEL_ENTRY +.Lparanoid_gsbase_done: + + /* + * 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 + UNTRAIN_RET + + RET +SYM_CODE_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, there's no good reason to try + * to handle preemption here. + * + * R/EBX contains the GSBASE related information depending on the + * availability of the FSGSBASE instructions: + * + * FSGSBASE R/EBX + * N 0 -> SWAPGS on exit + * 1 -> no SWAPGS on exit + * + * Y User space GSBASE, must be restored unconditionally + * + * R14 - old CR3 + * R15 - old SPEC_CTRL + */ +SYM_CODE_START_LOCAL(paranoid_exit) + UNWIND_HINT_REGS + + /* + * 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 + + /* + * The order of operations is important. RESTORE_CR3 requires + * kernel GSBASE. + * + * NB to anyone to try to optimize this code: this code does + * not execute at all for exceptions from user mode. Those + * exceptions go through error_exit instead. + */ + RESTORE_CR3 scratch_reg=%rax save_reg=%r14 + + /* Handle the three GSBASE cases */ + ALTERNATIVE "jmp .Lparanoid_exit_checkgs", "", X86_FEATURE_FSGSBASE + + /* With FSGSBASE enabled, unconditionally restore GSBASE */ + wrgsbase %rbx + jmp restore_regs_and_return_to_kernel + +.Lparanoid_exit_checkgs: + /* On non-FSGSBASE systems, conditionally do SWAPGS */ + testl %ebx, %ebx + jnz restore_regs_and_return_to_kernel + + /* We are returning to a context with user GSBASE */ + swapgs + jmp restore_regs_and_return_to_kernel +SYM_CODE_END(paranoid_exit) + +/* + * Save all registers in pt_regs, and switch GS if needed. + */ +SYM_CODE_START_LOCAL(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 + UNTRAIN_RET + +.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 + 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 + + /* + * Issue an LFENCE to prevent GS speculation, regardless of whether it is a + * kernel or user gsbase. + */ +.Lerror_entry_done_lfence: + FENCE_SWAPGS_KERNEL_ENTRY + ANNOTATE_UNRET_END + RET + +.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 + UNTRAIN_RET + + /* + * 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 +SYM_CODE_END(error_entry) + +SYM_CODE_START_LOCAL(error_return) + UNWIND_HINT_REGS + DEBUG_ENTRY_ASSERT_IRQS_OFF + testb $3, CS(%rsp) + jz restore_regs_and_return_to_kernel + jmp swapgs_restore_regs_and_return_to_usermode +SYM_CODE_END(error_return) + +/* + * 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. + */ +SYM_CODE_START(asm_exc_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 + UNTRAIN_RET + + /* + * 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 exc_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 exc_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 exc_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 + + movq %rsp, %rdi + movq $-1, %rsi + call exc_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 + + /* + * The above invocation of paranoid_entry stored the GSBASE + * related information in R/EBX depending on the availability + * of FSGSBASE. + * + * If FSGSBASE is enabled, restore the saved GSBASE value + * unconditionally, otherwise take the conditional SWAPGS path. + */ + ALTERNATIVE "jmp nmi_no_fsgsbase", "", X86_FEATURE_FSGSBASE + + wrgsbase %rbx + jmp nmi_restore + +nmi_no_fsgsbase: + /* EBX == 0 -> invoke SWAPGS */ + testl %ebx, %ebx + jnz nmi_restore + +nmi_swapgs: + swapgs + +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 +SYM_CODE_END(asm_exc_nmi) + +#ifndef CONFIG_IA32_EMULATION +/* + * This handles SYSCALL from 32-bit code. There is no way to program + * MSRs to fully disable 32-bit SYSCALL. + */ +SYM_CODE_START(ignore_sysret) + UNWIND_HINT_EMPTY + mov $-ENOSYS, %eax + sysretl +SYM_CODE_END(ignore_sysret) +#endif + +.pushsection .text, "ax" +SYM_CODE_START(rewind_stack_and_make_dead) + 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 make_task_dead +SYM_CODE_END(rewind_stack_and_make_dead) +.popsection |