| /* 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" |
| |
| /* |
| * 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 |
| ENDBR |
| |
| 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(pcpu_hot + X86_top_of_stack), %rsp |
| |
| SYM_INNER_LABEL(entry_SYSCALL_64_safe_stack, SYM_L_GLOBAL) |
| ANNOTATE_NOENDBR |
| |
| /* 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 %rsp, %rdi |
| /* Sign extend the lower 32bit as syscall numbers are treated as int */ |
| movslq %eax, %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. |
| * In the Xen PV case we must use iret anyway. |
| */ |
| |
| ALTERNATIVE "", "jmp swapgs_restore_regs_and_return_to_usermode", \ |
| X86_FEATURE_XENPV |
| |
| 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 |
| SYM_INNER_LABEL(entry_SYSRETQ_unsafe_stack, SYM_L_GLOBAL) |
| ANNOTATE_NOENDBR |
| swapgs |
| sysretq |
| SYM_INNER_LABEL(entry_SYSRETQ_end, SYM_L_GLOBAL) |
| ANNOTATE_NOENDBR |
| int3 |
| 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) + FIXED_stack_canary |
| #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" |
| __FUNC_ALIGN |
| SYM_CODE_START_NOALIGN(ret_from_fork) |
| UNWIND_HINT_EMPTY |
| ANNOTATE_NOENDBR // copy_thread |
| CALL_DEPTH_ACCOUNT |
| 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 |
| testl $X86_EFLAGS_IF, %eax |
| jz .Lokay_\@ |
| ud2 |
| .Lokay_\@: |
| popq %rax |
| #endif |
| .endm |
| |
| SYM_CODE_START(xen_error_entry) |
| ANNOTATE_NOENDBR |
| UNWIND_HINT_FUNC |
| PUSH_AND_CLEAR_REGS save_ret=1 |
| ENCODE_FRAME_POINTER 8 |
| UNTRAIN_RET_FROM_CALL |
| RET |
| SYM_CODE_END(xen_error_entry) |
| |
| /** |
| * 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() and switch to the task stack if from userspace. |
| * |
| * When in XENPV, it is already in the task stack, and it can't fault |
| * for native_iret() nor native_load_gs_index() since XENPV uses its |
| * own pvops for IRET and load_gs_index(). And it doesn't need to |
| * switch the CR3. So it can skip invoking error_entry(). |
| */ |
| ALTERNATIVE "call error_entry; movq %rax, %rsp", \ |
| "call xen_error_entry", X86_FEATURE_XENPV |
| |
| ENCODE_FRAME_POINTER |
| 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 |
| |
| /* For some configurations \cfunc ends up being a noreturn. */ |
| REACHABLE |
| |
| 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) |
| |
| .if \vector == X86_TRAP_BP |
| /* #BP advances %rip to the next instruction */ |
| UNWIND_HINT_IRET_REGS offset=\has_error_code*8 signal=0 |
| .else |
| UNWIND_HINT_IRET_REGS offset=\has_error_code*8 |
| .endif |
| |
| ENDBR |
| ASM_CLAC |
| cld |
| |
| .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 |
| ENDBR |
| ASM_CLAC |
| cld |
| |
| 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 |
| ENDBR |
| ASM_CLAC |
| cld |
| |
| /* |
| * 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 definitely 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 |
| ENDBR |
| ASM_CLAC |
| cld |
| |
| /* 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 |
| |
| /* For some configurations \cfunc ends up being a noreturn. */ |
| REACHABLE |
| |
| 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 |
| .globl __irqentry_text_start |
| __irqentry_text_start: |
| |
| #include <asm/idtentry.h> |
| |
| __ALIGN |
| .globl __irqentry_text_end |
| __irqentry_text_end: |
| ANNOTATE_NOENDBR |
| |
| 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 |
| jmp .Lnative_iret |
| |
| |
| 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. |
| */ |
| #ifdef CONFIG_XEN_PV |
| SYM_INNER_LABEL(early_xen_iret_patch, SYM_L_GLOBAL) |
| ANNOTATE_NOENDBR |
| .byte 0xe9 |
| .long .Lnative_iret - (. + 4) |
| #endif |
| |
| .Lnative_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 |
| |
| SYM_INNER_LABEL(native_irq_return_iret, SYM_L_GLOBAL) |
| ANNOTATE_NOENDBR // exc_double_fault |
| /* |
| * 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 */ |
| |
| 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 |
| * di: new selector |
| * |
| * Is in entry.text as it shouldn't be instrumented. |
| */ |
| SYM_FUNC_START(asm_load_gs_index) |
| FRAME_BEGIN |
| swapgs |
| .Lgs_change: |
| ANNOTATE_NOENDBR // error_entry |
| movl %edi, %gs |
| 2: ALTERNATIVE "", "mfence", X86_BUG_SWAPGS_FENCE |
| swapgs |
| FRAME_END |
| RET |
| |
| /* running with kernelgs */ |
| .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 |
| |
| _ASM_EXTABLE(.Lgs_change, .Lbad_gs) |
| |
| SYM_FUNC_END(asm_load_gs_index) |
| EXPORT_SYMBOL(asm_load_gs_index) |
| |
| #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) |
| */ |
| __FUNC_ALIGN |
| SYM_CODE_START_LOCAL_NOALIGN(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. |
| */ |
| __FUNC_ALIGN |
| SYM_CODE_START_NOALIGN(xen_failsafe_callback) |
| UNWIND_HINT_EMPTY |
| ENDBR |
| 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(paranoid_entry) |
| ANNOTATE_NOENDBR |
| UNWIND_HINT_FUNC |
| 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_FROM_CALL |
| |
| 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) |
| |
| /* |
| * Switch GS and CR3 if needed. |
| */ |
| SYM_CODE_START(error_entry) |
| ANNOTATE_NOENDBR |
| UNWIND_HINT_FUNC |
| |
| 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_FROM_CALL |
| |
| leaq 8(%rsp), %rdi /* arg0 = pt_regs pointer */ |
| /* Put us onto the real thread stack. */ |
| jmp sync_regs |
| |
| /* |
| * 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 |
| CALL_DEPTH_ACCOUNT |
| leaq 8(%rsp), %rax /* return pt_regs pointer */ |
| 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_FROM_CALL |
| |
| /* |
| * Pretend that the exception came from user mode: set up pt_regs |
| * as if we faulted immediately after IRET. |
| */ |
| leaq 8(%rsp), %rdi /* arg0 = pt_regs pointer */ |
| call fixup_bad_iret |
| mov %rax, %rdi |
| jmp sync_regs |
| 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 |
| ENDBR |
| |
| /* |
| * 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 |
| cld |
| |
| /* 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 |
| FENCE_SWAPGS_USER_ENTRY |
| SWITCH_TO_KERNEL_CR3 scratch_reg=%rdx |
| movq %rsp, %rdx |
| movq PER_CPU_VAR(pcpu_hot + X86_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: |
| ANNOTATE_NOENDBR // this code |
| /* |
| * 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: |
| ANNOTATE_NOENDBR // this code |
| |
| /* |
| * 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 |
| ENDBR |
| mov $-ENOSYS, %eax |
| sysretl |
| SYM_CODE_END(ignore_sysret) |
| #endif |
| |
| .pushsection .text, "ax" |
| __FUNC_ALIGN |
| SYM_CODE_START_NOALIGN(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(pcpu_hot + X86_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 |
