| // SPDX-License-Identifier: GPL-2.0-only |
| /* |
| * common.c - C code for kernel entry and exit |
| * Copyright (c) 2015 Andrew Lutomirski |
| * |
| * Based on asm and ptrace code by many authors. The code here originated |
| * in ptrace.c and signal.c. |
| */ |
| |
| #include <linux/kernel.h> |
| #include <linux/sched.h> |
| #include <linux/sched/task_stack.h> |
| #include <linux/entry-common.h> |
| #include <linux/mm.h> |
| #include <linux/smp.h> |
| #include <linux/errno.h> |
| #include <linux/ptrace.h> |
| #include <linux/export.h> |
| #include <linux/nospec.h> |
| #include <linux/syscalls.h> |
| #include <linux/uaccess.h> |
| |
| #ifdef CONFIG_XEN_PV |
| #include <xen/xen-ops.h> |
| #include <xen/events.h> |
| #endif |
| |
| #include <asm/apic.h> |
| #include <asm/desc.h> |
| #include <asm/traps.h> |
| #include <asm/vdso.h> |
| #include <asm/cpufeature.h> |
| #include <asm/fpu/api.h> |
| #include <asm/nospec-branch.h> |
| #include <asm/io_bitmap.h> |
| #include <asm/syscall.h> |
| #include <asm/irq_stack.h> |
| |
| #ifdef CONFIG_X86_64 |
| |
| static __always_inline bool do_syscall_x64(struct pt_regs *regs, int nr) |
| { |
| /* |
| * Convert negative numbers to very high and thus out of range |
| * numbers for comparisons. |
| */ |
| unsigned int unr = nr; |
| |
| if (likely(unr < NR_syscalls)) { |
| unr = array_index_nospec(unr, NR_syscalls); |
| regs->ax = x64_sys_call(regs, unr); |
| return true; |
| } |
| return false; |
| } |
| |
| static __always_inline bool do_syscall_x32(struct pt_regs *regs, int nr) |
| { |
| /* |
| * Adjust the starting offset of the table, and convert numbers |
| * < __X32_SYSCALL_BIT to very high and thus out of range |
| * numbers for comparisons. |
| */ |
| unsigned int xnr = nr - __X32_SYSCALL_BIT; |
| |
| if (IS_ENABLED(CONFIG_X86_X32_ABI) && likely(xnr < X32_NR_syscalls)) { |
| xnr = array_index_nospec(xnr, X32_NR_syscalls); |
| regs->ax = x32_sys_call(regs, xnr); |
| return true; |
| } |
| return false; |
| } |
| |
| __visible noinstr void do_syscall_64(struct pt_regs *regs, int nr) |
| { |
| add_random_kstack_offset(); |
| nr = syscall_enter_from_user_mode(regs, nr); |
| |
| instrumentation_begin(); |
| |
| if (!do_syscall_x64(regs, nr) && !do_syscall_x32(regs, nr) && nr != -1) { |
| /* Invalid system call, but still a system call. */ |
| regs->ax = __x64_sys_ni_syscall(regs); |
| } |
| |
| instrumentation_end(); |
| syscall_exit_to_user_mode(regs); |
| } |
| #endif |
| |
| #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION) |
| static __always_inline int syscall_32_enter(struct pt_regs *regs) |
| { |
| if (IS_ENABLED(CONFIG_IA32_EMULATION)) |
| current_thread_info()->status |= TS_COMPAT; |
| |
| return (int)regs->orig_ax; |
| } |
| |
| #ifdef CONFIG_IA32_EMULATION |
| bool __ia32_enabled __ro_after_init = true; |
| #endif |
| |
| /* |
| * Invoke a 32-bit syscall. Called with IRQs on in CONTEXT_KERNEL. |
| */ |
| static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs, int nr) |
| { |
| /* |
| * Convert negative numbers to very high and thus out of range |
| * numbers for comparisons. |
| */ |
| unsigned int unr = nr; |
| |
| if (likely(unr < IA32_NR_syscalls)) { |
| unr = array_index_nospec(unr, IA32_NR_syscalls); |
| regs->ax = ia32_sys_call(regs, unr); |
| } else if (nr != -1) { |
| regs->ax = __ia32_sys_ni_syscall(regs); |
| } |
| } |
| |
| #ifdef CONFIG_IA32_EMULATION |
| static __always_inline bool int80_is_external(void) |
| { |
| const unsigned int offs = (0x80 / 32) * 0x10; |
| const u32 bit = BIT(0x80 % 32); |
| |
| /* The local APIC on XENPV guests is fake */ |
| if (cpu_feature_enabled(X86_FEATURE_XENPV)) |
| return false; |
| |
| /* |
| * If vector 0x80 is set in the APIC ISR then this is an external |
| * interrupt. Either from broken hardware or injected by a VMM. |
| * |
| * Note: In guest mode this is only valid for secure guests where |
| * the secure module fully controls the vAPIC exposed to the guest. |
| */ |
| return apic_read(APIC_ISR + offs) & bit; |
| } |
| |
| /** |
| * do_int80_emulation - 32-bit legacy syscall C entry from asm |
| * |
| * This entry point can be used by 32-bit and 64-bit programs to perform |
| * 32-bit system calls. Instances of INT $0x80 can be found inline in |
| * various programs and libraries. It is also used by the vDSO's |
| * __kernel_vsyscall fallback for hardware that doesn't support a faster |
| * entry method. Restarted 32-bit system calls also fall back to INT |
| * $0x80 regardless of what instruction was originally used to do the |
| * system call. |
| * |
| * This is considered a slow path. It is not used by most libc |
| * implementations on modern hardware except during process startup. |
| * |
| * The arguments for the INT $0x80 based syscall are on stack in the |
| * pt_regs structure: |
| * eax: system call number |
| * ebx, ecx, edx, esi, edi, ebp: arg1 - arg 6 |
| */ |
| __visible noinstr void do_int80_emulation(struct pt_regs *regs) |
| { |
| int nr; |
| |
| /* Kernel does not use INT $0x80! */ |
| if (unlikely(!user_mode(regs))) { |
| irqentry_enter(regs); |
| instrumentation_begin(); |
| panic("Unexpected external interrupt 0x80\n"); |
| } |
| |
| /* |
| * Establish kernel context for instrumentation, including for |
| * int80_is_external() below which calls into the APIC driver. |
| * Identical for soft and external interrupts. |
| */ |
| enter_from_user_mode(regs); |
| |
| instrumentation_begin(); |
| add_random_kstack_offset(); |
| |
| /* Validate that this is a soft interrupt to the extent possible */ |
| if (unlikely(int80_is_external())) |
| panic("Unexpected external interrupt 0x80\n"); |
| |
| /* |
| * The low level idtentry code pushed -1 into regs::orig_ax |
| * and regs::ax contains the syscall number. |
| * |
| * User tracing code (ptrace or signal handlers) might assume |
| * that the regs::orig_ax contains a 32-bit number on invoking |
| * a 32-bit syscall. |
| * |
| * Establish the syscall convention by saving the 32bit truncated |
| * syscall number in regs::orig_ax and by invalidating regs::ax. |
| */ |
| regs->orig_ax = regs->ax & GENMASK(31, 0); |
| regs->ax = -ENOSYS; |
| |
| nr = syscall_32_enter(regs); |
| |
| local_irq_enable(); |
| nr = syscall_enter_from_user_mode_work(regs, nr); |
| do_syscall_32_irqs_on(regs, nr); |
| |
| instrumentation_end(); |
| syscall_exit_to_user_mode(regs); |
| } |
| #else /* CONFIG_IA32_EMULATION */ |
| |
| /* Handles int $0x80 on a 32bit kernel */ |
| __visible noinstr void do_int80_syscall_32(struct pt_regs *regs) |
| { |
| int nr = syscall_32_enter(regs); |
| |
| add_random_kstack_offset(); |
| /* |
| * Subtlety here: if ptrace pokes something larger than 2^31-1 into |
| * orig_ax, the int return value truncates it. This matches |
| * the semantics of syscall_get_nr(). |
| */ |
| nr = syscall_enter_from_user_mode(regs, nr); |
| instrumentation_begin(); |
| |
| do_syscall_32_irqs_on(regs, nr); |
| |
| instrumentation_end(); |
| syscall_exit_to_user_mode(regs); |
| } |
| #endif /* !CONFIG_IA32_EMULATION */ |
| |
| static noinstr bool __do_fast_syscall_32(struct pt_regs *regs) |
| { |
| int nr = syscall_32_enter(regs); |
| int res; |
| |
| add_random_kstack_offset(); |
| /* |
| * This cannot use syscall_enter_from_user_mode() as it has to |
| * fetch EBP before invoking any of the syscall entry work |
| * functions. |
| */ |
| syscall_enter_from_user_mode_prepare(regs); |
| |
| instrumentation_begin(); |
| /* Fetch EBP from where the vDSO stashed it. */ |
| if (IS_ENABLED(CONFIG_X86_64)) { |
| /* |
| * Micro-optimization: the pointer we're following is |
| * explicitly 32 bits, so it can't be out of range. |
| */ |
| res = __get_user(*(u32 *)®s->bp, |
| (u32 __user __force *)(unsigned long)(u32)regs->sp); |
| } else { |
| res = get_user(*(u32 *)®s->bp, |
| (u32 __user __force *)(unsigned long)(u32)regs->sp); |
| } |
| |
| if (res) { |
| /* User code screwed up. */ |
| regs->ax = -EFAULT; |
| |
| local_irq_disable(); |
| instrumentation_end(); |
| irqentry_exit_to_user_mode(regs); |
| return false; |
| } |
| |
| nr = syscall_enter_from_user_mode_work(regs, nr); |
| |
| /* Now this is just like a normal syscall. */ |
| do_syscall_32_irqs_on(regs, nr); |
| |
| instrumentation_end(); |
| syscall_exit_to_user_mode(regs); |
| return true; |
| } |
| |
| /* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */ |
| __visible noinstr long do_fast_syscall_32(struct pt_regs *regs) |
| { |
| /* |
| * Called using the internal vDSO SYSENTER/SYSCALL32 calling |
| * convention. Adjust regs so it looks like we entered using int80. |
| */ |
| unsigned long landing_pad = (unsigned long)current->mm->context.vdso + |
| vdso_image_32.sym_int80_landing_pad; |
| |
| /* |
| * SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward |
| * so that 'regs->ip -= 2' lands back on an int $0x80 instruction. |
| * Fix it up. |
| */ |
| regs->ip = landing_pad; |
| |
| /* Invoke the syscall. If it failed, keep it simple: use IRET. */ |
| if (!__do_fast_syscall_32(regs)) |
| return 0; |
| |
| #ifdef CONFIG_X86_64 |
| /* |
| * Opportunistic SYSRETL: if possible, try to return using SYSRETL. |
| * SYSRETL is available on all 64-bit CPUs, so we don't need to |
| * bother with SYSEXIT. |
| * |
| * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP, |
| * because the ECX fixup above will ensure that this is essentially |
| * never the case. |
| */ |
| return regs->cs == __USER32_CS && regs->ss == __USER_DS && |
| regs->ip == landing_pad && |
| (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF)) == 0; |
| #else |
| /* |
| * Opportunistic SYSEXIT: if possible, try to return using SYSEXIT. |
| * |
| * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP, |
| * because the ECX fixup above will ensure that this is essentially |
| * never the case. |
| * |
| * We don't allow syscalls at all from VM86 mode, but we still |
| * need to check VM, because we might be returning from sys_vm86. |
| */ |
| return static_cpu_has(X86_FEATURE_SEP) && |
| regs->cs == __USER_CS && regs->ss == __USER_DS && |
| regs->ip == landing_pad && |
| (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF | X86_EFLAGS_VM)) == 0; |
| #endif |
| } |
| |
| /* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */ |
| __visible noinstr long do_SYSENTER_32(struct pt_regs *regs) |
| { |
| /* SYSENTER loses RSP, but the vDSO saved it in RBP. */ |
| regs->sp = regs->bp; |
| |
| /* SYSENTER clobbers EFLAGS.IF. Assume it was set in usermode. */ |
| regs->flags |= X86_EFLAGS_IF; |
| |
| return do_fast_syscall_32(regs); |
| } |
| #endif |
| |
| SYSCALL_DEFINE0(ni_syscall) |
| { |
| return -ENOSYS; |
| } |
| |
| #ifdef CONFIG_XEN_PV |
| #ifndef CONFIG_PREEMPTION |
| /* |
| * Some hypercalls issued by the toolstack can take many 10s of |
| * seconds. Allow tasks running hypercalls via the privcmd driver to |
| * be voluntarily preempted even if full kernel preemption is |
| * disabled. |
| * |
| * Such preemptible hypercalls are bracketed by |
| * xen_preemptible_hcall_begin() and xen_preemptible_hcall_end() |
| * calls. |
| */ |
| DEFINE_PER_CPU(bool, xen_in_preemptible_hcall); |
| EXPORT_SYMBOL_GPL(xen_in_preemptible_hcall); |
| |
| /* |
| * In case of scheduling the flag must be cleared and restored after |
| * returning from schedule as the task might move to a different CPU. |
| */ |
| static __always_inline bool get_and_clear_inhcall(void) |
| { |
| bool inhcall = __this_cpu_read(xen_in_preemptible_hcall); |
| |
| __this_cpu_write(xen_in_preemptible_hcall, false); |
| return inhcall; |
| } |
| |
| static __always_inline void restore_inhcall(bool inhcall) |
| { |
| __this_cpu_write(xen_in_preemptible_hcall, inhcall); |
| } |
| #else |
| static __always_inline bool get_and_clear_inhcall(void) { return false; } |
| static __always_inline void restore_inhcall(bool inhcall) { } |
| #endif |
| |
| static void __xen_pv_evtchn_do_upcall(struct pt_regs *regs) |
| { |
| struct pt_regs *old_regs = set_irq_regs(regs); |
| |
| inc_irq_stat(irq_hv_callback_count); |
| |
| xen_evtchn_do_upcall(); |
| |
| set_irq_regs(old_regs); |
| } |
| |
| __visible noinstr void xen_pv_evtchn_do_upcall(struct pt_regs *regs) |
| { |
| irqentry_state_t state = irqentry_enter(regs); |
| bool inhcall; |
| |
| instrumentation_begin(); |
| run_sysvec_on_irqstack_cond(__xen_pv_evtchn_do_upcall, regs); |
| |
| inhcall = get_and_clear_inhcall(); |
| if (inhcall && !WARN_ON_ONCE(state.exit_rcu)) { |
| irqentry_exit_cond_resched(); |
| instrumentation_end(); |
| restore_inhcall(inhcall); |
| } else { |
| instrumentation_end(); |
| irqentry_exit(regs, state); |
| } |
| } |
| #endif /* CONFIG_XEN_PV */ |