/* * common.c - C code for kernel entry and exit * Copyright (c) 2015 Andrew Lutomirski * GPL v2 * * Based on asm and ptrace code by many authors. The code here originated * in ptrace.c and signal.c. */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #define CREATE_TRACE_POINTS #include #ifdef CONFIG_CONTEXT_TRACKING /* Called on entry from user mode with IRQs off. */ __visible void enter_from_user_mode(void) { CT_WARN_ON(ct_state() != CONTEXT_USER); user_exit(); } #endif static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch) { #ifdef CONFIG_X86_64 if (arch == AUDIT_ARCH_X86_64) { audit_syscall_entry(regs->orig_ax, regs->di, regs->si, regs->dx, regs->r10); } else #endif { audit_syscall_entry(regs->orig_ax, regs->bx, regs->cx, regs->dx, regs->si); } } /* * We can return 0 to resume the syscall or anything else to go to phase * 2. If we resume the syscall, we need to put something appropriate in * regs->orig_ax. * * NB: We don't have full pt_regs here, but regs->orig_ax and regs->ax * are fully functional. * * For phase 2's benefit, our return value is: * 0: resume the syscall * 1: go to phase 2; no seccomp phase 2 needed * anything else: go to phase 2; pass return value to seccomp */ unsigned long syscall_trace_enter_phase1(struct pt_regs *regs, u32 arch) { unsigned long ret = 0; u32 work; BUG_ON(regs != task_pt_regs(current)); work = ACCESS_ONCE(current_thread_info()->flags) & _TIF_WORK_SYSCALL_ENTRY; #ifdef CONFIG_CONTEXT_TRACKING /* * If TIF_NOHZ is set, we are required to call user_exit() before * doing anything that could touch RCU. */ if (work & _TIF_NOHZ) { enter_from_user_mode(); work &= ~_TIF_NOHZ; } #endif #ifdef CONFIG_SECCOMP /* * Do seccomp first -- it should minimize exposure of other * code, and keeping seccomp fast is probably more valuable * than the rest of this. */ if (work & _TIF_SECCOMP) { struct seccomp_data sd; sd.arch = arch; sd.nr = regs->orig_ax; sd.instruction_pointer = regs->ip; #ifdef CONFIG_X86_64 if (arch == AUDIT_ARCH_X86_64) { sd.args[0] = regs->di; sd.args[1] = regs->si; sd.args[2] = regs->dx; sd.args[3] = regs->r10; sd.args[4] = regs->r8; sd.args[5] = regs->r9; } else #endif { sd.args[0] = regs->bx; sd.args[1] = regs->cx; sd.args[2] = regs->dx; sd.args[3] = regs->si; sd.args[4] = regs->di; sd.args[5] = regs->bp; } BUILD_BUG_ON(SECCOMP_PHASE1_OK != 0); BUILD_BUG_ON(SECCOMP_PHASE1_SKIP != 1); ret = seccomp_phase1(&sd); if (ret == SECCOMP_PHASE1_SKIP) { regs->orig_ax = -1; ret = 0; } else if (ret != SECCOMP_PHASE1_OK) { return ret; /* Go directly to phase 2 */ } work &= ~_TIF_SECCOMP; } #endif /* Do our best to finish without phase 2. */ if (work == 0) return ret; /* seccomp and/or nohz only (ret == 0 here) */ #ifdef CONFIG_AUDITSYSCALL if (work == _TIF_SYSCALL_AUDIT) { /* * If there is no more work to be done except auditing, * then audit in phase 1. Phase 2 always audits, so, if * we audit here, then we can't go on to phase 2. */ do_audit_syscall_entry(regs, arch); return 0; } #endif return 1; /* Something is enabled that we can't handle in phase 1 */ } /* Returns the syscall nr to run (which should match regs->orig_ax). */ long syscall_trace_enter_phase2(struct pt_regs *regs, u32 arch, unsigned long phase1_result) { long ret = 0; u32 work = ACCESS_ONCE(current_thread_info()->flags) & _TIF_WORK_SYSCALL_ENTRY; BUG_ON(regs != task_pt_regs(current)); /* * If we stepped into a sysenter/syscall insn, it trapped in * kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP. * If user-mode had set TF itself, then it's still clear from * do_debug() and we need to set it again to restore the user * state. If we entered on the slow path, TF was already set. */ if (work & _TIF_SINGLESTEP) regs->flags |= X86_EFLAGS_TF; #ifdef CONFIG_SECCOMP /* * Call seccomp_phase2 before running the other hooks so that * they can see any changes made by a seccomp tracer. */ if (phase1_result > 1 && seccomp_phase2(phase1_result)) { /* seccomp failures shouldn't expose any additional code. */ return -1; } #endif if (unlikely(work & _TIF_SYSCALL_EMU)) ret = -1L; if ((ret || test_thread_flag(TIF_SYSCALL_TRACE)) && tracehook_report_syscall_entry(regs)) ret = -1L; if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT))) trace_sys_enter(regs, regs->orig_ax); do_audit_syscall_entry(regs, arch); return ret ?: regs->orig_ax; } long syscall_trace_enter(struct pt_regs *regs) { u32 arch = is_ia32_task() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64; unsigned long phase1_result = syscall_trace_enter_phase1(regs, arch); if (phase1_result == 0) return regs->orig_ax; else return syscall_trace_enter_phase2(regs, arch, phase1_result); } static struct thread_info *pt_regs_to_thread_info(struct pt_regs *regs) { unsigned long top_of_stack = (unsigned long)(regs + 1) + TOP_OF_KERNEL_STACK_PADDING; return (struct thread_info *)(top_of_stack - THREAD_SIZE); } /* Called with IRQs disabled. */ __visible void prepare_exit_to_usermode(struct pt_regs *regs) { if (WARN_ON(!irqs_disabled())) local_irq_disable(); /* * In order to return to user mode, we need to have IRQs off with * none of _TIF_SIGPENDING, _TIF_NOTIFY_RESUME, _TIF_USER_RETURN_NOTIFY, * _TIF_UPROBE, or _TIF_NEED_RESCHED set. Several of these flags * can be set at any time on preemptable kernels if we have IRQs on, * so we need to loop. Disabling preemption wouldn't help: doing the * work to clear some of the flags can sleep. */ while (true) { u32 cached_flags = READ_ONCE(pt_regs_to_thread_info(regs)->flags); if (!(cached_flags & (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY))) break; /* We have work to do. */ local_irq_enable(); if (cached_flags & _TIF_NEED_RESCHED) schedule(); if (cached_flags & _TIF_UPROBE) uprobe_notify_resume(regs); /* deal with pending signal delivery */ if (cached_flags & _TIF_SIGPENDING) do_signal(regs); if (cached_flags & _TIF_NOTIFY_RESUME) { clear_thread_flag(TIF_NOTIFY_RESUME); tracehook_notify_resume(regs); } if (cached_flags & _TIF_USER_RETURN_NOTIFY) fire_user_return_notifiers(); /* Disable IRQs and retry */ local_irq_disable(); } user_enter(); } /* * Called with IRQs on and fully valid regs. Returns with IRQs off in a * state such that we can immediately switch to user mode. */ __visible void syscall_return_slowpath(struct pt_regs *regs) { struct thread_info *ti = pt_regs_to_thread_info(regs); u32 cached_flags = READ_ONCE(ti->flags); bool step; CT_WARN_ON(ct_state() != CONTEXT_KERNEL); if (WARN(irqs_disabled(), "syscall %ld left IRQs disabled", regs->orig_ax)) local_irq_enable(); /* * First do one-time work. If these work items are enabled, we * want to run them exactly once per syscall exit with IRQs on. */ if (cached_flags & (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT)) { audit_syscall_exit(regs); if (cached_flags & _TIF_SYSCALL_TRACEPOINT) trace_sys_exit(regs, regs->ax); /* * If TIF_SYSCALL_EMU is set, we only get here because of * TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP). * We already reported this syscall instruction in * syscall_trace_enter(). */ step = unlikely( (cached_flags & (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU)) == _TIF_SINGLESTEP); if (step || cached_flags & _TIF_SYSCALL_TRACE) tracehook_report_syscall_exit(regs, step); } #ifdef CONFIG_COMPAT /* * Compat syscalls set TS_COMPAT. Make sure we clear it before * returning to user mode. */ ti->status &= ~TS_COMPAT; #endif local_irq_disable(); prepare_exit_to_usermode(regs); }