| /* |
| * 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 <linux/kernel.h> |
| #include <linux/sched.h> |
| #include <linux/mm.h> |
| #include <linux/smp.h> |
| #include <linux/errno.h> |
| #include <linux/ptrace.h> |
| #include <linux/tracehook.h> |
| #include <linux/audit.h> |
| #include <linux/seccomp.h> |
| #include <linux/signal.h> |
| #include <linux/export.h> |
| #include <linux/context_tracking.h> |
| #include <linux/user-return-notifier.h> |
| #include <linux/nospec.h> |
| #include <linux/uprobes.h> |
| #include <linux/syscalls.h> |
| |
| #include <asm/desc.h> |
| #include <asm/traps.h> |
| #include <asm/vdso.h> |
| #include <asm/uaccess.h> |
| #include <asm/cpufeature.h> |
| |
| #define CREATE_TRACE_POINTS |
| #include <trace/events/syscalls.h> |
| |
| #ifdef CONFIG_CONTEXT_TRACKING |
| /* Called on entry from user mode with IRQs off. */ |
| __visible inline void enter_from_user_mode(void) |
| { |
| CT_WARN_ON(ct_state() != CONTEXT_USER); |
| user_exit_irqoff(); |
| } |
| #else |
| static inline void enter_from_user_mode(void) {} |
| #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); |
| } |
| } |
| |
| /* |
| * Returns the syscall nr to run (which should match regs->orig_ax) or -1 |
| * to skip the syscall. |
| */ |
| static long syscall_trace_enter(struct pt_regs *regs) |
| { |
| u32 arch = in_ia32_syscall() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64; |
| |
| struct thread_info *ti = current_thread_info(); |
| unsigned long ret = 0; |
| bool emulated = false; |
| u32 work; |
| |
| if (IS_ENABLED(CONFIG_DEBUG_ENTRY)) |
| BUG_ON(regs != task_pt_regs(current)); |
| |
| work = ACCESS_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY; |
| |
| if (unlikely(work & _TIF_SYSCALL_EMU)) |
| emulated = true; |
| |
| if ((emulated || (work & _TIF_SYSCALL_TRACE)) && |
| tracehook_report_syscall_entry(regs)) |
| return -1L; |
| |
| if (emulated) |
| return -1L; |
| |
| #ifdef CONFIG_SECCOMP |
| /* |
| * Do seccomp after ptrace, to catch any tracer changes. |
| */ |
| 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; |
| } |
| |
| ret = __secure_computing(&sd); |
| if (ret == -1) |
| return ret; |
| } |
| #endif |
| |
| 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; |
| } |
| |
| #define EXIT_TO_USERMODE_LOOP_FLAGS \ |
| (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | \ |
| _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY) |
| |
| static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags) |
| { |
| /* |
| * 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) { |
| /* 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(); |
| |
| cached_flags = READ_ONCE(current_thread_info()->flags); |
| |
| if (!(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS)) |
| break; |
| } |
| } |
| |
| /* Called with IRQs disabled. */ |
| __visible inline void prepare_exit_to_usermode(struct pt_regs *regs) |
| { |
| struct thread_info *ti = current_thread_info(); |
| u32 cached_flags; |
| |
| addr_limit_user_check(); |
| |
| if (IS_ENABLED(CONFIG_PROVE_LOCKING) && WARN_ON(!irqs_disabled())) |
| local_irq_disable(); |
| |
| lockdep_sys_exit(); |
| |
| cached_flags = READ_ONCE(ti->flags); |
| |
| if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS)) |
| exit_to_usermode_loop(regs, cached_flags); |
| |
| #ifdef CONFIG_COMPAT |
| /* |
| * Compat syscalls set TS_COMPAT. Make sure we clear it before |
| * returning to user mode. We need to clear it *after* signal |
| * handling, because syscall restart has a fixup for compat |
| * syscalls. The fixup is exercised by the ptrace_syscall_32 |
| * selftest. |
| * |
| * We also need to clear TS_REGS_POKED_I386: the 32-bit tracer |
| * special case only applies after poking regs and before the |
| * very next return to user mode. |
| */ |
| ti->status &= ~(TS_COMPAT|TS_I386_REGS_POKED); |
| #endif |
| |
| user_enter_irqoff(); |
| } |
| |
| #define SYSCALL_EXIT_WORK_FLAGS \ |
| (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \ |
| _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT) |
| |
| static void syscall_slow_exit_work(struct pt_regs *regs, u32 cached_flags) |
| { |
| bool step; |
| |
| 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); |
| } |
| |
| /* |
| * 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 inline void syscall_return_slowpath(struct pt_regs *regs) |
| { |
| struct thread_info *ti = current_thread_info(); |
| u32 cached_flags = READ_ONCE(ti->flags); |
| |
| CT_WARN_ON(ct_state() != CONTEXT_KERNEL); |
| |
| if (IS_ENABLED(CONFIG_PROVE_LOCKING) && |
| 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 (unlikely(cached_flags & SYSCALL_EXIT_WORK_FLAGS)) |
| syscall_slow_exit_work(regs, cached_flags); |
| |
| local_irq_disable(); |
| prepare_exit_to_usermode(regs); |
| } |
| |
| #ifdef CONFIG_X86_64 |
| __visible void do_syscall_64(struct pt_regs *regs) |
| { |
| struct thread_info *ti = current_thread_info(); |
| unsigned long nr = regs->orig_ax; |
| |
| enter_from_user_mode(); |
| local_irq_enable(); |
| |
| if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) |
| nr = syscall_trace_enter(regs); |
| |
| /* |
| * NB: Native and x32 syscalls are dispatched from the same |
| * table. The only functional difference is the x32 bit in |
| * regs->orig_ax, which changes the behavior of some syscalls. |
| */ |
| if (likely((nr & __SYSCALL_MASK) < NR_syscalls)) { |
| nr = array_index_nospec(nr & __SYSCALL_MASK, NR_syscalls); |
| regs->ax = sys_call_table[nr]( |
| regs->di, regs->si, regs->dx, |
| regs->r10, regs->r8, regs->r9); |
| } |
| |
| syscall_return_slowpath(regs); |
| } |
| #endif |
| |
| #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION) |
| /* |
| * Does a 32-bit syscall. Called with IRQs on in CONTEXT_KERNEL. Does |
| * all entry and exit work and returns with IRQs off. This function is |
| * extremely hot in workloads that use it, and it's usually called from |
| * do_fast_syscall_32, so forcibly inline it to improve performance. |
| */ |
| static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs) |
| { |
| struct thread_info *ti = current_thread_info(); |
| unsigned int nr = (unsigned int)regs->orig_ax; |
| |
| #ifdef CONFIG_IA32_EMULATION |
| ti->status |= TS_COMPAT; |
| #endif |
| |
| if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) { |
| /* |
| * Subtlety here: if ptrace pokes something larger than |
| * 2^32-1 into orig_ax, this truncates it. This may or |
| * may not be necessary, but it matches the old asm |
| * behavior. |
| */ |
| nr = syscall_trace_enter(regs); |
| } |
| |
| if (likely(nr < IA32_NR_syscalls)) { |
| nr = array_index_nospec(nr, IA32_NR_syscalls); |
| /* |
| * It's possible that a 32-bit syscall implementation |
| * takes a 64-bit parameter but nonetheless assumes that |
| * the high bits are zero. Make sure we zero-extend all |
| * of the args. |
| */ |
| regs->ax = ia32_sys_call_table[nr]( |
| (unsigned int)regs->bx, (unsigned int)regs->cx, |
| (unsigned int)regs->dx, (unsigned int)regs->si, |
| (unsigned int)regs->di, (unsigned int)regs->bp); |
| } |
| |
| syscall_return_slowpath(regs); |
| } |
| |
| /* Handles int $0x80 */ |
| __visible void do_int80_syscall_32(struct pt_regs *regs) |
| { |
| enter_from_user_mode(); |
| local_irq_enable(); |
| do_syscall_32_irqs_on(regs); |
| } |
| |
| /* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */ |
| __visible 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; |
| |
| enter_from_user_mode(); |
| |
| local_irq_enable(); |
| |
| /* Fetch EBP from where the vDSO stashed it. */ |
| if ( |
| #ifdef CONFIG_X86_64 |
| /* |
| * Micro-optimization: the pointer we're following is explicitly |
| * 32 bits, so it can't be out of range. |
| */ |
| __get_user(*(u32 *)®s->bp, |
| (u32 __user __force *)(unsigned long)(u32)regs->sp) |
| #else |
| get_user(*(u32 *)®s->bp, |
| (u32 __user __force *)(unsigned long)(u32)regs->sp) |
| #endif |
| ) { |
| |
| /* User code screwed up. */ |
| local_irq_disable(); |
| regs->ax = -EFAULT; |
| prepare_exit_to_usermode(regs); |
| return 0; /* Keep it simple: use IRET. */ |
| } |
| |
| /* Now this is just like a normal syscall. */ |
| do_syscall_32_irqs_on(regs); |
| |
| #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 |
| } |
| #endif |