1 // SPDX-License-Identifier: GPL-2.0 2 #include <linux/ptrace.h> 3 #include <linux/sched.h> 4 #include <linux/sched/task_stack.h> 5 #include <linux/export.h> 6 #include <asm/syscall.h> 7 8 static int collect_syscall(struct task_struct *target, struct syscall_info *info) 9 { 10 struct pt_regs *regs; 11 12 if (!try_get_task_stack(target)) { 13 /* Task has no stack, so the task isn't in a syscall. */ 14 memset(info, 0, sizeof(*info)); 15 info->data.nr = -1; 16 return 0; 17 } 18 19 regs = task_pt_regs(target); 20 if (unlikely(!regs)) { 21 put_task_stack(target); 22 return -EAGAIN; 23 } 24 25 info->sp = user_stack_pointer(regs); 26 info->data.instruction_pointer = instruction_pointer(regs); 27 28 info->data.nr = syscall_get_nr(target, regs); 29 if (info->data.nr != -1L) 30 syscall_get_arguments(target, regs, 31 (unsigned long *)&info->data.args[0]); 32 33 put_task_stack(target); 34 return 0; 35 } 36 37 /** 38 * task_current_syscall - Discover what a blocked task is doing. 39 * @target: thread to examine 40 * @info: structure with the following fields: 41 * .sp - filled with user stack pointer 42 * .data.nr - filled with system call number or -1 43 * .data.args - filled with @maxargs system call arguments 44 * .data.instruction_pointer - filled with user PC 45 * 46 * If @target is blocked in a system call, returns zero with @info.data.nr 47 * set to the the call's number and @info.data.args filled in with its 48 * arguments. Registers not used for system call arguments may not be available 49 * and it is not kosher to use &struct user_regset calls while the system 50 * call is still in progress. Note we may get this result if @target 51 * has finished its system call but not yet returned to user mode, such 52 * as when it's stopped for signal handling or syscall exit tracing. 53 * 54 * If @target is blocked in the kernel during a fault or exception, 55 * returns zero with *@info.data.nr set to -1 and does not fill in 56 * @info.data.args. If so, it's now safe to examine @target using 57 * &struct user_regset get() calls as long as we're sure @target won't return 58 * to user mode. 59 * 60 * Returns -%EAGAIN if @target does not remain blocked. 61 */ 62 int task_current_syscall(struct task_struct *target, struct syscall_info *info) 63 { 64 long state; 65 unsigned long ncsw; 66 67 if (target == current) 68 return collect_syscall(target, info); 69 70 state = target->state; 71 if (unlikely(!state)) 72 return -EAGAIN; 73 74 ncsw = wait_task_inactive(target, state); 75 if (unlikely(!ncsw) || 76 unlikely(collect_syscall(target, info)) || 77 unlikely(wait_task_inactive(target, state) != ncsw)) 78 return -EAGAIN; 79 80 return 0; 81 } 82