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 unsigned long args[6] = { }; 11 struct pt_regs *regs; 12 13 if (!try_get_task_stack(target)) { 14 /* Task has no stack, so the task isn't in a syscall. */ 15 memset(info, 0, sizeof(*info)); 16 info->data.nr = -1; 17 return 0; 18 } 19 20 regs = task_pt_regs(target); 21 if (unlikely(!regs)) { 22 put_task_stack(target); 23 return -EAGAIN; 24 } 25 26 info->sp = user_stack_pointer(regs); 27 info->data.instruction_pointer = instruction_pointer(regs); 28 29 info->data.nr = syscall_get_nr(target, regs); 30 if (info->data.nr != -1L) 31 syscall_get_arguments(target, regs, args); 32 33 info->data.args[0] = args[0]; 34 info->data.args[1] = args[1]; 35 info->data.args[2] = args[2]; 36 info->data.args[3] = args[3]; 37 info->data.args[4] = args[4]; 38 info->data.args[5] = args[5]; 39 40 put_task_stack(target); 41 return 0; 42 } 43 44 /** 45 * task_current_syscall - Discover what a blocked task is doing. 46 * @target: thread to examine 47 * @info: structure with the following fields: 48 * .sp - filled with user stack pointer 49 * .data.nr - filled with system call number or -1 50 * .data.args - filled with @maxargs system call arguments 51 * .data.instruction_pointer - filled with user PC 52 * 53 * If @target is blocked in a system call, returns zero with @info.data.nr 54 * set to the call's number and @info.data.args filled in with its 55 * arguments. Registers not used for system call arguments may not be available 56 * and it is not kosher to use &struct user_regset calls while the system 57 * call is still in progress. Note we may get this result if @target 58 * has finished its system call but not yet returned to user mode, such 59 * as when it's stopped for signal handling or syscall exit tracing. 60 * 61 * If @target is blocked in the kernel during a fault or exception, 62 * returns zero with *@info.data.nr set to -1 and does not fill in 63 * @info.data.args. If so, it's now safe to examine @target using 64 * &struct user_regset get() calls as long as we're sure @target won't return 65 * to user mode. 66 * 67 * Returns -%EAGAIN if @target does not remain blocked. 68 */ 69 int task_current_syscall(struct task_struct *target, struct syscall_info *info) 70 { 71 long state; 72 unsigned long ncsw; 73 74 if (target == current) 75 return collect_syscall(target, info); 76 77 state = target->state; 78 if (unlikely(!state)) 79 return -EAGAIN; 80 81 ncsw = wait_task_inactive(target, state); 82 if (unlikely(!ncsw) || 83 unlikely(collect_syscall(target, info)) || 84 unlikely(wait_task_inactive(target, state) != ncsw)) 85 return -EAGAIN; 86 87 return 0; 88 } 89