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 }