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
8static 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(tsk: target)) {
14 /* Task has no stack, so the task isn't in a syscall. */
15 memset(s: info, c: 0, n: 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(tsk: 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(task: target, regs);
30 if (info->data.nr != -1L)
31 syscall_get_arguments(task: 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(tsk: 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 */
69int task_current_syscall(struct task_struct *target, struct syscall_info *info)
70{
71 unsigned long ncsw;
72 unsigned int state;
73
74 if (target == current)
75 return collect_syscall(target, info);
76
77 state = READ_ONCE(target->__state);
78 if (unlikely(!state))
79 return -EAGAIN;
80
81 ncsw = wait_task_inactive(target, match_state: 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