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(tsk: 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(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 | */ |
69 | int 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 | |