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