lib/syscall.c

   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 }