lib/syscall.c

   1 #include <linux/ptrace.h>
   2 #include <linux/sched.h>
   3 #include <linux/sched/task_stack.h>
   4 #include <linux/export.h>
   5 #include <asm/syscall.h>
   6
   7 static int collect_syscall(struct task_struct *target, long *callno,
   8                            unsigned long args[6], unsigned int maxargs,
   9                            unsigned long *sp, unsigned long *pc)
  10 {
  11         struct pt_regs *regs;
  12
  13         if (!try_get_task_stack(target)) {
  14                 /* Task has no stack, so the task isn't in a syscall. */
  15                 *sp = *pc = 0;
  16                 *callno = -1;
  17                 return 0;
  18         }
  19
  20         regs = task_pt_regs(target);
  21         if (unlikely(!regs)) {
  22                 put_task_stack(target);
  23                 return -EAGAIN;
  24         }
  25
  26         *sp = user_stack_pointer(regs);
  27         *pc = instruction_pointer(regs);
  28
  29         *callno = syscall_get_nr(target, regs);
  30         if (*callno != -1L && maxargs > 0)
  31                 syscall_get_arguments(target, regs, 0, maxargs, args);
  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  * @callno:             filled with system call number or -1
  41  * @args:               filled with @maxargs system call arguments
  42  * @maxargs:            number of elements in @args to fill
  43  * @sp:                 filled with user stack pointer
  44  * @pc:                 filled with user PC
  45  *
  46  * If @target is blocked in a system call, returns zero with *@callno
  47  * set to the the call's number and @args filled in with its arguments.
  48  * Registers not used for system call arguments may not be available and
  49  * 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 *@callno set to -1 and does not fill in @args.
  56  * If so, it's now safe to examine @target using &struct user_regset
  57  * get() calls as long as we're sure @target won't return to user mode.
  58  *
  59  * Returns -%EAGAIN if @target does not remain blocked.
  60  *
  61  * Returns -%EINVAL if @maxargs is too large (maximum is six).
  62  */
  63 int task_current_syscall(struct task_struct *target, long *callno,
  64                          unsigned long args[6], unsigned int maxargs,
  65                          unsigned long *sp, unsigned long *pc)
  66 {
  67         long state;
  68         unsigned long ncsw;
  69
  70         if (unlikely(maxargs > 6))
  71                 return -EINVAL;
  72
  73         if (target == current)
  74                 return collect_syscall(target, callno, args, maxargs, sp, pc);
  75
  76         state = target->state;
  77         if (unlikely(!state))
  78                 return -EAGAIN;
  79
  80         ncsw = wait_task_inactive(target, state);
  81         if (unlikely(!ncsw) ||
  82             unlikely(collect_syscall(target, callno, args, maxargs, sp, pc)) ||
  83             unlikely(wait_task_inactive(target, state) != ncsw))
  84                 return -EAGAIN;
  85
  86         return 0;
  87 }