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, 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  */
  64 int 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 }