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         unsigned long args[6] = { };
  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                 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(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(target, regs);
  30         if (info->data.nr != -1L)
  31                 syscall_get_arguments(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(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, 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 }