LXR linux/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
   8static 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 */
  69int task_current_syscall(struct task_struct *target, struct syscall_info *info)
  70{
  71        long state;
  72        unsigned long ncsw;
  73
  74        if (target == current)
  75                return collect_syscall(target, info);
  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, info)) ||
  84            unlikely(wait_task_inactive(target, state) != ncsw))
  85                return -EAGAIN;
  86
  87        return 0;
  88}
  89