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, 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 */
  64int 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}
  89