/*
   * linux/mm/process_vm_access.c
   *
   * Copyright (C) 2010-2011 Christopher Yeoh <cyeoh@au1.ibm.com>, IBM Corp.
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License
   * as published by the Free Software Foundation; either version
   * 2 of the License, or (at your option) any later version.
   */
  
  #include <linux/mm.h>
  #include <linux/uio.h>
  #include <linux/sched.h>
  #include <linux/highmem.h>
  #include <linux/ptrace.h>
  #include <linux/slab.h>
  #include <linux/syscalls.h>
  
  #ifdef CONFIG_COMPAT
  #include <linux/compat.h>
  #endif
  
  /**
   * process_vm_rw_pages - read/write pages from task specified

   * @pages: array of pointers to pages we want to copy

   * @start_offset: offset in page to start copying from/to
   * @len: number of bytes to copy

   * @iter: where to copy to/from locally

   * @vm_write: 0 means copy from, 1 means copy to

   * Returns 0 on success, error code otherwise
   */

  static int process_vm_rw_pages(struct page **pages,
  			       unsigned offset,

  			       size_t len,

  			       struct iov_iter *iter,

  			       int vm_write)

  {

  	/* Do the copy for each page */

  	while (len && iov_iter_count(iter)) {

  		struct page *page = *pages++;

  		size_t copy = PAGE_SIZE - offset;

  		size_t copied;

  		if (copy > len)
  			copy = len;

  		if (vm_write) {

  			copied = copy_page_from_iter(page, offset, copy, iter);

  			set_page_dirty_lock(page);

  		} else {

  			copied = copy_page_to_iter(page, offset, copy, iter);

  		}

  		len -= copied;
  		if (copied < copy && iov_iter_count(iter))
  			return -EFAULT;
  		offset = 0;

  	}

  	return 0;

  }
  
  /* Maximum number of pages kmalloc'd to hold struct page's during copy */
  #define PVM_MAX_KMALLOC_PAGES (PAGE_SIZE * 2)
  
  /**
   * process_vm_rw_single_vec - read/write pages from task specified
   * @addr: start memory address of target process
   * @len: size of area to copy to/from

   * @iter: where to copy to/from locally

   * @process_pages: struct pages area that can store at least
   *  nr_pages_to_copy struct page pointers
   * @mm: mm for task
   * @task: task to read/write from
   * @vm_write: 0 means copy from, 1 means copy to

   * Returns 0 on success or on failure error code
   */
  static int process_vm_rw_single_vec(unsigned long addr,
  				    unsigned long len,

  				    struct iov_iter *iter,

  				    struct page **process_pages,
  				    struct mm_struct *mm,
  				    struct task_struct *task,

  				    int vm_write)

  {
  	unsigned long pa = addr & PAGE_MASK;
  	unsigned long start_offset = addr - pa;
  	unsigned long nr_pages;

  	ssize_t rc = 0;

  	unsigned long max_pages_per_loop = PVM_MAX_KMALLOC_PAGES
  		/ sizeof(struct pages *);

  	unsigned int flags = FOLL_REMOTE;

  	/* Work out address and page range required */
  	if (len == 0)
  		return 0;
  	nr_pages = (addr + len - 1) / PAGE_SIZE - addr / PAGE_SIZE + 1;

  	if (vm_write)
  		flags |= FOLL_WRITE;

  	while (!rc && nr_pages && iov_iter_count(iter)) {
  		int pages = min(nr_pages, max_pages_per_loop);
  		size_t bytes;

  		/*
  		 * Get the pages we're interested in.  We must
  		 * add FOLL_REMOTE because task/mm might not
  		 * current/current->mm
  		 */
  		pages = __get_user_pages_unlocked(task, mm, pa, pages,

  						  process_pages, flags);

  		if (pages <= 0)

  			return -EFAULT;

  		bytes = pages * PAGE_SIZE - start_offset;
  		if (bytes > len)
  			bytes = len;

  		rc = process_vm_rw_pages(process_pages,

  					 start_offset, bytes, iter,

  					 vm_write);

  		len -= bytes;

  		start_offset = 0;

  		nr_pages -= pages;
  		pa += pages * PAGE_SIZE;
  		while (pages)
  			put_page(process_pages[--pages]);

  	}
  
  	return rc;
  }
  
  /* Maximum number of entries for process pages array
     which lives on stack */
  #define PVM_MAX_PP_ARRAY_COUNT 16
  
  /**
   * process_vm_rw_core - core of reading/writing pages from task specified
   * @pid: PID of process to read/write from/to

   * @iter: where to copy to/from locally

   * @rvec: iovec array specifying where to copy to/from in the other process
   * @riovcnt: size of rvec array
   * @flags: currently unused
   * @vm_write: 0 if reading from other process, 1 if writing to other process
   * Returns the number of bytes read/written or error code. May
   *  return less bytes than expected if an error occurs during the copying
   *  process.
   */

  static ssize_t process_vm_rw_core(pid_t pid, struct iov_iter *iter,

  				  const struct iovec *rvec,
  				  unsigned long riovcnt,
  				  unsigned long flags, int vm_write)
  {
  	struct task_struct *task;
  	struct page *pp_stack[PVM_MAX_PP_ARRAY_COUNT];
  	struct page **process_pages = pp_stack;
  	struct mm_struct *mm;
  	unsigned long i;
  	ssize_t rc = 0;

  	unsigned long nr_pages = 0;
  	unsigned long nr_pages_iov;

  	ssize_t iov_len;

  	size_t total_len = iov_iter_count(iter);

  
  	/*
  	 * Work out how many pages of struct pages we're going to need
  	 * when eventually calling get_user_pages
  	 */
  	for (i = 0; i < riovcnt; i++) {
  		iov_len = rvec[i].iov_len;
  		if (iov_len > 0) {
  			nr_pages_iov = ((unsigned long)rvec[i].iov_base
  					+ iov_len)
  				/ PAGE_SIZE - (unsigned long)rvec[i].iov_base
  				/ PAGE_SIZE + 1;
  			nr_pages = max(nr_pages, nr_pages_iov);
  		}
  	}
  
  	if (nr_pages == 0)
  		return 0;
  
  	if (nr_pages > PVM_MAX_PP_ARRAY_COUNT) {
  		/* For reliability don't try to kmalloc more than
  		   2 pages worth */
  		process_pages = kmalloc(min_t(size_t, PVM_MAX_KMALLOC_PAGES,
  					      sizeof(struct pages *)*nr_pages),
  					GFP_KERNEL);
  
  		if (!process_pages)
  			return -ENOMEM;
  	}
  
  	/* Get process information */
  	rcu_read_lock();
  	task = find_task_by_vpid(pid);
  	if (task)
  		get_task_struct(task);
  	rcu_read_unlock();
  	if (!task) {
  		rc = -ESRCH;
  		goto free_proc_pages;
  	}

  	mm = mm_access(task, PTRACE_MODE_ATTACH_REALCREDS);

  	if (!mm || IS_ERR(mm)) {
  		rc = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
  		/*
  		 * Explicitly map EACCES to EPERM as EPERM is a more a
  		 * appropriate error code for process_vw_readv/writev
  		 */
  		if (rc == -EACCES)
  			rc = -EPERM;

  		goto put_task_struct;
  	}

  	for (i = 0; i < riovcnt && iov_iter_count(iter) && !rc; i++)

  		rc = process_vm_rw_single_vec(
  			(unsigned long)rvec[i].iov_base, rvec[i].iov_len,

  			iter, process_pages, mm, task, vm_write);
  
  	/* copied = space before - space after */
  	total_len -= iov_iter_count(iter);
  
  	/* If we have managed to copy any data at all then
  	   we return the number of bytes copied. Otherwise
  	   we return the error code */
  	if (total_len)
  		rc = total_len;

  	mmput(mm);
  
  put_task_struct:
  	put_task_struct(task);
  
  free_proc_pages:
  	if (process_pages != pp_stack)
  		kfree(process_pages);
  	return rc;
  }
  
  /**
   * process_vm_rw - check iovecs before calling core routine
   * @pid: PID of process to read/write from/to
   * @lvec: iovec array specifying where to copy to/from locally
   * @liovcnt: size of lvec array
   * @rvec: iovec array specifying where to copy to/from in the other process
   * @riovcnt: size of rvec array
   * @flags: currently unused
   * @vm_write: 0 if reading from other process, 1 if writing to other process
   * Returns the number of bytes read/written or error code. May
   *  return less bytes than expected if an error occurs during the copying
   *  process.
   */
  static ssize_t process_vm_rw(pid_t pid,
  			     const struct iovec __user *lvec,
  			     unsigned long liovcnt,
  			     const struct iovec __user *rvec,
  			     unsigned long riovcnt,
  			     unsigned long flags, int vm_write)
  {
  	struct iovec iovstack_l[UIO_FASTIOV];
  	struct iovec iovstack_r[UIO_FASTIOV];
  	struct iovec *iov_l = iovstack_l;
  	struct iovec *iov_r = iovstack_r;

  	struct iov_iter iter;

  	ssize_t rc;

  	int dir = vm_write ? WRITE : READ;

  
  	if (flags != 0)
  		return -EINVAL;
  
  	/* Check iovecs */

  	rc = import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
  	if (rc < 0)
  		return rc;
  	if (!iov_iter_count(&iter))

  		goto free_iovecs;

  	rc = rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt, UIO_FASTIOV,
  				   iovstack_r, &iov_r);

  	if (rc <= 0)
  		goto free_iovecs;

  	rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);

  
  free_iovecs:
  	if (iov_r != iovstack_r)
  		kfree(iov_r);

  	kfree(iov_l);

  
  	return rc;
  }
  
  SYSCALL_DEFINE6(process_vm_readv, pid_t, pid, const struct iovec __user *, lvec,
  		unsigned long, liovcnt, const struct iovec __user *, rvec,
  		unsigned long, riovcnt,	unsigned long, flags)
  {
  	return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 0);
  }
  
  SYSCALL_DEFINE6(process_vm_writev, pid_t, pid,
  		const struct iovec __user *, lvec,
  		unsigned long, liovcnt, const struct iovec __user *, rvec,
  		unsigned long, riovcnt,	unsigned long, flags)
  {
  	return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 1);
  }
  
  #ifdef CONFIG_COMPAT

  static ssize_t

  compat_process_vm_rw(compat_pid_t pid,
  		     const struct compat_iovec __user *lvec,
  		     unsigned long liovcnt,
  		     const struct compat_iovec __user *rvec,
  		     unsigned long riovcnt,
  		     unsigned long flags, int vm_write)
  {
  	struct iovec iovstack_l[UIO_FASTIOV];
  	struct iovec iovstack_r[UIO_FASTIOV];
  	struct iovec *iov_l = iovstack_l;
  	struct iovec *iov_r = iovstack_r;

  	struct iov_iter iter;

  	ssize_t rc = -EFAULT;

  	int dir = vm_write ? WRITE : READ;

  
  	if (flags != 0)
  		return -EINVAL;

  	rc = compat_import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
  	if (rc < 0)
  		return rc;
  	if (!iov_iter_count(&iter))

  		goto free_iovecs;

  	rc = compat_rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt,

  					  UIO_FASTIOV, iovstack_r,

  					  &iov_r);

  	if (rc <= 0)
  		goto free_iovecs;

  	rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);

  
  free_iovecs:
  	if (iov_r != iovstack_r)
  		kfree(iov_r);

  	kfree(iov_l);

  	return rc;
  }

  COMPAT_SYSCALL_DEFINE6(process_vm_readv, compat_pid_t, pid,
  		       const struct compat_iovec __user *, lvec,
  		       compat_ulong_t, liovcnt,
  		       const struct compat_iovec __user *, rvec,
  		       compat_ulong_t, riovcnt,
  		       compat_ulong_t, flags)

  {
  	return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
  				    riovcnt, flags, 0);
  }

  COMPAT_SYSCALL_DEFINE6(process_vm_writev, compat_pid_t, pid,
  		       const struct compat_iovec __user *, lvec,
  		       compat_ulong_t, liovcnt,
  		       const struct compat_iovec __user *, rvec,
  		       compat_ulong_t, riovcnt,
  		       compat_ulong_t, flags)

  {
  	return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
  				    riovcnt, flags, 1);
  }
  
  #endif