process_vm_access.c

/*
 * 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
 * @task: task to read/write from
 * @mm: mm for task
 * @process_pages: struct pages area that can store at least
 *  nr_pages_to_copy struct page pointers
 * @pa: address of page in task to start copying from/to
 * @start_offset: offset in page to start copying from/to
 * @len: number of bytes to copy
 * @lvec: iovec array specifying where to copy to/from
 * @lvec_cnt: number of elements in iovec array
 * @lvec_current: index in iovec array we are up to
 * @lvec_offset: offset in bytes from current iovec iov_base we are up to
 * @vm_write: 0 means copy from, 1 means copy to
 * @nr_pages_to_copy: number of pages to copy
 * @bytes_copied: returns number of bytes successfully copied
 * Returns 0 on success, error code otherwise
 */
static int process_vm_rw_pages(struct task_struct *task,
			       struct mm_struct *mm,
			       struct page **process_pages,
			       unsigned long pa,
			       unsigned long start_offset,
			       unsigned long len,
			       struct iov_iter *iter,
			       int vm_write,
			       unsigned int nr_pages_to_copy,
			       ssize_t *bytes_copied)
{
	int pages_pinned;
	void *target_kaddr;
	int pgs_copied = 0;
	int j;
	int ret;
	ssize_t bytes_to_copy;
	ssize_t rc = 0;
	const struct iovec *iov = iter->iov;

	*bytes_copied = 0;

	/* Get the pages we're interested in */
	down_read(&mm->mmap_sem);
	pages_pinned = get_user_pages(task, mm, pa,
				      nr_pages_to_copy,
				      vm_write, 0, process_pages, NULL);
	up_read(&mm->mmap_sem);

	if (pages_pinned != nr_pages_to_copy) {
		rc = -EFAULT;
		goto end;
	}

	/* Do the copy for each page */
	for (pgs_copied = 0;
	     (pgs_copied < nr_pages_to_copy) && iter->nr_segs;
	     pgs_copied++) {
		/* Make sure we have a non zero length iovec */
		while (iter->nr_segs && iov->iov_len == 0) {
			iov++;
			iter->nr_segs--;
		}
		if (!iter->nr_segs)
			break;

		/*
		 * Will copy smallest of:
		 * - bytes remaining in page
		 * - bytes remaining in destination iovec
		 */
		bytes_to_copy = min_t(ssize_t, PAGE_SIZE - start_offset,
				      len - *bytes_copied);
		bytes_to_copy = min_t(ssize_t, bytes_to_copy,
				      iov->iov_len
				      - iter->iov_offset);

		target_kaddr = kmap(process_pages[pgs_copied]) + start_offset;

		if (vm_write)
			ret = copy_from_user(target_kaddr,
					     iov->iov_base
					     + iter->iov_offset,
					     bytes_to_copy);
		else
			ret = copy_to_user(iov->iov_base
					   + iter->iov_offset,
					   target_kaddr, bytes_to_copy);
		kunmap(process_pages[pgs_copied]);
		if (ret) {
			*bytes_copied += bytes_to_copy - ret;
			pgs_copied++;
			rc = -EFAULT;
			goto end;
		}
		*bytes_copied += bytes_to_copy;
		iter->iov_offset += bytes_to_copy;
		if (iter->iov_offset == iov->iov_len) {
			/*
			 * Need to copy remaining part of page into the
			 * next iovec if there are any bytes left in page
			 */
			iter->nr_segs--;
			iov++;
			iter->iov_offset = 0;
			start_offset = (start_offset + bytes_to_copy)
				% PAGE_SIZE;
			if (start_offset)
				pgs_copied--;
		} else {
			start_offset = 0;
		}
	}

end:
	if (vm_write) {
		for (j = 0; j < pages_pinned; j++) {
			if (j < pgs_copied)
				set_page_dirty_lock(process_pages[j]);
			put_page(process_pages[j]);
		}
	} else {
		for (j = 0; j < pages_pinned; j++)
			put_page(process_pages[j]);
	}

	iter->iov = iov;
	return rc;
}

/* 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
 * @lvec: iovec array specifying where to copy to/from locally
 * @lvec_cnt: number of elements in iovec array
 * @lvec_current: index in iovec array we are up to
 * @lvec_offset: offset in bytes from current iovec iov_base we are up to
 * @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
 * @bytes_copied: returns number of bytes successfully copied
 * 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,
				    ssize_t *bytes_copied)
{
	unsigned long pa = addr & PAGE_MASK;
	unsigned long start_offset = addr - pa;
	unsigned long nr_pages;
	ssize_t bytes_copied_loop;
	ssize_t rc = 0;
	unsigned long nr_pages_copied = 0;
	unsigned long nr_pages_to_copy;
	unsigned long max_pages_per_loop = PVM_MAX_KMALLOC_PAGES
		/ sizeof(struct pages *);

	*bytes_copied = 0;

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

	while ((nr_pages_copied < nr_pages) && iter->nr_segs) {
		nr_pages_to_copy = min(nr_pages - nr_pages_copied,
				       max_pages_per_loop);

		rc = process_vm_rw_pages(task, mm, process_pages, pa,
					 start_offset, len, iter,
					 vm_write, nr_pages_to_copy,
					 &bytes_copied_loop);
		start_offset = 0;
		*bytes_copied += bytes_copied_loop;

		if (rc < 0) {
			return rc;
		} else {
			len -= bytes_copied_loop;
			nr_pages_copied += nr_pages_to_copy;
			pa += nr_pages_to_copy * PAGE_SIZE;
		}
	}

	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
 * @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_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;
	ssize_t bytes_copied_loop;
	ssize_t bytes_copied = 0;
	unsigned long nr_pages = 0;
	unsigned long nr_pages_iov;
	ssize_t iov_len;

	/*
	 * 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);
	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 && iter->nr_segs; i++) {
		rc = process_vm_rw_single_vec(
			(unsigned long)rvec[i].iov_base, rvec[i].iov_len,
			iter, process_pages, mm, task, vm_write,
			&bytes_copied_loop);
		bytes_copied += bytes_copied_loop;
		if (rc != 0) {
			/* 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 (bytes_copied)
				rc = bytes_copied;
			goto put_mm;
		}
	}

	rc = bytes_copied;
put_mm:
	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;

	if (flags != 0)
		return -EINVAL;

	/* Check iovecs */
	if (vm_write)
		rc = rw_copy_check_uvector(WRITE, lvec, liovcnt, UIO_FASTIOV,
					   iovstack_l, &iov_l);
	else
		rc = rw_copy_check_uvector(READ, lvec, liovcnt, UIO_FASTIOV,
					   iovstack_l, &iov_l);
	if (rc <= 0)
		goto free_iovecs;

	iov_iter_init(&iter, iov_l, liovcnt, rc, 0);

	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);
	if (iov_l != iovstack_l)
		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

asmlinkage 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;

	if (flags != 0)
		return -EINVAL;

	if (vm_write)
		rc = compat_rw_copy_check_uvector(WRITE, lvec, liovcnt,
						  UIO_FASTIOV, iovstack_l,
						  &iov_l);
	else
		rc = compat_rw_copy_check_uvector(READ, lvec, liovcnt,
						  UIO_FASTIOV, iovstack_l,
						  &iov_l);
	if (rc <= 0)
		goto free_iovecs;
	iov_iter_init(&iter, iov_l, liovcnt, rc, 0);
	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);
	if (iov_l != iovstack_l)
		kfree(iov_l);
	return rc;
}

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

asmlinkage ssize_t
compat_sys_process_vm_writev(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)
{
	return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
				    riovcnt, flags, 1);
}

#endif