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    /*
     * 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