fs/f2fs/crypto.c - kernel/bruno - Git at Google

 /*
  * linux/fs/f2fs/crypto.c
  *
  * Copied from linux/fs/ext4/crypto.c
  *
  * Copyright (C) 2015, Google, Inc.
  * Copyright (C) 2015, Motorola Mobility
  *
  * This contains encryption functions for f2fs
  *
  * Written by Michael Halcrow, 2014.
  *
  * Filename encryption additions
  *	Uday Savagaonkar, 2014
  * Encryption policy handling additions
  *	Ildar Muslukhov, 2014
  * Remove ext4_encrypted_zeroout(),
  *   add f2fs_restore_and_release_control_page()
  *	Jaegeuk Kim, 2015.
  *
  * This has not yet undergone a rigorous security audit.
  *
  * The usage of AES-XTS should conform to recommendations in NIST
  * Special Publication 800-38E and IEEE P1619/D16.
  */
 #include <crypto/hash.h>
 #include <crypto/sha.h>
 #include <keys/user-type.h>
 #include <keys/encrypted-type.h>
 #include <linux/crypto.h>
 #include <linux/ecryptfs.h>
 #include <linux/gfp.h>
 #include <linux/kernel.h>
 #include <linux/key.h>
 #include <linux/list.h>
 #include <linux/mempool.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
 #include <linux/random.h>
 #include <linux/scatterlist.h>
 #include <linux/spinlock_types.h>
 #include <linux/f2fs_fs.h>
 #include <linux/ratelimit.h>
 #include <linux/bio.h>

 #include "f2fs.h"
 #include "xattr.h"

 /* Encryption added and removed here! (L: */

 static unsigned int num_prealloc_crypto_pages = 32;
 static unsigned int num_prealloc_crypto_ctxs = 128;

 module_param(num_prealloc_crypto_pages, uint, 0444);
 MODULE_PARM_DESC(num_prealloc_crypto_pages,
 		"Number of crypto pages to preallocate");
 module_param(num_prealloc_crypto_ctxs, uint, 0444);
 MODULE_PARM_DESC(num_prealloc_crypto_ctxs,
 		"Number of crypto contexts to preallocate");

 static mempool_t *f2fs_bounce_page_pool;

 static LIST_HEAD(f2fs_free_crypto_ctxs);
 static DEFINE_SPINLOCK(f2fs_crypto_ctx_lock);

 static struct workqueue_struct *f2fs_read_workqueue;
 static DEFINE_MUTEX(crypto_init);

 static struct kmem_cache *f2fs_crypto_ctx_cachep;
 struct kmem_cache *f2fs_crypt_info_cachep;

 /**
  * f2fs_release_crypto_ctx() - Releases an encryption context
  * @ctx: The encryption context to release.
  *
  * If the encryption context was allocated from the pre-allocated pool, returns
  * it to that pool. Else, frees it.
  *
  * If there's a bounce page in the context, this frees that.
  */
 void f2fs_release_crypto_ctx(struct f2fs_crypto_ctx *ctx)
 {
 	unsigned long flags;

 	if (ctx->flags & F2FS_WRITE_PATH_FL && ctx->w.bounce_page) {
 		mempool_free(ctx->w.bounce_page, f2fs_bounce_page_pool);
 		ctx->w.bounce_page = NULL;
 	}
 	ctx->w.control_page = NULL;
 	if (ctx->flags & F2FS_CTX_REQUIRES_FREE_ENCRYPT_FL) {
 		kmem_cache_free(f2fs_crypto_ctx_cachep, ctx);
 	} else {
 		spin_lock_irqsave(&f2fs_crypto_ctx_lock, flags);
 		list_add(&ctx->free_list, &f2fs_free_crypto_ctxs);
 		spin_unlock_irqrestore(&f2fs_crypto_ctx_lock, flags);
 	}
 }

 /**
  * f2fs_get_crypto_ctx() - Gets an encryption context
  * @inode:       The inode for which we are doing the crypto
  *
  * Allocates and initializes an encryption context.
  *
  * Return: An allocated and initialized encryption context on success; error
  * value or NULL otherwise.
  */
 struct f2fs_crypto_ctx *f2fs_get_crypto_ctx(struct inode *inode)
 {
 	struct f2fs_crypto_ctx *ctx = NULL;
 	unsigned long flags;
 	struct f2fs_crypt_info *ci = F2FS_I(inode)->i_crypt_info;

 	if (ci == NULL)
 		return ERR_PTR(-ENOKEY);

 	/*
 	 * We first try getting the ctx from a free list because in
 	 * the common case the ctx will have an allocated and
 	 * initialized crypto tfm, so it's probably a worthwhile
 	 * optimization. For the bounce page, we first try getting it
 	 * from the kernel allocator because that's just about as fast
 	 * as getting it from a list and because a cache of free pages
 	 * should generally be a "last resort" option for a filesystem
 	 * to be able to do its job.
 	 */
 	spin_lock_irqsave(&f2fs_crypto_ctx_lock, flags);
 	ctx = list_first_entry_or_null(&f2fs_free_crypto_ctxs,
 					struct f2fs_crypto_ctx, free_list);
 	if (ctx)
 		list_del(&ctx->free_list);
 	spin_unlock_irqrestore(&f2fs_crypto_ctx_lock, flags);
 	if (!ctx) {
 		ctx = kmem_cache_zalloc(f2fs_crypto_ctx_cachep, GFP_NOFS);
 		if (!ctx)
 			return ERR_PTR(-ENOMEM);
 		ctx->flags |= F2FS_CTX_REQUIRES_FREE_ENCRYPT_FL;
 	} else {
 		ctx->flags &= ~F2FS_CTX_REQUIRES_FREE_ENCRYPT_FL;
 	}
 	ctx->flags &= ~F2FS_WRITE_PATH_FL;
 	return ctx;
 }

 /*
  * Call f2fs_decrypt on every single page, reusing the encryption
  * context.
  */
 static void completion_pages(struct work_struct *work)
 {
 	struct f2fs_crypto_ctx *ctx =
 		container_of(work, struct f2fs_crypto_ctx, r.work);
 	struct bio *bio = ctx->r.bio;
 	struct bio_vec *bv;
 	int i;

 	bio_for_each_segment_all(bv, bio, i) {
 		struct page *page = bv->bv_page;
 		int ret = f2fs_decrypt(ctx, page);

 		if (ret) {
 			WARN_ON_ONCE(1);
 			SetPageError(page);
 		} else
 			SetPageUptodate(page);
 		unlock_page(page);
 	}
 	f2fs_release_crypto_ctx(ctx);
 	bio_put(bio);
 }

 void f2fs_end_io_crypto_work(struct f2fs_crypto_ctx *ctx, struct bio *bio)
 {
 	INIT_WORK(&ctx->r.work, completion_pages);
 	ctx->r.bio = bio;
 	queue_work(f2fs_read_workqueue, &ctx->r.work);
 }

 static void f2fs_crypto_destroy(void)
 {
 	struct f2fs_crypto_ctx *pos, *n;

 	list_for_each_entry_safe(pos, n, &f2fs_free_crypto_ctxs, free_list)
 		kmem_cache_free(f2fs_crypto_ctx_cachep, pos);
 	INIT_LIST_HEAD(&f2fs_free_crypto_ctxs);
 	if (f2fs_bounce_page_pool)
 		mempool_destroy(f2fs_bounce_page_pool);
 	f2fs_bounce_page_pool = NULL;
 }

 /**
  * f2fs_crypto_initialize() - Set up for f2fs encryption.
  *
  * We only call this when we start accessing encrypted files, since it
  * results in memory getting allocated that wouldn't otherwise be used.
  *
  * Return: Zero on success, non-zero otherwise.
  */
 int f2fs_crypto_initialize(void)
 {
 	int i, res = -ENOMEM;

 	if (f2fs_bounce_page_pool)
 		return 0;

 	mutex_lock(&crypto_init);
 	if (f2fs_bounce_page_pool)
 		goto already_initialized;

 	for (i = 0; i < num_prealloc_crypto_ctxs; i++) {
 		struct f2fs_crypto_ctx *ctx;

 		ctx = kmem_cache_zalloc(f2fs_crypto_ctx_cachep, GFP_KERNEL);
 		if (!ctx)
 			goto fail;
 		list_add(&ctx->free_list, &f2fs_free_crypto_ctxs);
 	}

 	/* must be allocated at the last step to avoid race condition above */
 	f2fs_bounce_page_pool =
 		mempool_create_page_pool(num_prealloc_crypto_pages, 0);
 	if (!f2fs_bounce_page_pool)
 		goto fail;

 already_initialized:
 	mutex_unlock(&crypto_init);
 	return 0;
 fail:
 	f2fs_crypto_destroy();
 	mutex_unlock(&crypto_init);
 	return res;
 }

 /**
  * f2fs_exit_crypto() - Shutdown the f2fs encryption system
  */
 void f2fs_exit_crypto(void)
 {
 	f2fs_crypto_destroy();

 	if (f2fs_read_workqueue)
 		destroy_workqueue(f2fs_read_workqueue);
 	if (f2fs_crypto_ctx_cachep)
 		kmem_cache_destroy(f2fs_crypto_ctx_cachep);
 	if (f2fs_crypt_info_cachep)
 		kmem_cache_destroy(f2fs_crypt_info_cachep);
 }

 int __init f2fs_init_crypto(void)
 {
 	int res = -ENOMEM;

 	f2fs_read_workqueue = alloc_workqueue("f2fs_crypto", WQ_HIGHPRI, 0);
 	if (!f2fs_read_workqueue)
 		goto fail;

 	f2fs_crypto_ctx_cachep = KMEM_CACHE(f2fs_crypto_ctx,
 						SLAB_RECLAIM_ACCOUNT);
 	if (!f2fs_crypto_ctx_cachep)
 		goto fail;

 	f2fs_crypt_info_cachep = KMEM_CACHE(f2fs_crypt_info,
 						SLAB_RECLAIM_ACCOUNT);
 	if (!f2fs_crypt_info_cachep)
 		goto fail;

 	return 0;
 fail:
 	f2fs_exit_crypto();
 	return res;
 }

 void f2fs_restore_and_release_control_page(struct page **page)
 {
 	struct f2fs_crypto_ctx *ctx;
 	struct page *bounce_page;

 	/* The bounce data pages are unmapped. */
 	if ((*page)->mapping)
 		return;

 	/* The bounce data page is unmapped. */
 	bounce_page = *page;
 	ctx = (struct f2fs_crypto_ctx *)page_private(bounce_page);

 	/* restore control page */
 	*page = ctx->w.control_page;

 	f2fs_restore_control_page(bounce_page);
 }

 void f2fs_restore_control_page(struct page *data_page)
 {
 	struct f2fs_crypto_ctx *ctx =
 		(struct f2fs_crypto_ctx *)page_private(data_page);

 	set_page_private(data_page, (unsigned long)NULL);
 	ClearPagePrivate(data_page);
 	unlock_page(data_page);
 	f2fs_release_crypto_ctx(ctx);
 }

 /**
  * f2fs_crypt_complete() - The completion callback for page encryption
  * @req: The asynchronous encryption request context
  * @res: The result of the encryption operation
  */
 static void f2fs_crypt_complete(struct crypto_async_request *req, int res)
 {
 	struct f2fs_completion_result *ecr = req->data;

 	if (res == -EINPROGRESS)
 		return;
 	ecr->res = res;
 	complete(&ecr->completion);
 }

 typedef enum {
 	F2FS_DECRYPT = 0,
 	F2FS_ENCRYPT,
 } f2fs_direction_t;

 static int f2fs_page_crypto(struct f2fs_crypto_ctx *ctx,
 				struct inode *inode,
 				f2fs_direction_t rw,
 				pgoff_t index,
 				struct page *src_page,
 				struct page *dest_page)
 {
 	u8 xts_tweak[F2FS_XTS_TWEAK_SIZE];
 	struct ablkcipher_request *req = NULL;
 	DECLARE_F2FS_COMPLETION_RESULT(ecr);
 	struct scatterlist dst, src;
 	struct f2fs_crypt_info *ci = F2FS_I(inode)->i_crypt_info;
 	struct crypto_ablkcipher *tfm = ci->ci_ctfm;
 	int res = 0;

 	req = ablkcipher_request_alloc(tfm, GFP_NOFS);
 	if (!req) {
 		printk_ratelimited(KERN_ERR
 				"%s: crypto_request_alloc() failed\n",
 				__func__);
 		return -ENOMEM;
 	}
 	ablkcipher_request_set_callback(
 		req, CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
 		f2fs_crypt_complete, &ecr);

 	BUILD_BUG_ON(F2FS_XTS_TWEAK_SIZE < sizeof(index));
 	memcpy(xts_tweak, &index, sizeof(index));
 	memset(&xts_tweak[sizeof(index)], 0,
 			F2FS_XTS_TWEAK_SIZE - sizeof(index));

 	sg_init_table(&dst, 1);
 	sg_set_page(&dst, dest_page, PAGE_CACHE_SIZE, 0);
 	sg_init_table(&src, 1);
 	sg_set_page(&src, src_page, PAGE_CACHE_SIZE, 0);
 	ablkcipher_request_set_crypt(req, &src, &dst, PAGE_CACHE_SIZE,
 					xts_tweak);
 	if (rw == F2FS_DECRYPT)
 		res = crypto_ablkcipher_decrypt(req);
 	else
 		res = crypto_ablkcipher_encrypt(req);
 	if (res == -EINPROGRESS || res == -EBUSY) {
 		BUG_ON(req->base.data != &ecr);
 		wait_for_completion(&ecr.completion);
 		res = ecr.res;
 	}
 	ablkcipher_request_free(req);
 	if (res) {
 		printk_ratelimited(KERN_ERR
 			"%s: crypto_ablkcipher_encrypt() returned %d\n",
 			__func__, res);
 		return res;
 	}
 	return 0;
 }

 static struct page *alloc_bounce_page(struct f2fs_crypto_ctx *ctx)
 {
 	ctx->w.bounce_page = mempool_alloc(f2fs_bounce_page_pool, GFP_NOWAIT);
 	if (ctx->w.bounce_page == NULL)
 		return ERR_PTR(-ENOMEM);
 	ctx->flags |= F2FS_WRITE_PATH_FL;
 	return ctx->w.bounce_page;
 }

 /**
  * f2fs_encrypt() - Encrypts a page
  * @inode:          The inode for which the encryption should take place
  * @plaintext_page: The page to encrypt. Must be locked.
  *
  * Allocates a ciphertext page and encrypts plaintext_page into it using the ctx
  * encryption context.
  *
  * Called on the page write path.  The caller must call
  * f2fs_restore_control_page() on the returned ciphertext page to
  * release the bounce buffer and the encryption context.
  *
  * Return: An allocated page with the encrypted content on success. Else, an
  * error value or NULL.
  */
 struct page *f2fs_encrypt(struct inode *inode,
 			  struct page *plaintext_page)
 {
 	struct f2fs_crypto_ctx *ctx;
 	struct page *ciphertext_page = NULL;
 	int err;

 	BUG_ON(!PageLocked(plaintext_page));

 	ctx = f2fs_get_crypto_ctx(inode);
 	if (IS_ERR(ctx))
 		return (struct page *)ctx;

 	/* The encryption operation will require a bounce page. */
 	ciphertext_page = alloc_bounce_page(ctx);
 	if (IS_ERR(ciphertext_page))
 		goto err_out;

 	ctx->w.control_page = plaintext_page;
 	err = f2fs_page_crypto(ctx, inode, F2FS_ENCRYPT, plaintext_page->index,
 					plaintext_page, ciphertext_page);
 	if (err) {
 		ciphertext_page = ERR_PTR(err);
 		goto err_out;
 	}

 	SetPagePrivate(ciphertext_page);
 	set_page_private(ciphertext_page, (unsigned long)ctx);
 	lock_page(ciphertext_page);
 	return ciphertext_page;

 err_out:
 	f2fs_release_crypto_ctx(ctx);
 	return ciphertext_page;
 }

 /**
  * f2fs_decrypt() - Decrypts a page in-place
  * @ctx:  The encryption context.
  * @page: The page to decrypt. Must be locked.
  *
  * Decrypts page in-place using the ctx encryption context.
  *
  * Called from the read completion callback.
  *
  * Return: Zero on success, non-zero otherwise.
  */
 int f2fs_decrypt(struct f2fs_crypto_ctx *ctx, struct page *page)
 {
 	BUG_ON(!PageLocked(page));

 	return f2fs_page_crypto(ctx, page->mapping->host,
 				F2FS_DECRYPT, page->index, page, page);
 }

 /*
  * Convenience function which takes care of allocating and
  * deallocating the encryption context
  */
 int f2fs_decrypt_one(struct inode *inode, struct page *page)
 {
 	struct f2fs_crypto_ctx *ctx = f2fs_get_crypto_ctx(inode);
 	int ret;

 	if (IS_ERR(ctx))
 		return PTR_ERR(ctx);
 	ret = f2fs_decrypt(ctx, page);
 	f2fs_release_crypto_ctx(ctx);
 	return ret;
 }

 bool f2fs_valid_contents_enc_mode(uint32_t mode)
 {
 	return (mode == F2FS_ENCRYPTION_MODE_AES_256_XTS);
 }

 /**
  * f2fs_validate_encryption_key_size() - Validate the encryption key size
  * @mode: The key mode.
  * @size: The key size to validate.
  *
  * Return: The validated key size for @mode. Zero if invalid.
  */
 uint32_t f2fs_validate_encryption_key_size(uint32_t mode, uint32_t size)
 {
 	if (size == f2fs_encryption_key_size(mode))
 		return size;
 	return 0;
 }
	/*
	* linux/fs/f2fs/crypto.c
	*
	* Copied from linux/fs/ext4/crypto.c
	*
	* Copyright (C) 2015, Google, Inc.
	* Copyright (C) 2015, Motorola Mobility
	*
	* This contains encryption functions for f2fs
	*
	* Written by Michael Halcrow, 2014.
	*
	* Filename encryption additions
	* Uday Savagaonkar, 2014
	* Encryption policy handling additions
	* Ildar Muslukhov, 2014
	* Remove ext4_encrypted_zeroout(),
	* add f2fs_restore_and_release_control_page()
	* Jaegeuk Kim, 2015.
	*
	* This has not yet undergone a rigorous security audit.
	*
	* The usage of AES-XTS should conform to recommendations in NIST
	* Special Publication 800-38E and IEEE P1619/D16.
	*/
	#include <crypto/hash.h>
	#include <crypto/sha.h>
	#include <keys/user-type.h>
	#include <keys/encrypted-type.h>
	#include <linux/crypto.h>
	#include <linux/ecryptfs.h>
	#include <linux/gfp.h>
	#include <linux/kernel.h>
	#include <linux/key.h>
	#include <linux/list.h>
	#include <linux/mempool.h>
	#include <linux/module.h>
	#include <linux/mutex.h>
	#include <linux/random.h>
	#include <linux/scatterlist.h>
	#include <linux/spinlock_types.h>
	#include <linux/f2fs_fs.h>
	#include <linux/ratelimit.h>
	#include <linux/bio.h>

	#include "f2fs.h"
	#include "xattr.h"

	/* Encryption added and removed here! (L: */

	static unsigned int num_prealloc_crypto_pages = 32;
	static unsigned int num_prealloc_crypto_ctxs = 128;

	module_param(num_prealloc_crypto_pages, uint, 0444);
	MODULE_PARM_DESC(num_prealloc_crypto_pages,
	"Number of crypto pages to preallocate");
	module_param(num_prealloc_crypto_ctxs, uint, 0444);
	MODULE_PARM_DESC(num_prealloc_crypto_ctxs,
	"Number of crypto contexts to preallocate");

	static mempool_t *f2fs_bounce_page_pool;

	static LIST_HEAD(f2fs_free_crypto_ctxs);
	static DEFINE_SPINLOCK(f2fs_crypto_ctx_lock);

	static struct workqueue_struct *f2fs_read_workqueue;
	static DEFINE_MUTEX(crypto_init);

	static struct kmem_cache *f2fs_crypto_ctx_cachep;
	struct kmem_cache *f2fs_crypt_info_cachep;

	/**
	* f2fs_release_crypto_ctx() - Releases an encryption context
	* @ctx: The encryption context to release.
	*
	* If the encryption context was allocated from the pre-allocated pool, returns
	* it to that pool. Else, frees it.
	*
	* If there's a bounce page in the context, this frees that.
	*/
	void f2fs_release_crypto_ctx(struct f2fs_crypto_ctx *ctx)
	{
	unsigned long flags;

	if (ctx->flags & F2FS_WRITE_PATH_FL && ctx->w.bounce_page) {
	mempool_free(ctx->w.bounce_page, f2fs_bounce_page_pool);
	ctx->w.bounce_page = NULL;
	}
	ctx->w.control_page = NULL;
	if (ctx->flags & F2FS_CTX_REQUIRES_FREE_ENCRYPT_FL) {
	kmem_cache_free(f2fs_crypto_ctx_cachep, ctx);
	} else {
	spin_lock_irqsave(&f2fs_crypto_ctx_lock, flags);
	list_add(&ctx->free_list, &f2fs_free_crypto_ctxs);
	spin_unlock_irqrestore(&f2fs_crypto_ctx_lock, flags);
	}
	}

	/**
	* f2fs_get_crypto_ctx() - Gets an encryption context
	* @inode: The inode for which we are doing the crypto
	*
	* Allocates and initializes an encryption context.
	*
	* Return: An allocated and initialized encryption context on success; error
	* value or NULL otherwise.
	*/
	struct f2fs_crypto_ctx f2fs_get_crypto_ctx(struct inode inode)
	{
	struct f2fs_crypto_ctx *ctx = NULL;
	unsigned long flags;
	struct f2fs_crypt_info *ci = F2FS_I(inode)->i_crypt_info;

	if (ci == NULL)
	return ERR_PTR(-ENOKEY);

	/*
	* We first try getting the ctx from a free list because in
	* the common case the ctx will have an allocated and
	* initialized crypto tfm, so it's probably a worthwhile
	* optimization. For the bounce page, we first try getting it
	* from the kernel allocator because that's just about as fast
	* as getting it from a list and because a cache of free pages
	* should generally be a "last resort" option for a filesystem
	* to be able to do its job.
	*/
	spin_lock_irqsave(&f2fs_crypto_ctx_lock, flags);
	ctx = list_first_entry_or_null(&f2fs_free_crypto_ctxs,
	struct f2fs_crypto_ctx, free_list);
	if (ctx)
	list_del(&ctx->free_list);
	spin_unlock_irqrestore(&f2fs_crypto_ctx_lock, flags);
	if (!ctx) {
	ctx = kmem_cache_zalloc(f2fs_crypto_ctx_cachep, GFP_NOFS);
	if (!ctx)
	return ERR_PTR(-ENOMEM);
	ctx->flags \|= F2FS_CTX_REQUIRES_FREE_ENCRYPT_FL;
	} else {
	ctx->flags &= ~F2FS_CTX_REQUIRES_FREE_ENCRYPT_FL;
	}
	ctx->flags &= ~F2FS_WRITE_PATH_FL;
	return ctx;
	}

	/*
	* Call f2fs_decrypt on every single page, reusing the encryption
	* context.
	*/
	static void completion_pages(struct work_struct *work)
	{
	struct f2fs_crypto_ctx *ctx =
	container_of(work, struct f2fs_crypto_ctx, r.work);
	struct bio *bio = ctx->r.bio;
	struct bio_vec *bv;
	int i;

	bio_for_each_segment_all(bv, bio, i) {
	struct page *page = bv->bv_page;
	int ret = f2fs_decrypt(ctx, page);

	if (ret) {
	WARN_ON_ONCE(1);
	SetPageError(page);
	} else
	SetPageUptodate(page);
	unlock_page(page);
	}
	f2fs_release_crypto_ctx(ctx);
	bio_put(bio);
	}

	void f2fs_end_io_crypto_work(struct f2fs_crypto_ctx ctx, struct bio bio)
	{
	INIT_WORK(&ctx->r.work, completion_pages);
	ctx->r.bio = bio;
	queue_work(f2fs_read_workqueue, &ctx->r.work);
	}

	static void f2fs_crypto_destroy(void)
	{
	struct f2fs_crypto_ctx pos, n;

	list_for_each_entry_safe(pos, n, &f2fs_free_crypto_ctxs, free_list)
	kmem_cache_free(f2fs_crypto_ctx_cachep, pos);
	INIT_LIST_HEAD(&f2fs_free_crypto_ctxs);
	if (f2fs_bounce_page_pool)
	mempool_destroy(f2fs_bounce_page_pool);
	f2fs_bounce_page_pool = NULL;
	}

	/**
	* f2fs_crypto_initialize() - Set up for f2fs encryption.
	*
	* We only call this when we start accessing encrypted files, since it
	* results in memory getting allocated that wouldn't otherwise be used.
	*
	* Return: Zero on success, non-zero otherwise.
	*/
	int f2fs_crypto_initialize(void)
	{
	int i, res = -ENOMEM;

	if (f2fs_bounce_page_pool)
	return 0;

	mutex_lock(&crypto_init);
	if (f2fs_bounce_page_pool)
	goto already_initialized;

	for (i = 0; i < num_prealloc_crypto_ctxs; i++) {
	struct f2fs_crypto_ctx *ctx;

	ctx = kmem_cache_zalloc(f2fs_crypto_ctx_cachep, GFP_KERNEL);
	if (!ctx)
	goto fail;
	list_add(&ctx->free_list, &f2fs_free_crypto_ctxs);
	}

	/* must be allocated at the last step to avoid race condition above */
	f2fs_bounce_page_pool =
	mempool_create_page_pool(num_prealloc_crypto_pages, 0);
	if (!f2fs_bounce_page_pool)
	goto fail;

	already_initialized:
	mutex_unlock(&crypto_init);
	return 0;
	fail:
	f2fs_crypto_destroy();
	mutex_unlock(&crypto_init);
	return res;
	}

	/**
	* f2fs_exit_crypto() - Shutdown the f2fs encryption system
	*/
	void f2fs_exit_crypto(void)
	{
	f2fs_crypto_destroy();

	if (f2fs_read_workqueue)
	destroy_workqueue(f2fs_read_workqueue);
	if (f2fs_crypto_ctx_cachep)
	kmem_cache_destroy(f2fs_crypto_ctx_cachep);
	if (f2fs_crypt_info_cachep)
	kmem_cache_destroy(f2fs_crypt_info_cachep);
	}

	int __init f2fs_init_crypto(void)
	{
	int res = -ENOMEM;

	f2fs_read_workqueue = alloc_workqueue("f2fs_crypto", WQ_HIGHPRI, 0);
	if (!f2fs_read_workqueue)
	goto fail;

	f2fs_crypto_ctx_cachep = KMEM_CACHE(f2fs_crypto_ctx,
	SLAB_RECLAIM_ACCOUNT);
	if (!f2fs_crypto_ctx_cachep)
	goto fail;

	f2fs_crypt_info_cachep = KMEM_CACHE(f2fs_crypt_info,
	SLAB_RECLAIM_ACCOUNT);
	if (!f2fs_crypt_info_cachep)
	goto fail;

	return 0;
	fail:
	f2fs_exit_crypto();
	return res;
	}

	void f2fs_restore_and_release_control_page(struct page **page)
	{
	struct f2fs_crypto_ctx *ctx;
	struct page *bounce_page;

	/* The bounce data pages are unmapped. */
	if ((*page)->mapping)
	return;

	/* The bounce data page is unmapped. */
	bounce_page = *page;
	ctx = (struct f2fs_crypto_ctx *)page_private(bounce_page);

	/* restore control page */
	*page = ctx->w.control_page;

	f2fs_restore_control_page(bounce_page);
	}

	void f2fs_restore_control_page(struct page *data_page)
	{
	struct f2fs_crypto_ctx *ctx =
	(struct f2fs_crypto_ctx *)page_private(data_page);

	set_page_private(data_page, (unsigned long)NULL);
	ClearPagePrivate(data_page);
	unlock_page(data_page);
	f2fs_release_crypto_ctx(ctx);
	}

	/**
	* f2fs_crypt_complete() - The completion callback for page encryption
	* @req: The asynchronous encryption request context
	* @res: The result of the encryption operation
	*/
	static void f2fs_crypt_complete(struct crypto_async_request *req, int res)
	{
	struct f2fs_completion_result *ecr = req->data;

	if (res == -EINPROGRESS)
	return;
	ecr->res = res;
	complete(&ecr->completion);
	}

	typedef enum {
	F2FS_DECRYPT = 0,
	F2FS_ENCRYPT,
	} f2fs_direction_t;

	static int f2fs_page_crypto(struct f2fs_crypto_ctx *ctx,
	struct inode *inode,
	f2fs_direction_t rw,
	pgoff_t index,
	struct page *src_page,
	struct page *dest_page)
	{
	u8 xts_tweak[F2FS_XTS_TWEAK_SIZE];
	struct ablkcipher_request *req = NULL;
	DECLARE_F2FS_COMPLETION_RESULT(ecr);
	struct scatterlist dst, src;
	struct f2fs_crypt_info *ci = F2FS_I(inode)->i_crypt_info;
	struct crypto_ablkcipher *tfm = ci->ci_ctfm;
	int res = 0;

	req = ablkcipher_request_alloc(tfm, GFP_NOFS);
	if (!req) {
	printk_ratelimited(KERN_ERR
	"%s: crypto_request_alloc() failed\n",
	__func__);
	return -ENOMEM;
	}
	ablkcipher_request_set_callback(
	req, CRYPTO_TFM_REQ_MAY_BACKLOG \| CRYPTO_TFM_REQ_MAY_SLEEP,
	f2fs_crypt_complete, &ecr);

	BUILD_BUG_ON(F2FS_XTS_TWEAK_SIZE < sizeof(index));
	memcpy(xts_tweak, &index, sizeof(index));
	memset(&xts_tweak[sizeof(index)], 0,
	F2FS_XTS_TWEAK_SIZE - sizeof(index));

	sg_init_table(&dst, 1);
	sg_set_page(&dst, dest_page, PAGE_CACHE_SIZE, 0);
	sg_init_table(&src, 1);
	sg_set_page(&src, src_page, PAGE_CACHE_SIZE, 0);
	ablkcipher_request_set_crypt(req, &src, &dst, PAGE_CACHE_SIZE,
	xts_tweak);
	if (rw == F2FS_DECRYPT)
	res = crypto_ablkcipher_decrypt(req);
	else
	res = crypto_ablkcipher_encrypt(req);
	if (res == -EINPROGRESS \|\| res == -EBUSY) {
	BUG_ON(req->base.data != &ecr);
	wait_for_completion(&ecr.completion);
	res = ecr.res;
	}
	ablkcipher_request_free(req);
	if (res) {
	printk_ratelimited(KERN_ERR
	"%s: crypto_ablkcipher_encrypt() returned %d\n",
	__func__, res);
	return res;
	}
	return 0;
	}

	static struct page alloc_bounce_page(struct f2fs_crypto_ctx ctx)
	{
	ctx->w.bounce_page = mempool_alloc(f2fs_bounce_page_pool, GFP_NOWAIT);
	if (ctx->w.bounce_page == NULL)
	return ERR_PTR(-ENOMEM);
	ctx->flags \|= F2FS_WRITE_PATH_FL;
	return ctx->w.bounce_page;
	}

	/**
	* f2fs_encrypt() - Encrypts a page
	* @inode: The inode for which the encryption should take place
	* @plaintext_page: The page to encrypt. Must be locked.
	*
	* Allocates a ciphertext page and encrypts plaintext_page into it using the ctx
	* encryption context.
	*
	* Called on the page write path. The caller must call
	* f2fs_restore_control_page() on the returned ciphertext page to
	* release the bounce buffer and the encryption context.
	*
	* Return: An allocated page with the encrypted content on success. Else, an
	* error value or NULL.
	*/
	struct page f2fs_encrypt(struct inode inode,
	struct page *plaintext_page)
	{
	struct f2fs_crypto_ctx *ctx;
	struct page *ciphertext_page = NULL;
	int err;

	BUG_ON(!PageLocked(plaintext_page));

	ctx = f2fs_get_crypto_ctx(inode);
	if (IS_ERR(ctx))
	return (struct page *)ctx;

	/* The encryption operation will require a bounce page. */
	ciphertext_page = alloc_bounce_page(ctx);
	if (IS_ERR(ciphertext_page))
	goto err_out;

	ctx->w.control_page = plaintext_page;
	err = f2fs_page_crypto(ctx, inode, F2FS_ENCRYPT, plaintext_page->index,
	plaintext_page, ciphertext_page);
	if (err) {
	ciphertext_page = ERR_PTR(err);
	goto err_out;
	}

	SetPagePrivate(ciphertext_page);
	set_page_private(ciphertext_page, (unsigned long)ctx);
	lock_page(ciphertext_page);
	return ciphertext_page;

	err_out:
	f2fs_release_crypto_ctx(ctx);
	return ciphertext_page;
	}

	/**
	* f2fs_decrypt() - Decrypts a page in-place
	* @ctx: The encryption context.
	* @page: The page to decrypt. Must be locked.
	*
	* Decrypts page in-place using the ctx encryption context.
	*
	* Called from the read completion callback.
	*
	* Return: Zero on success, non-zero otherwise.
	*/
	int f2fs_decrypt(struct f2fs_crypto_ctx ctx, struct page page)
	{
	BUG_ON(!PageLocked(page));

	return f2fs_page_crypto(ctx, page->mapping->host,
	F2FS_DECRYPT, page->index, page, page);
	}

	/*
	* Convenience function which takes care of allocating and
	* deallocating the encryption context
	*/
	int f2fs_decrypt_one(struct inode inode, struct page page)
	{
	struct f2fs_crypto_ctx *ctx = f2fs_get_crypto_ctx(inode);
	int ret;

	if (IS_ERR(ctx))
	return PTR_ERR(ctx);
	ret = f2fs_decrypt(ctx, page);
	f2fs_release_crypto_ctx(ctx);
	return ret;
	}

	bool f2fs_valid_contents_enc_mode(uint32_t mode)
	{
	return (mode == F2FS_ENCRYPTION_MODE_AES_256_XTS);
	}

	/**
	* f2fs_validate_encryption_key_size() - Validate the encryption key size
	* @mode: The key mode.
	* @size: The key size to validate.
	*
	* Return: The validated key size for @mode. Zero if invalid.
	*/
	uint32_t f2fs_validate_encryption_key_size(uint32_t mode, uint32_t size)
	{
	if (size == f2fs_encryption_key_size(mode))
	return size;
	return 0;
	}