cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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verity.c (8353B)


      1// SPDX-License-Identifier: GPL-2.0
      2/*
      3 * fs/f2fs/verity.c: fs-verity support for f2fs
      4 *
      5 * Copyright 2019 Google LLC
      6 */
      7
      8/*
      9 * Implementation of fsverity_operations for f2fs.
     10 *
     11 * Like ext4, f2fs stores the verity metadata (Merkle tree and
     12 * fsverity_descriptor) past the end of the file, starting at the first 64K
     13 * boundary beyond i_size.  This approach works because (a) verity files are
     14 * readonly, and (b) pages fully beyond i_size aren't visible to userspace but
     15 * can be read/written internally by f2fs with only some relatively small
     16 * changes to f2fs.  Extended attributes cannot be used because (a) f2fs limits
     17 * the total size of an inode's xattr entries to 4096 bytes, which wouldn't be
     18 * enough for even a single Merkle tree block, and (b) f2fs encryption doesn't
     19 * encrypt xattrs, yet the verity metadata *must* be encrypted when the file is
     20 * because it contains hashes of the plaintext data.
     21 *
     22 * Using a 64K boundary rather than a 4K one keeps things ready for
     23 * architectures with 64K pages, and it doesn't necessarily waste space on-disk
     24 * since there can be a hole between i_size and the start of the Merkle tree.
     25 */
     26
     27#include <linux/f2fs_fs.h>
     28
     29#include "f2fs.h"
     30#include "xattr.h"
     31
     32#define F2FS_VERIFY_VER	(1)
     33
     34static inline loff_t f2fs_verity_metadata_pos(const struct inode *inode)
     35{
     36	return round_up(inode->i_size, 65536);
     37}
     38
     39/*
     40 * Read some verity metadata from the inode.  __vfs_read() can't be used because
     41 * we need to read beyond i_size.
     42 */
     43static int pagecache_read(struct inode *inode, void *buf, size_t count,
     44			  loff_t pos)
     45{
     46	while (count) {
     47		size_t n = min_t(size_t, count,
     48				 PAGE_SIZE - offset_in_page(pos));
     49		struct page *page;
     50		void *addr;
     51
     52		page = read_mapping_page(inode->i_mapping, pos >> PAGE_SHIFT,
     53					 NULL);
     54		if (IS_ERR(page))
     55			return PTR_ERR(page);
     56
     57		addr = kmap_atomic(page);
     58		memcpy(buf, addr + offset_in_page(pos), n);
     59		kunmap_atomic(addr);
     60
     61		put_page(page);
     62
     63		buf += n;
     64		pos += n;
     65		count -= n;
     66	}
     67	return 0;
     68}
     69
     70/*
     71 * Write some verity metadata to the inode for FS_IOC_ENABLE_VERITY.
     72 * kernel_write() can't be used because the file descriptor is readonly.
     73 */
     74static int pagecache_write(struct inode *inode, const void *buf, size_t count,
     75			   loff_t pos)
     76{
     77	struct address_space *mapping = inode->i_mapping;
     78	const struct address_space_operations *aops = mapping->a_ops;
     79
     80	if (pos + count > inode->i_sb->s_maxbytes)
     81		return -EFBIG;
     82
     83	while (count) {
     84		size_t n = min_t(size_t, count,
     85				 PAGE_SIZE - offset_in_page(pos));
     86		struct page *page;
     87		void *fsdata;
     88		void *addr;
     89		int res;
     90
     91		res = aops->write_begin(NULL, mapping, pos, n, &page, &fsdata);
     92		if (res)
     93			return res;
     94
     95		addr = kmap_atomic(page);
     96		memcpy(addr + offset_in_page(pos), buf, n);
     97		kunmap_atomic(addr);
     98
     99		res = aops->write_end(NULL, mapping, pos, n, n, page, fsdata);
    100		if (res < 0)
    101			return res;
    102		if (res != n)
    103			return -EIO;
    104
    105		buf += n;
    106		pos += n;
    107		count -= n;
    108	}
    109	return 0;
    110}
    111
    112/*
    113 * Format of f2fs verity xattr.  This points to the location of the verity
    114 * descriptor within the file data rather than containing it directly because
    115 * the verity descriptor *must* be encrypted when f2fs encryption is used.  But,
    116 * f2fs encryption does not encrypt xattrs.
    117 */
    118struct fsverity_descriptor_location {
    119	__le32 version;
    120	__le32 size;
    121	__le64 pos;
    122};
    123
    124static int f2fs_begin_enable_verity(struct file *filp)
    125{
    126	struct inode *inode = file_inode(filp);
    127	int err;
    128
    129	if (f2fs_verity_in_progress(inode))
    130		return -EBUSY;
    131
    132	if (f2fs_is_atomic_file(inode))
    133		return -EOPNOTSUPP;
    134
    135	/*
    136	 * Since the file was opened readonly, we have to initialize the quotas
    137	 * here and not rely on ->open() doing it.  This must be done before
    138	 * evicting the inline data.
    139	 */
    140	err = f2fs_dquot_initialize(inode);
    141	if (err)
    142		return err;
    143
    144	err = f2fs_convert_inline_inode(inode);
    145	if (err)
    146		return err;
    147
    148	set_inode_flag(inode, FI_VERITY_IN_PROGRESS);
    149	return 0;
    150}
    151
    152static int f2fs_end_enable_verity(struct file *filp, const void *desc,
    153				  size_t desc_size, u64 merkle_tree_size)
    154{
    155	struct inode *inode = file_inode(filp);
    156	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
    157	u64 desc_pos = f2fs_verity_metadata_pos(inode) + merkle_tree_size;
    158	struct fsverity_descriptor_location dloc = {
    159		.version = cpu_to_le32(F2FS_VERIFY_VER),
    160		.size = cpu_to_le32(desc_size),
    161		.pos = cpu_to_le64(desc_pos),
    162	};
    163	int err = 0, err2 = 0;
    164
    165	/*
    166	 * If an error already occurred (which fs/verity/ signals by passing
    167	 * desc == NULL), then only clean-up is needed.
    168	 */
    169	if (desc == NULL)
    170		goto cleanup;
    171
    172	/* Append the verity descriptor. */
    173	err = pagecache_write(inode, desc, desc_size, desc_pos);
    174	if (err)
    175		goto cleanup;
    176
    177	/*
    178	 * Write all pages (both data and verity metadata).  Note that this must
    179	 * happen before clearing FI_VERITY_IN_PROGRESS; otherwise pages beyond
    180	 * i_size won't be written properly.  For crash consistency, this also
    181	 * must happen before the verity inode flag gets persisted.
    182	 */
    183	err = filemap_write_and_wait(inode->i_mapping);
    184	if (err)
    185		goto cleanup;
    186
    187	/* Set the verity xattr. */
    188	err = f2fs_setxattr(inode, F2FS_XATTR_INDEX_VERITY,
    189			    F2FS_XATTR_NAME_VERITY, &dloc, sizeof(dloc),
    190			    NULL, XATTR_CREATE);
    191	if (err)
    192		goto cleanup;
    193
    194	/* Finally, set the verity inode flag. */
    195	file_set_verity(inode);
    196	f2fs_set_inode_flags(inode);
    197	f2fs_mark_inode_dirty_sync(inode, true);
    198
    199	clear_inode_flag(inode, FI_VERITY_IN_PROGRESS);
    200	return 0;
    201
    202cleanup:
    203	/*
    204	 * Verity failed to be enabled, so clean up by truncating any verity
    205	 * metadata that was written beyond i_size (both from cache and from
    206	 * disk) and clearing FI_VERITY_IN_PROGRESS.
    207	 *
    208	 * Taking i_gc_rwsem[WRITE] is needed to stop f2fs garbage collection
    209	 * from re-instantiating cached pages we are truncating (since unlike
    210	 * normal file accesses, garbage collection isn't limited by i_size).
    211	 */
    212	f2fs_down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
    213	truncate_inode_pages(inode->i_mapping, inode->i_size);
    214	err2 = f2fs_truncate(inode);
    215	if (err2) {
    216		f2fs_err(sbi, "Truncating verity metadata failed (errno=%d)",
    217			 err2);
    218		set_sbi_flag(sbi, SBI_NEED_FSCK);
    219	}
    220	f2fs_up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
    221	clear_inode_flag(inode, FI_VERITY_IN_PROGRESS);
    222	return err ?: err2;
    223}
    224
    225static int f2fs_get_verity_descriptor(struct inode *inode, void *buf,
    226				      size_t buf_size)
    227{
    228	struct fsverity_descriptor_location dloc;
    229	int res;
    230	u32 size;
    231	u64 pos;
    232
    233	/* Get the descriptor location */
    234	res = f2fs_getxattr(inode, F2FS_XATTR_INDEX_VERITY,
    235			    F2FS_XATTR_NAME_VERITY, &dloc, sizeof(dloc), NULL);
    236	if (res < 0 && res != -ERANGE)
    237		return res;
    238	if (res != sizeof(dloc) || dloc.version != cpu_to_le32(F2FS_VERIFY_VER)) {
    239		f2fs_warn(F2FS_I_SB(inode), "unknown verity xattr format");
    240		return -EINVAL;
    241	}
    242	size = le32_to_cpu(dloc.size);
    243	pos = le64_to_cpu(dloc.pos);
    244
    245	/* Get the descriptor */
    246	if (pos + size < pos || pos + size > inode->i_sb->s_maxbytes ||
    247	    pos < f2fs_verity_metadata_pos(inode) || size > INT_MAX) {
    248		f2fs_warn(F2FS_I_SB(inode), "invalid verity xattr");
    249		return -EFSCORRUPTED;
    250	}
    251	if (buf_size) {
    252		if (size > buf_size)
    253			return -ERANGE;
    254		res = pagecache_read(inode, buf, size, pos);
    255		if (res)
    256			return res;
    257	}
    258	return size;
    259}
    260
    261static struct page *f2fs_read_merkle_tree_page(struct inode *inode,
    262					       pgoff_t index,
    263					       unsigned long num_ra_pages)
    264{
    265	DEFINE_READAHEAD(ractl, NULL, NULL, inode->i_mapping, index);
    266	struct page *page;
    267
    268	index += f2fs_verity_metadata_pos(inode) >> PAGE_SHIFT;
    269
    270	page = find_get_page_flags(inode->i_mapping, index, FGP_ACCESSED);
    271	if (!page || !PageUptodate(page)) {
    272		if (page)
    273			put_page(page);
    274		else if (num_ra_pages > 1)
    275			page_cache_ra_unbounded(&ractl, num_ra_pages, 0);
    276		page = read_mapping_page(inode->i_mapping, index, NULL);
    277	}
    278	return page;
    279}
    280
    281static int f2fs_write_merkle_tree_block(struct inode *inode, const void *buf,
    282					u64 index, int log_blocksize)
    283{
    284	loff_t pos = f2fs_verity_metadata_pos(inode) + (index << log_blocksize);
    285
    286	return pagecache_write(inode, buf, 1 << log_blocksize, pos);
    287}
    288
    289const struct fsverity_operations f2fs_verityops = {
    290	.begin_enable_verity	= f2fs_begin_enable_verity,
    291	.end_enable_verity	= f2fs_end_enable_verity,
    292	.get_verity_descriptor	= f2fs_get_verity_descriptor,
    293	.read_merkle_tree_page	= f2fs_read_merkle_tree_page,
    294	.write_merkle_tree_block = f2fs_write_merkle_tree_block,
    295};