linux/drivers/md/dm-verity-fec.c

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/*
* Copyright (C) 2015 Google, Inc.
*
* Author: Sami Tolvanen <samitolvanen@google.com>
*
* 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 "dm-verity-fec.h"
#include <linux/math64.h>
#define DM_MSG_PREFIX "verity-fec"
/*
* If error correction has been configured, returns true.
*/
bool verity_fec_is_enabled(struct dm_verity *v)
{
return v->fec && v->fec->dev;
}
/*
* Return a pointer to dm_verity_fec_io after dm_verity_io and its variable
* length fields.
*/
static inline struct dm_verity_fec_io *fec_io(struct dm_verity_io *io)
{
return (struct dm_verity_fec_io *) verity_io_digest_end(io->v, io);
}
/*
* Return an interleaved offset for a byte in RS block.
*/
static inline u64 fec_interleave(struct dm_verity *v, u64 offset)
{
u32 mod;
mod = do_div(offset, v->fec->rsn);
return offset + mod * (v->fec->rounds << v->data_dev_block_bits);
}
/*
* Decode an RS block using Reed-Solomon.
*/
static int fec_decode_rs8(struct dm_verity *v, struct dm_verity_fec_io *fio,
u8 *data, u8 *fec, int neras)
{
int i;
uint16_t par[DM_VERITY_FEC_RSM - DM_VERITY_FEC_MIN_RSN];
for (i = 0; i < v->fec->roots; i++)
par[i] = fec[i];
return decode_rs8(fio->rs, data, par, v->fec->rsn, NULL, neras,
fio->erasures, 0, NULL);
}
/*
* Read error-correcting codes for the requested RS block. Returns a pointer
* to the data block. Caller is responsible for releasing buf.
*/
static u8 *fec_read_parity(struct dm_verity *v, u64 rsb, int index,
unsigned *offset, struct dm_buffer **buf)
{
u64 position, block;
u8 *res;
position = (index + rsb) * v->fec->roots;
block = position >> v->data_dev_block_bits;
*offset = (unsigned)(position - (block << v->data_dev_block_bits));
res = dm_bufio_read(v->fec->bufio, v->fec->start + block, buf);
if (unlikely(IS_ERR(res))) {
DMERR("%s: FEC %llu: parity read failed (block %llu): %ld",
v->data_dev->name, (unsigned long long)rsb,
(unsigned long long)(v->fec->start + block),
PTR_ERR(res));
*buf = NULL;
}
return res;
}
/* Loop over each preallocated buffer slot. */
#define fec_for_each_prealloc_buffer(__i) \
for (__i = 0; __i < DM_VERITY_FEC_BUF_PREALLOC; __i++)
/* Loop over each extra buffer slot. */
#define fec_for_each_extra_buffer(io, __i) \
for (__i = DM_VERITY_FEC_BUF_PREALLOC; __i < DM_VERITY_FEC_BUF_MAX; __i++)
/* Loop over each allocated buffer. */
#define fec_for_each_buffer(io, __i) \
for (__i = 0; __i < (io)->nbufs; __i++)
/* Loop over each RS block in each allocated buffer. */
#define fec_for_each_buffer_rs_block(io, __i, __j) \
fec_for_each_buffer(io, __i) \
for (__j = 0; __j < 1 << DM_VERITY_FEC_BUF_RS_BITS; __j++)
/*
* Return a pointer to the current RS block when called inside
* fec_for_each_buffer_rs_block.
*/
static inline u8 *fec_buffer_rs_block(struct dm_verity *v,
struct dm_verity_fec_io *fio,
unsigned i, unsigned j)
{
return &fio->bufs[i][j * v->fec->rsn];
}
/*
* Return an index to the current RS block when called inside
* fec_for_each_buffer_rs_block.
*/
static inline unsigned fec_buffer_rs_index(unsigned i, unsigned j)
{
return (i << DM_VERITY_FEC_BUF_RS_BITS) + j;
}
/*
* Decode all RS blocks from buffers and copy corrected bytes into fio->output
* starting from block_offset.
*/
static int fec_decode_bufs(struct dm_verity *v, struct dm_verity_fec_io *fio,
u64 rsb, int byte_index, unsigned block_offset,
int neras)
{
int r, corrected = 0, res;
struct dm_buffer *buf;
unsigned n, i, offset;
u8 *par, *block;
par = fec_read_parity(v, rsb, block_offset, &offset, &buf);
if (IS_ERR(par))
return PTR_ERR(par);
/*
* Decode the RS blocks we have in bufs. Each RS block results in
* one corrected target byte and consumes fec->roots parity bytes.
*/
fec_for_each_buffer_rs_block(fio, n, i) {
block = fec_buffer_rs_block(v, fio, n, i);
res = fec_decode_rs8(v, fio, block, &par[offset], neras);
if (res < 0) {
dm_bufio_release(buf);
r = res;
goto error;
}
corrected += res;
fio->output[block_offset] = block[byte_index];
block_offset++;
if (block_offset >= 1 << v->data_dev_block_bits)
goto done;
/* read the next block when we run out of parity bytes */
offset += v->fec->roots;
if (offset >= 1 << v->data_dev_block_bits) {
dm_bufio_release(buf);
par = fec_read_parity(v, rsb, block_offset, &offset, &buf);
if (unlikely(IS_ERR(par)))
return PTR_ERR(par);
}
}
done:
r = corrected;
error:
if (r < 0 && neras)
DMERR_LIMIT("%s: FEC %llu: failed to correct: %d",
v->data_dev->name, (unsigned long long)rsb, r);
else if (r > 0)
DMWARN_LIMIT("%s: FEC %llu: corrected %d errors",
v->data_dev->name, (unsigned long long)rsb, r);
return r;
}
/*
* Locate data block erasures using verity hashes.
*/
static int fec_is_erasure(struct dm_verity *v, struct dm_verity_io *io,
u8 *want_digest, u8 *data)
{
if (unlikely(verity_hash(v, verity_io_hash_desc(v, io),
data, 1 << v->data_dev_block_bits,
verity_io_real_digest(v, io))))
return 0;
return memcmp(verity_io_real_digest(v, io), want_digest,
v->digest_size) != 0;
}
/*
* Read data blocks that are part of the RS block and deinterleave as much as
* fits into buffers. Check for erasure locations if @neras is non-NULL.
*/
static int fec_read_bufs(struct dm_verity *v, struct dm_verity_io *io,
u64 rsb, u64 target, unsigned block_offset,
int *neras)
{
bool is_zero;
int i, j, target_index = -1;
struct dm_buffer *buf;
struct dm_bufio_client *bufio;
struct dm_verity_fec_io *fio = fec_io(io);
u64 block, ileaved;
u8 *bbuf, *rs_block;
u8 want_digest[v->digest_size];
unsigned n, k;
if (neras)
*neras = 0;
/*
* read each of the rsn data blocks that are part of the RS block, and
* interleave contents to available bufs
*/
for (i = 0; i < v->fec->rsn; i++) {
ileaved = fec_interleave(v, rsb * v->fec->rsn + i);
/*
* target is the data block we want to correct, target_index is
* the index of this block within the rsn RS blocks
*/
if (ileaved == target)
target_index = i;
block = ileaved >> v->data_dev_block_bits;
bufio = v->fec->data_bufio;
if (block >= v->data_blocks) {
block -= v->data_blocks;
/*
* blocks outside the area were assumed to contain
* zeros when encoding data was generated
*/
if (unlikely(block >= v->fec->hash_blocks))
continue;
block += v->hash_start;
bufio = v->bufio;
}
bbuf = dm_bufio_read(bufio, block, &buf);
if (unlikely(IS_ERR(bbuf))) {
DMWARN_LIMIT("%s: FEC %llu: read failed (%llu): %ld",
v->data_dev->name,
(unsigned long long)rsb,
(unsigned long long)block, PTR_ERR(bbuf));
/* assume the block is corrupted */
if (neras && *neras <= v->fec->roots)
fio->erasures[(*neras)++] = i;
continue;
}
/* locate erasures if the block is on the data device */
if (bufio == v->fec->data_bufio &&
verity_hash_for_block(v, io, block, want_digest,
&is_zero) == 0) {
/* skip known zero blocks entirely */
if (is_zero)
continue;
/*
* skip if we have already found the theoretical
* maximum number (i.e. fec->roots) of erasures
*/
if (neras && *neras <= v->fec->roots &&
fec_is_erasure(v, io, want_digest, bbuf))
fio->erasures[(*neras)++] = i;
}
/*
* deinterleave and copy the bytes that fit into bufs,
* starting from block_offset
*/
fec_for_each_buffer_rs_block(fio, n, j) {
k = fec_buffer_rs_index(n, j) + block_offset;
if (k >= 1 << v->data_dev_block_bits)
goto done;
rs_block = fec_buffer_rs_block(v, fio, n, j);
rs_block[i] = bbuf[k];
}
done:
dm_bufio_release(buf);
}
return target_index;
}
/*
* Allocate RS control structure and FEC buffers from preallocated mempools,
* and attempt to allocate as many extra buffers as available.
*/
static int fec_alloc_bufs(struct dm_verity *v, struct dm_verity_fec_io *fio)
{
unsigned n;
if (!fio->rs) {
fio->rs = mempool_alloc(v->fec->rs_pool, 0);
if (unlikely(!fio->rs)) {
DMERR("failed to allocate RS");
return -ENOMEM;
}
}
fec_for_each_prealloc_buffer(n) {
if (fio->bufs[n])
continue;
fio->bufs[n] = mempool_alloc(v->fec->prealloc_pool, GFP_NOIO);
if (unlikely(!fio->bufs[n])) {
DMERR("failed to allocate FEC buffer");
return -ENOMEM;
}
}
/* try to allocate the maximum number of buffers */
fec_for_each_extra_buffer(fio, n) {
if (fio->bufs[n])
continue;
fio->bufs[n] = mempool_alloc(v->fec->extra_pool, GFP_NOIO);
/* we can manage with even one buffer if necessary */
if (unlikely(!fio->bufs[n]))
break;
}
fio->nbufs = n;
if (!fio->output) {
fio->output = mempool_alloc(v->fec->output_pool, GFP_NOIO);
if (!fio->output) {
DMERR("failed to allocate FEC page");
return -ENOMEM;
}
}
return 0;
}
/*
* Initialize buffers and clear erasures. fec_read_bufs() assumes buffers are
* zeroed before deinterleaving.
*/
static void fec_init_bufs(struct dm_verity *v, struct dm_verity_fec_io *fio)
{
unsigned n;
fec_for_each_buffer(fio, n)
memset(fio->bufs[n], 0, v->fec->rsn << DM_VERITY_FEC_BUF_RS_BITS);
memset(fio->erasures, 0, sizeof(fio->erasures));
}
/*
* Decode all RS blocks in a single data block and return the target block
* (indicated by @offset) in fio->output. If @use_erasures is non-zero, uses
* hashes to locate erasures.
*/
static int fec_decode_rsb(struct dm_verity *v, struct dm_verity_io *io,
struct dm_verity_fec_io *fio, u64 rsb, u64 offset,
bool use_erasures)
{
int r, neras = 0;
unsigned pos;
r = fec_alloc_bufs(v, fio);
if (unlikely(r < 0))
return r;
for (pos = 0; pos < 1 << v->data_dev_block_bits; ) {
fec_init_bufs(v, fio);
r = fec_read_bufs(v, io, rsb, offset, pos,
use_erasures ? &neras : NULL);
if (unlikely(r < 0))
return r;
r = fec_decode_bufs(v, fio, rsb, r, pos, neras);
if (r < 0)
return r;
pos += fio->nbufs << DM_VERITY_FEC_BUF_RS_BITS;
}
/* Always re-validate the corrected block against the expected hash */
r = verity_hash(v, verity_io_hash_desc(v, io), fio->output,
1 << v->data_dev_block_bits,
verity_io_real_digest(v, io));
if (unlikely(r < 0))
return r;
if (memcmp(verity_io_real_digest(v, io), verity_io_want_digest(v, io),
v->digest_size)) {
DMERR_LIMIT("%s: FEC %llu: failed to correct (%d erasures)",
v->data_dev->name, (unsigned long long)rsb, neras);
return -EILSEQ;
}
return 0;
}
static int fec_bv_copy(struct dm_verity *v, struct dm_verity_io *io, u8 *data,
size_t len)
{
struct dm_verity_fec_io *fio = fec_io(io);
memcpy(data, &fio->output[fio->output_pos], len);
fio->output_pos += len;
return 0;
}
/*
* Correct errors in a block. Copies corrected block to dest if non-NULL,
* otherwise to a bio_vec starting from iter.
*/
int verity_fec_decode(struct dm_verity *v, struct dm_verity_io *io,
enum verity_block_type type, sector_t block, u8 *dest,
struct bvec_iter *iter)
{
int r;
struct dm_verity_fec_io *fio = fec_io(io);
u64 offset, res, rsb;
if (!verity_fec_is_enabled(v))
return -EOPNOTSUPP;
if (type == DM_VERITY_BLOCK_TYPE_METADATA)
block += v->data_blocks;
/*
* For RS(M, N), the continuous FEC data is divided into blocks of N
* bytes. Since block size may not be divisible by N, the last block
* is zero padded when decoding.
*
* Each byte of the block is covered by a different RS(M, N) code,
* and each code is interleaved over N blocks to make it less likely
* that bursty corruption will leave us in unrecoverable state.
*/
offset = block << v->data_dev_block_bits;
res = div64_u64(offset, v->fec->rounds << v->data_dev_block_bits);
/*
* The base RS block we can feed to the interleaver to find out all
* blocks required for decoding.
*/
rsb = offset - res * (v->fec->rounds << v->data_dev_block_bits);
/*
* Locating erasures is slow, so attempt to recover the block without
* them first. Do a second attempt with erasures if the corruption is
* bad enough.
*/
r = fec_decode_rsb(v, io, fio, rsb, offset, false);
if (r < 0) {
r = fec_decode_rsb(v, io, fio, rsb, offset, true);
if (r < 0)
return r;
}
if (dest)
memcpy(dest, fio->output, 1 << v->data_dev_block_bits);
else if (iter) {
fio->output_pos = 0;
r = verity_for_bv_block(v, io, iter, fec_bv_copy);
}
return r;
}
/*
* Clean up per-bio data.
*/
void verity_fec_finish_io(struct dm_verity_io *io)
{
unsigned n;
struct dm_verity_fec *f = io->v->fec;
struct dm_verity_fec_io *fio = fec_io(io);
if (!verity_fec_is_enabled(io->v))
return;
mempool_free(fio->rs, f->rs_pool);
fec_for_each_prealloc_buffer(n)
mempool_free(fio->bufs[n], f->prealloc_pool);
fec_for_each_extra_buffer(fio, n)
mempool_free(fio->bufs[n], f->extra_pool);
mempool_free(fio->output, f->output_pool);
}
/*
* Initialize per-bio data.
*/
void verity_fec_init_io(struct dm_verity_io *io)
{
struct dm_verity_fec_io *fio = fec_io(io);
if (!verity_fec_is_enabled(io->v))
return;
fio->rs = NULL;
memset(fio->bufs, 0, sizeof(fio->bufs));
fio->nbufs = 0;
fio->output = NULL;
}
/*
* Append feature arguments and values to the status table.
*/
unsigned verity_fec_status_table(struct dm_verity *v, unsigned sz,
char *result, unsigned maxlen)
{
if (!verity_fec_is_enabled(v))
return sz;
DMEMIT(" " DM_VERITY_OPT_FEC_DEV " %s "
DM_VERITY_OPT_FEC_BLOCKS " %llu "
DM_VERITY_OPT_FEC_START " %llu "
DM_VERITY_OPT_FEC_ROOTS " %d",
v->fec->dev->name,
(unsigned long long)v->fec->blocks,
(unsigned long long)v->fec->start,
v->fec->roots);
return sz;
}
void verity_fec_dtr(struct dm_verity *v)
{
struct dm_verity_fec *f = v->fec;
if (!verity_fec_is_enabled(v))
goto out;
mempool_destroy(f->rs_pool);
mempool_destroy(f->prealloc_pool);
mempool_destroy(f->extra_pool);
kmem_cache_destroy(f->cache);
if (f->data_bufio)
dm_bufio_client_destroy(f->data_bufio);
if (f->bufio)
dm_bufio_client_destroy(f->bufio);
if (f->dev)
dm_put_device(v->ti, f->dev);
out:
kfree(f);
v->fec = NULL;
}
static void *fec_rs_alloc(gfp_t gfp_mask, void *pool_data)
{
struct dm_verity *v = (struct dm_verity *)pool_data;
return init_rs(8, 0x11d, 0, 1, v->fec->roots);
}
static void fec_rs_free(void *element, void *pool_data)
{
struct rs_control *rs = (struct rs_control *)element;
if (rs)
free_rs(rs);
}
bool verity_is_fec_opt_arg(const char *arg_name)
{
return (!strcasecmp(arg_name, DM_VERITY_OPT_FEC_DEV) ||
!strcasecmp(arg_name, DM_VERITY_OPT_FEC_BLOCKS) ||
!strcasecmp(arg_name, DM_VERITY_OPT_FEC_START) ||
!strcasecmp(arg_name, DM_VERITY_OPT_FEC_ROOTS));
}
int verity_fec_parse_opt_args(struct dm_arg_set *as, struct dm_verity *v,
unsigned *argc, const char *arg_name)
{
int r;
struct dm_target *ti = v->ti;
const char *arg_value;
unsigned long long num_ll;
unsigned char num_c;
char dummy;
if (!*argc) {
ti->error = "FEC feature arguments require a value";
return -EINVAL;
}
arg_value = dm_shift_arg(as);
(*argc)--;
if (!strcasecmp(arg_name, DM_VERITY_OPT_FEC_DEV)) {
r = dm_get_device(ti, arg_value, FMODE_READ, &v->fec->dev);
if (r) {
ti->error = "FEC device lookup failed";
return r;
}
} else if (!strcasecmp(arg_name, DM_VERITY_OPT_FEC_BLOCKS)) {
if (sscanf(arg_value, "%llu%c", &num_ll, &dummy) != 1 ||
((sector_t)(num_ll << (v->data_dev_block_bits - SECTOR_SHIFT))
>> (v->data_dev_block_bits - SECTOR_SHIFT) != num_ll)) {
ti->error = "Invalid " DM_VERITY_OPT_FEC_BLOCKS;
return -EINVAL;
}
v->fec->blocks = num_ll;
} else if (!strcasecmp(arg_name, DM_VERITY_OPT_FEC_START)) {
if (sscanf(arg_value, "%llu%c", &num_ll, &dummy) != 1 ||
((sector_t)(num_ll << (v->data_dev_block_bits - SECTOR_SHIFT)) >>
(v->data_dev_block_bits - SECTOR_SHIFT) != num_ll)) {
ti->error = "Invalid " DM_VERITY_OPT_FEC_START;
return -EINVAL;
}
v->fec->start = num_ll;
} else if (!strcasecmp(arg_name, DM_VERITY_OPT_FEC_ROOTS)) {
if (sscanf(arg_value, "%hhu%c", &num_c, &dummy) != 1 || !num_c ||
num_c < (DM_VERITY_FEC_RSM - DM_VERITY_FEC_MAX_RSN) ||
num_c > (DM_VERITY_FEC_RSM - DM_VERITY_FEC_MIN_RSN)) {
ti->error = "Invalid " DM_VERITY_OPT_FEC_ROOTS;
return -EINVAL;
}
v->fec->roots = num_c;
} else {
ti->error = "Unrecognized verity FEC feature request";
return -EINVAL;
}
return 0;
}
/*
* Allocate dm_verity_fec for v->fec. Must be called before verity_fec_ctr.
*/
int verity_fec_ctr_alloc(struct dm_verity *v)
{
struct dm_verity_fec *f;
f = kzalloc(sizeof(struct dm_verity_fec), GFP_KERNEL);
if (!f) {
v->ti->error = "Cannot allocate FEC structure";
return -ENOMEM;
}
v->fec = f;
return 0;
}
/*
* Validate arguments and preallocate memory. Must be called after arguments
* have been parsed using verity_fec_parse_opt_args.
*/
int verity_fec_ctr(struct dm_verity *v)
{
struct dm_verity_fec *f = v->fec;
struct dm_target *ti = v->ti;
u64 hash_blocks;
if (!verity_fec_is_enabled(v)) {
verity_fec_dtr(v);
return 0;
}
/*
* FEC is computed over data blocks, possible metadata, and
* hash blocks. In other words, FEC covers total of fec_blocks
* blocks consisting of the following:
*
* data blocks | hash blocks | metadata (optional)
*
* We allow metadata after hash blocks to support a use case
* where all data is stored on the same device and FEC covers
* the entire area.
*
* If metadata is included, we require it to be available on the
* hash device after the hash blocks.
*/
hash_blocks = v->hash_blocks - v->hash_start;
/*
* Require matching block sizes for data and hash devices for
* simplicity.
*/
if (v->data_dev_block_bits != v->hash_dev_block_bits) {
ti->error = "Block sizes must match to use FEC";
return -EINVAL;
}
if (!f->roots) {
ti->error = "Missing " DM_VERITY_OPT_FEC_ROOTS;
return -EINVAL;
}
f->rsn = DM_VERITY_FEC_RSM - f->roots;
if (!f->blocks) {
ti->error = "Missing " DM_VERITY_OPT_FEC_BLOCKS;
return -EINVAL;
}
f->rounds = f->blocks;
if (sector_div(f->rounds, f->rsn))
f->rounds++;
/*
* Due to optional metadata, f->blocks can be larger than
* data_blocks and hash_blocks combined.
*/
if (f->blocks < v->data_blocks + hash_blocks || !f->rounds) {
ti->error = "Invalid " DM_VERITY_OPT_FEC_BLOCKS;
return -EINVAL;
}
/*
* Metadata is accessed through the hash device, so we require
* it to be large enough.
*/
f->hash_blocks = f->blocks - v->data_blocks;
if (dm_bufio_get_device_size(v->bufio) < f->hash_blocks) {
ti->error = "Hash device is too small for "
DM_VERITY_OPT_FEC_BLOCKS;
return -E2BIG;
}
f->bufio = dm_bufio_client_create(f->dev->bdev,
1 << v->data_dev_block_bits,
1, 0, NULL, NULL);
if (IS_ERR(f->bufio)) {
ti->error = "Cannot initialize FEC bufio client";
return PTR_ERR(f->bufio);
}
if (dm_bufio_get_device_size(f->bufio) <
((f->start + f->rounds * f->roots) >> v->data_dev_block_bits)) {
ti->error = "FEC device is too small";
return -E2BIG;
}
f->data_bufio = dm_bufio_client_create(v->data_dev->bdev,
1 << v->data_dev_block_bits,
1, 0, NULL, NULL);
if (IS_ERR(f->data_bufio)) {
ti->error = "Cannot initialize FEC data bufio client";
return PTR_ERR(f->data_bufio);
}
if (dm_bufio_get_device_size(f->data_bufio) < v->data_blocks) {
ti->error = "Data device is too small";
return -E2BIG;
}
/* Preallocate an rs_control structure for each worker thread */
f->rs_pool = mempool_create(num_online_cpus(), fec_rs_alloc,
fec_rs_free, (void *) v);
if (!f->rs_pool) {
ti->error = "Cannot allocate RS pool";
return -ENOMEM;
}
f->cache = kmem_cache_create("dm_verity_fec_buffers",
f->rsn << DM_VERITY_FEC_BUF_RS_BITS,
0, 0, NULL);
if (!f->cache) {
ti->error = "Cannot create FEC buffer cache";
return -ENOMEM;
}
/* Preallocate DM_VERITY_FEC_BUF_PREALLOC buffers for each thread */
f->prealloc_pool = mempool_create_slab_pool(num_online_cpus() *
DM_VERITY_FEC_BUF_PREALLOC,
f->cache);
if (!f->prealloc_pool) {
ti->error = "Cannot allocate FEC buffer prealloc pool";
return -ENOMEM;
}
f->extra_pool = mempool_create_slab_pool(0, f->cache);
if (!f->extra_pool) {
ti->error = "Cannot allocate FEC buffer extra pool";
return -ENOMEM;
}
/* Preallocate an output buffer for each thread */
f->output_pool = mempool_create_kmalloc_pool(num_online_cpus(),
1 << v->data_dev_block_bits);
if (!f->output_pool) {
ti->error = "Cannot allocate FEC output pool";
return -ENOMEM;
}
/* Reserve space for our per-bio data */
ti->per_io_data_size += sizeof(struct dm_verity_fec_io);
return 0;
}