/* * 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) { 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: dm_bufio_release(buf); 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_req(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) goto done; /* * 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, GFP_NOIO); fec_for_each_prealloc_buffer(n) { if (fio->bufs[n]) continue; fio->bufs[n] = mempool_alloc(&v->fec->prealloc_pool, GFP_NOWAIT); 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_NOWAIT); /* 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); 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_req(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 (fio->level >= DM_VERITY_FEC_MAX_RECURSION) { DMWARN_LIMIT("%s: FEC: recursion too deep", v->data_dev->name); return -EIO; } fio->level++; 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) goto done; } 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); } done: fio->level--; 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; fio->level = 0; } /* * 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_exit(&f->rs_pool); mempool_exit(&f->prealloc_pool); mempool_exit(&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_gfp(8, 0x11d, 0, 1, v->fec->roots, gfp_mask); } 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; int ret; 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 */ ret = mempool_init(&f->rs_pool, num_online_cpus(), fec_rs_alloc, fec_rs_free, (void *) v); if (ret) { ti->error = "Cannot allocate RS pool"; return ret; } 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 */ ret = mempool_init_slab_pool(&f->prealloc_pool, num_online_cpus() * DM_VERITY_FEC_BUF_PREALLOC, f->cache); if (ret) { ti->error = "Cannot allocate FEC buffer prealloc pool"; return ret; } ret = mempool_init_slab_pool(&f->extra_pool, 0, f->cache); if (ret) { ti->error = "Cannot allocate FEC buffer extra pool"; return ret; } /* Preallocate an output buffer for each thread */ ret = mempool_init_kmalloc_pool(&f->output_pool, num_online_cpus(), 1 << v->data_dev_block_bits); if (ret) { ti->error = "Cannot allocate FEC output pool"; return ret; } /* Reserve space for our per-bio data */ ti->per_io_data_size += sizeof(struct dm_verity_fec_io); return 0; }