[PATCH v2 36/51] netfs: Support encryption on Unbuffered/DIO write

From: David Howells
Date: Fri Nov 17 2023 - 16:22:19 EST

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Support unbuffered and direct I/O writes to an encrypted file. This may
require making an RMW cycle if the write is not appropriately aligned with
respect to the crypto blocks.

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Jeff Layton <jlayton@xxxxxxxxxx>
cc: linux-cachefs@xxxxxxxxxx
cc: linux-fsdevel@xxxxxxxxxxxxxxx
cc: linux-mm@xxxxxxxxx
---
fs/netfs/direct_read.c | 2 +-
fs/netfs/direct_write.c | 210 ++++++++++++++++++++++++++++++++++-
fs/netfs/internal.h | 8 ++
fs/netfs/io.c | 117 +++++++++++++++++++
fs/netfs/main.c | 1 +
include/linux/netfs.h | 4 +
include/trace/events/netfs.h | 1 +
7 files changed, 337 insertions(+), 6 deletions(-)

diff --git a/fs/netfs/direct_read.c b/fs/netfs/direct_read.c
index 158719b56900..c01cbe42db8a 100644
--- a/fs/netfs/direct_read.c
+++ b/fs/netfs/direct_read.c
@@ -88,7 +88,7 @@ static int netfs_copy_xarray_to_iter(struct netfs_io_request *rreq,
* If we did a direct read to a bounce buffer (say we needed to decrypt it),
* copy the data obtained to the destination iterator.
*/
-static int netfs_dio_copy_bounce_to_dest(struct netfs_io_request *rreq)
+int netfs_dio_copy_bounce_to_dest(struct netfs_io_request *rreq)
{
struct iov_iter *dest_iter = &rreq->iter;
struct kiocb *iocb = rreq->iocb;
diff --git a/fs/netfs/direct_write.c b/fs/netfs/direct_write.c
index b1a4921ac4a2..f9dea801d6dd 100644
--- a/fs/netfs/direct_write.c
+++ b/fs/netfs/direct_write.c
@@ -23,6 +23,100 @@ static void netfs_cleanup_dio_write(struct netfs_io_request *wreq)
}
}

+/*
+ * Allocate a bunch of pages and add them into the xarray buffer starting at
+ * the given index.
+ */
+static int netfs_alloc_buffer(struct xarray *xa, pgoff_t index, unsigned int nr_pages)
+{
+ struct page *page;
+ unsigned int n;
+ int ret = 0;
+ LIST_HEAD(list);
+
+ n = alloc_pages_bulk_list(GFP_NOIO, nr_pages, &list);
+ if (n < nr_pages) {
+ ret = -ENOMEM;
+ }
+
+ while ((page = list_first_entry_or_null(&list, struct page, lru))) {
+ list_del(&page->lru);
+ page->index = index;
+ ret = xa_insert(xa, index++, page, GFP_NOIO);
+ if (ret < 0)
+ break;
+ }
+
+ while ((page = list_first_entry_or_null(&list, struct page, lru))) {
+ list_del(&page->lru);
+ __free_page(page);
+ }
+ return ret;
+}
+
+/*
+ * Copy all of the data from the source iterator into folios in the destination
+ * xarray. We cannot step through and kmap the source iterator if it's an
+ * iovec, so we have to step through the xarray and drop the RCU lock each
+ * time.
+ */
+static int netfs_copy_iter_to_xarray(struct iov_iter *src, struct xarray *xa,
+ unsigned long long start)
+{
+ struct folio *folio;
+ void *base;
+ pgoff_t index = start / PAGE_SIZE;
+ size_t len, copied, count = iov_iter_count(src);
+
+ XA_STATE(xas, xa, index);
+
+ _enter("%zx", count);
+
+ if (!count)
+ return -EIO;
+
+ len = PAGE_SIZE - offset_in_page(start);
+ rcu_read_lock();
+ xas_for_each(&xas, folio, ULONG_MAX) {
+ size_t offset;
+
+ if (xas_retry(&xas, folio))
+ continue;
+
+ /* There shouldn't be a need to call xas_pause() as no one else
+ * can see the xarray we're iterating over.
+ */
+ rcu_read_unlock();
+
+ offset = offset_in_folio(folio, start);
+ _debug("folio %lx +%zx [%llx]", folio->index, offset, start);
+
+ while (offset < folio_size(folio)) {
+ len = min(count, len);
+
+ base = kmap_local_folio(folio, offset);
+ copied = copy_from_iter(base, len, src);
+ kunmap_local(base);
+ if (copied != len)
+ goto out;
+ count -= len;
+ if (count == 0)
+ goto out;
+
+ start += len;
+ offset += len;
+ len = PAGE_SIZE;
+ }
+
+ rcu_read_lock();
+ }
+
+ rcu_read_unlock();
+out:
+ _leave(" = %zx", count);
+ return count ? -EIO : 0;
+}
+
/*
* Perform an unbuffered write where we may have to do an RMW operation on an
* encrypted file. This can also be used for direct I/O writes.
@@ -31,20 +125,47 @@ ssize_t netfs_unbuffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *
struct netfs_group *netfs_group)
{
struct netfs_io_request *wreq;
+ struct netfs_inode *ctx = netfs_inode(file_inode(iocb->ki_filp));
+ unsigned long long real_size = ctx->remote_i_size;
unsigned long long start = iocb->ki_pos;
unsigned long long end = start + iov_iter_count(iter);
ssize_t ret, n;
- bool async = !is_sync_kiocb(iocb);
+ size_t min_bsize = 1UL << ctx->min_bshift;
+ size_t bmask = min_bsize - 1;
+ size_t gap_before = start & bmask;
+ size_t gap_after = (min_bsize - end) & bmask;
+ bool use_bounce, async = !is_sync_kiocb(iocb);
+ enum {
+ DIRECT_IO, COPY_TO_BOUNCE, ENC_TO_BOUNCE, COPY_THEN_ENC,
+ } buffering;

_enter("");

+ /* The real size must be rounded out to the crypto block size plus
+ * any trailer we might want to attach.
+ */
+ if (real_size && ctx->crypto_bshift) {
+ size_t cmask = 1UL << ctx->crypto_bshift;
+
+ if (real_size < ctx->crypto_trailer)
+ return -EIO;
+ if ((real_size - ctx->crypto_trailer) & cmask)
+ return -EIO;
+ real_size -= ctx->crypto_trailer;
+ }
+
/* We're going to need a bounce buffer if what we transmit is going to
* be different in some way to the source buffer, e.g. because it gets
* encrypted/compressed or because it needs expanding to a block size.
*/
- // TODO
+ use_bounce = test_bit(NETFS_ICTX_ENCRYPTED, &ctx->flags);
+ if (gap_before || gap_after) {
+ if (iocb->ki_flags & IOCB_DIRECT)
+ return -EINVAL;
+ use_bounce = true;
+ }

- _debug("uw %llx-%llx", start, end);
+ _debug("uw %llx-%llx +%zx,%zx", start, end, gap_before, gap_after);

wreq = netfs_alloc_request(iocb->ki_filp->f_mapping, iocb->ki_filp,
start, end - start,
@@ -53,7 +174,57 @@ ssize_t netfs_unbuffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *
if (IS_ERR(wreq))
return PTR_ERR(wreq);

- {
+ if (use_bounce) {
+ unsigned long long bstart = start - gap_before;
+ unsigned long long bend = end + gap_after;
+ pgoff_t first = bstart / PAGE_SIZE;
+ pgoff_t last = (bend - 1) / PAGE_SIZE;
+
+ _debug("bounce %llx-%llx %lx-%lx", bstart, bend, first, last);
+
+ ret = netfs_alloc_buffer(&wreq->bounce, first, last - first + 1);
+ if (ret < 0)
+ goto out;
+
+ iov_iter_xarray(&wreq->io_iter, READ, &wreq->bounce,
+ bstart, bend - bstart);
+
+ if (gap_before || gap_after)
+ async = false; /* We may have to repeat the RMW cycle */
+ }
+
+repeat_rmw_cycle:
+ if (use_bounce) {
+ /* If we're going to need to do an RMW cycle, fill in the gaps
+ * at the ends of the buffer.
+ */
+ if (gap_before || gap_after) {
+ struct iov_iter buffer = wreq->io_iter;
+
+ if ((gap_before && start - gap_before < real_size) ||
+ (gap_after && end < real_size)) {
+ ret = netfs_rmw_read(wreq, iocb->ki_filp,
+ start - gap_before, gap_before,
+ end, end < real_size ? gap_after : 0);
+ if (ret < 0)
+ goto out;
+ }
+
+ if (gap_before && start - gap_before >= real_size)
+ iov_iter_zero(gap_before, &buffer);
+ if (gap_after && end >= real_size) {
+ iov_iter_advance(&buffer, end - start);
+ iov_iter_zero(gap_after, &buffer);
+ }
+ }
+
+ if (!test_bit(NETFS_RREQ_CONTENT_ENCRYPTION, &wreq->flags))
+ buffering = COPY_TO_BOUNCE;
+ else if (!gap_before && !gap_after && netfs_is_crypto_aligned(wreq, iter))
+ buffering = ENC_TO_BOUNCE;
+ else
+ buffering = COPY_THEN_ENC;
+ } else {
/* If this is an async op and we're not using a bounce buffer,
* we have to save the source buffer as the iterator is only
* good until we return. In such a case, extract an iterator
@@ -77,10 +248,25 @@ ssize_t netfs_unbuffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *
}

wreq->io_iter = wreq->iter;
+ buffering = DIRECT_IO;
}

/* Copy the data into the bounce buffer and encrypt it. */
- // TODO
+ if (buffering == COPY_TO_BOUNCE ||
+ buffering == COPY_THEN_ENC) {
+ ret = netfs_copy_iter_to_xarray(iter, &wreq->bounce, wreq->start);
+ if (ret < 0)
+ goto out;
+ wreq->iter = wreq->io_iter;
+ wreq->start -= gap_before;
+ wreq->len += gap_before + gap_after;
+ }
+
+ if (buffering == COPY_THEN_ENC ||
+ buffering == ENC_TO_BOUNCE) {
+ if (!netfs_encrypt(wreq))
+ goto out;
+ }

/* Dispatch the write. */
__set_bit(NETFS_RREQ_UPLOAD_TO_SERVER, &wreq->flags);
@@ -101,6 +287,20 @@ ssize_t netfs_unbuffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *
wait_on_bit(&wreq->flags, NETFS_RREQ_IN_PROGRESS,
TASK_UNINTERRUPTIBLE);

+ /* See if the write failed due to a 3rd party race when doing
+ * an RMW on a partially modified block in an encrypted file.
+ */
+ if (test_and_clear_bit(NETFS_RREQ_REPEAT_RMW, &wreq->flags)) {
+ netfs_clear_subrequests(wreq, false);
+ iov_iter_revert(iter, end - start);
+ wreq->error = 0;
+ wreq->start = start;
+ wreq->len = end - start;
+ wreq->transferred = 0;
+ wreq->submitted = 0;
+ goto repeat_rmw_cycle;
+ }
+
ret = wreq->error;
_debug("waited = %zd", ret);
if (ret == 0) {
diff --git a/fs/netfs/internal.h b/fs/netfs/internal.h
index 447a67301329..782b73b1f5a7 100644
--- a/fs/netfs/internal.h
+++ b/fs/netfs/internal.h
@@ -28,6 +28,11 @@ int netfs_prefetch_for_write(struct file *file, struct folio *folio,
bool netfs_encrypt(struct netfs_io_request *wreq);
void netfs_decrypt(struct netfs_io_request *rreq);

+/*
+ * direct_read.c
+ */
+int netfs_dio_copy_bounce_to_dest(struct netfs_io_request *rreq);
+
/*
* direct_write.c
*/
@@ -38,6 +43,9 @@ ssize_t netfs_unbuffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *
* io.c
*/
int netfs_begin_read(struct netfs_io_request *rreq, bool sync);
+ssize_t netfs_rmw_read(struct netfs_io_request *wreq, struct file *file,
+ unsigned long long start1, size_t len1,
+ unsigned long long start2, size_t len2);

/*
* main.c
diff --git a/fs/netfs/io.c b/fs/netfs/io.c
index 9887b22e4cb3..14a9f3312d3b 100644
--- a/fs/netfs/io.c
+++ b/fs/netfs/io.c
@@ -775,3 +775,120 @@ int netfs_begin_read(struct netfs_io_request *rreq, bool sync)
out:
return ret;
}
+
+static bool netfs_rmw_read_one(struct netfs_io_request *rreq,
+ unsigned long long start, size_t len)
+{
+ struct netfs_inode *ctx = netfs_inode(rreq->inode);
+ struct iov_iter io_iter;
+ unsigned long long pstart, end = start + len;
+ pgoff_t first, last;
+ ssize_t ret;
+ size_t min_bsize = 1UL << ctx->min_bshift;
+
+ /* Determine the block we need to load. */
+ end = round_up(end, min_bsize);
+ start = round_down(start, min_bsize);
+
+ /* Determine the folios we need to insert. */
+ pstart = round_down(start, PAGE_SIZE);
+ first = pstart / PAGE_SIZE;
+ last = DIV_ROUND_UP(end, PAGE_SIZE);
+
+ ret = netfs_add_folios_to_buffer(&rreq->bounce, rreq->mapping,
+ first, last, GFP_NOFS);
+ if (ret < 0) {
+ rreq->error = ret;
+ return false;
+ }
+
+ rreq->start = start;
+ rreq->len = len;
+ rreq->submitted = 0;
+ iov_iter_xarray(&rreq->io_iter, ITER_DEST, &rreq->bounce, start, len);
+
+ io_iter = rreq->io_iter;
+ do {
+ _debug("submit %llx + %zx >= %llx",
+ rreq->start, rreq->submitted, rreq->i_size);
+ if (rreq->start + rreq->submitted >= rreq->i_size)
+ break;
+ if (!netfs_rreq_submit_slice(rreq, &io_iter, &rreq->subreq_counter))
+ break;
+ } while (rreq->submitted < rreq->len);
+
+ if (rreq->submitted < rreq->len) {
+ netfs_put_request(rreq, false, netfs_rreq_trace_put_no_submit);
+ return false;
+ }
+
+ return true;
+}
+
+/*
+ * Begin the process of reading in one or two chunks of data for use by
+ * unbuffered write to perform an RMW cycle. We don't read directly into the
+ * write buffer as this may get called to redo the read in the case that a
+ * conditional write fails due to conflicting 3rd-party modifications.
+ */
+ssize_t netfs_rmw_read(struct netfs_io_request *wreq, struct file *file,
+ unsigned long long start1, size_t len1,
+ unsigned long long start2, size_t len2)
+{
+ struct netfs_io_request *rreq;
+ ssize_t ret;
+
+ _enter("RMW:R=%x %llx-%llx %llx-%llx",
+ rreq->debug_id, start1, start1 + len1 - 1, start2, start2 + len2 - 1);
+
+ rreq = netfs_alloc_request(wreq->mapping, file,
+ start1, start2 - start1 + len2, NETFS_RMW_READ);
+ if (IS_ERR(rreq))
+ return PTR_ERR(rreq);
+
+ INIT_WORK(&rreq->work, netfs_rreq_work);
+
+ rreq->iter = wreq->io_iter;
+ __set_bit(NETFS_RREQ_CRYPT_IN_PLACE, &rreq->flags);
+ __set_bit(NETFS_RREQ_USE_BOUNCE_BUFFER, &rreq->flags);
+
+ /* Chop the reads into slices according to what the netfs wants and
+ * submit each one.
+ */
+ netfs_get_request(rreq, netfs_rreq_trace_get_for_outstanding);
+ atomic_set(&rreq->nr_outstanding, 1);
+ if (len1 && !netfs_rmw_read_one(rreq, start1, len1))
+ goto wait;
+ if (len2)
+ netfs_rmw_read_one(rreq, start2, len2);
+
+wait:
+ /* Keep nr_outstanding incremented so that the ref always belongs to us
+ * and the service code isn't punted off to a random thread pool to
+ * process.
+ */
+ for (;;) {
+ wait_var_event(&rreq->nr_outstanding,
+ atomic_read(&rreq->nr_outstanding) == 1);
+ netfs_rreq_assess(rreq, false);
+ if (atomic_read(&rreq->nr_outstanding) == 1)
+ break;
+ cond_resched();
+ }
+
+ trace_netfs_rreq(wreq, netfs_rreq_trace_wait_ip);
+ wait_on_bit(&wreq->flags, NETFS_RREQ_IN_PROGRESS,
+ TASK_UNINTERRUPTIBLE);
+
+ ret = rreq->error;
+ if (ret == 0 && rreq->submitted < rreq->len) {
+ trace_netfs_failure(rreq, NULL, ret, netfs_fail_short_read);
+ ret = -EIO;
+ }
+
+ if (ret == 0)
+ ret = netfs_dio_copy_bounce_to_dest(rreq);
+
+ netfs_put_request(rreq, false, netfs_rreq_trace_put_return);
+ return ret;
+}
diff --git a/fs/netfs/main.c b/fs/netfs/main.c
index 1cf10f9c4c1f..b335e6a50f9c 100644
--- a/fs/netfs/main.c
+++ b/fs/netfs/main.c
@@ -33,6 +33,7 @@ static const char *netfs_origins[nr__netfs_io_origin] = {
[NETFS_READPAGE] = "RP",
[NETFS_READ_FOR_WRITE] = "RW",
[NETFS_WRITEBACK] = "WB",
+ [NETFS_RMW_READ] = "RM",
[NETFS_UNBUFFERED_WRITE] = "UW",
[NETFS_DIO_READ] = "DR",
[NETFS_DIO_WRITE] = "DW",
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index 364361cc93be..c3d1eac1ce51 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -145,6 +145,7 @@ struct netfs_inode {
#define NETFS_ICTX_ENCRYPTED 2 /* The file contents are encrypted */
unsigned char min_bshift; /* log2 min block size for bounding box or 0 */
unsigned char crypto_bshift; /* log2 of crypto block size */
+ unsigned char crypto_trailer; /* Size of crypto trailer */
};

/*
@@ -233,6 +234,7 @@ enum netfs_io_origin {
NETFS_READPAGE, /* This read is a synchronous read */
NETFS_READ_FOR_WRITE, /* This read is to prepare a write */
NETFS_WRITEBACK, /* This write was triggered by writepages */
+ NETFS_RMW_READ, /* This is an unbuffered read for RMW */
NETFS_UNBUFFERED_WRITE, /* This is an unbuffered write */
NETFS_DIO_READ, /* This is a direct I/O read */
NETFS_DIO_WRITE, /* This is a direct I/O write */
@@ -291,6 +293,7 @@ struct netfs_io_request {
#define NETFS_RREQ_BLOCKED 10 /* We blocked */
#define NETFS_RREQ_CONTENT_ENCRYPTION 11 /* Content encryption is in use */
#define NETFS_RREQ_CRYPT_IN_PLACE 12 /* Enc/dec in place in ->io_iter */
+#define NETFS_RREQ_REPEAT_RMW 13 /* Need to repeat RMW cycle */
const struct netfs_request_ops *netfs_ops;
void (*cleanup)(struct netfs_io_request *req);
};
@@ -479,6 +482,7 @@ static inline void netfs_inode_init(struct netfs_inode *ctx,
ctx->flags = 0;
ctx->min_bshift = 0;
ctx->crypto_bshift = 0;
+ ctx->crypto_trailer = 0;
#if IS_ENABLED(CONFIG_FSCACHE)
ctx->cache = NULL;
#endif
diff --git a/include/trace/events/netfs.h b/include/trace/events/netfs.h
index 2f35057602fa..825946f510ee 100644
--- a/include/trace/events/netfs.h
+++ b/include/trace/events/netfs.h
@@ -33,6 +33,7 @@
EM(NETFS_READPAGE, "RP") \
EM(NETFS_READ_FOR_WRITE, "RW") \
EM(NETFS_WRITEBACK, "WB") \
+ EM(NETFS_RMW_READ, "RM") \
EM(NETFS_UNBUFFERED_WRITE, "UW") \
EM(NETFS_DIO_READ, "DR") \
E_(NETFS_DIO_WRITE, "DW")

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