null_blk: Zero-initialize read buffers in non-memory-backed mode
This patch suppresses an uninteresting KMSAN complaint without affecting
performance of the null_blk driver if CONFIG_KMSAN is disabled.
Reported-by: Alexander Potapenko <glider@google.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Tested-by: Alexander Potapenko <glider@google.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Damien Le Moal <damien.lemoal@wdc.com>
Cc: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Cc: Alexander Potapenko <glider@google.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/drivers/block/null_blk_main.c b/drivers/block/null_blk_main.c
index 8efd877..4f37b9f 100644
--- a/drivers/block/null_blk_main.c
+++ b/drivers/block/null_blk_main.c
@@ -1250,8 +1250,34 @@ static inline blk_status_t null_handle_memory_backed(struct nullb_cmd *cmd,
return errno_to_blk_status(err);
}
+static void nullb_zero_read_cmd_buffer(struct nullb_cmd *cmd)
+{
+ struct nullb_device *dev = cmd->nq->dev;
+ struct bio *bio;
+
+ if (dev->memory_backed)
+ return;
+
+ if (dev->queue_mode == NULL_Q_BIO && bio_op(cmd->bio) == REQ_OP_READ) {
+ zero_fill_bio(cmd->bio);
+ } else if (req_op(cmd->rq) == REQ_OP_READ) {
+ __rq_for_each_bio(bio, cmd->rq)
+ zero_fill_bio(bio);
+ }
+}
+
static inline void nullb_complete_cmd(struct nullb_cmd *cmd)
{
+ /*
+ * Since root privileges are required to configure the null_blk
+ * driver, it is fine that this driver does not initialize the
+ * data buffers of read commands. Zero-initialize these buffers
+ * anyway if KMSAN is enabled to prevent that KMSAN complains
+ * about null_blk not initializing read data buffers.
+ */
+ if (IS_ENABLED(CONFIG_KMSAN))
+ nullb_zero_read_cmd_buffer(cmd);
+
/* Complete IO by inline, softirq or timer */
switch (cmd->nq->dev->irqmode) {
case NULL_IRQ_SOFTIRQ:
