bhyve nvme: Fix out-of-bound IOV array access

Summary:
NVMe operations indicate the memory region(s) associated with a command
via physical region pages (PRPs). Since each PRP has a fixed size,
contiguous memory regions larger than the PRP size require multiple PRP
entries.

Instead of issuing a blockif call for each PRP, the NVMe emulation
concatenates multiple contiguous PRP entries into a single blockif
request. The test for contiguous regions has a bug such that it
mistakenly treats an initial PRP address of zero as a contiguous range
and concatenates it with the previous. But because there is no previous
IOV, the concatenation code corrupts the IO request structure and leads
to a segmentation fault when the blockif request completes.

Fix is to test for the existence of a previous range before trying to
concatenate the current range with the previous one.

While in the area, rename pci_nvme_append_iov_req()'s lba parameter to
offset to match its usage.

PR:             264177
Reported by:    Robert Morris <rtm@lcs.mit.edu>
Reviewed by:	jhb
MFC after:      2 weeks
Differential Revision:	https://reviews.freebsd.org/D35328

1 files changed, 14 insertions, 4 deletions

diff --git a/usr.sbin/bhyve/pci_nvme.c b/usr.sbin/bhyve/pci_nvme.c
index 098f0aba1084..5f54e4107c10 100644
--- a/usr.sbin/bhyve/pci_nvme.c
+++ b/usr.sbin/bhyve/pci_nvme.c
@@ -2168,9 +2168,10 @@ pci_nvme_out_of_range(struct pci_nvme_blockstore *nvstore, uint64_t slba,
 
 static int
 pci_nvme_append_iov_req(struct pci_nvme_softc *sc, struct pci_nvme_ioreq *req,
-	uint64_t gpaddr, size_t size, int do_write, uint64_t lba)
+	uint64_t gpaddr, size_t size, int do_write, uint64_t offset)
 {
 	int iovidx;
+	bool range_is_contiguous;
 
 	if (req == NULL)
 		return (-1);
@@ -2179,8 +2180,17 @@ pci_nvme_append_iov_req(struct pci_nvme_softc *sc, struct pci_nvme_ioreq *req,
 		return (-1);
 	}
 
-	/* concatenate contig block-iovs to minimize number of iovs */
-	if ((req->prev_gpaddr + req->prev_size) == gpaddr) {
+	/*
+	 * Minimize the number of IOVs by concatenating contiguous address
+	 * ranges. If the IOV count is zero, there is no previous range to
+	 * concatenate.
+	 */
+	if (req->io_req.br_iovcnt == 0)
+		range_is_contiguous = false;
+	else
+		range_is_contiguous = (req->prev_gpaddr + req->prev_size) == gpaddr;
+
+	if (range_is_contiguous) {
 		iovidx = req->io_req.br_iovcnt - 1;
 
 		req->io_req.br_iov[iovidx].iov_base =
@@ -2194,7 +2204,7 @@ pci_nvme_append_iov_req(struct pci_nvme_softc *sc, struct pci_nvme_ioreq *req,
 	} else {
 		iovidx = req->io_req.br_iovcnt;
 		if (iovidx == 0) {
-			req->io_req.br_offset = lba;
+			req->io_req.br_offset = offset;
 			req->io_req.br_resid = 0;
 			req->io_req.br_param = req;
 		}