[PATCH 5.13 096/113] net/rds: dma_map_sg is entitled to merge entries

From: Greg Kroah-Hartman
Date: Wed Sep 01 2021 - 08:55:12 EST

From: Gerd Rausch <gerd.rausch@xxxxxxxxxx>

[ Upstream commit fb4b1373dcab086d0619c29310f0466a0b2ceb8a ]

Function "dma_map_sg" is entitled to merge adjacent entries
and return a value smaller than what was passed as "nents".

Subsequently "ib_map_mr_sg" needs to work with this value ("sg_dma_len")
rather than the original "nents" parameter ("sg_len").

This old RDS bug was exposed and reliably causes kernel panics
(using RDMA operations "rds-stress -D") on x86_64 starting with:
commit c588072bba6b ("iommu/vt-d: Convert intel iommu driver to the iommu ops")

Simply put: Linux 5.11 and later.

Signed-off-by: Gerd Rausch <gerd.rausch@xxxxxxxxxx>
Acked-by: Santosh Shilimkar <santosh.shilimkar@xxxxxxxxxx>
Link: https://lore.kernel.org/r/60efc69f-1f35-529d-a7ef-da0549cad143@xxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
net/rds/ib_frmr.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/rds/ib_frmr.c b/net/rds/ib_frmr.c
index 9b6ffff72f2d..28c1b0022178 100644
--- a/net/rds/ib_frmr.c
+++ b/net/rds/ib_frmr.c
@@ -131,9 +131,9 @@ static int rds_ib_post_reg_frmr(struct rds_ib_mr *ibmr)

- ret = ib_map_mr_sg_zbva(frmr->mr, ibmr->sg, ibmr->sg_len,
+ ret = ib_map_mr_sg_zbva(frmr->mr, ibmr->sg, ibmr->sg_dma_len,
&off, PAGE_SIZE);
- if (unlikely(ret != ibmr->sg_len))
+ if (unlikely(ret != ibmr->sg_dma_len))
return ret < 0 ? ret : -EINVAL;

if (cmpxchg(&frmr->fr_state,