[PATCH 3.12 026/170] IB/mlx5: add missing padding at end of struct mlx5_ib_create_cq

Jiri Slaby
2014-07-18T13:09:16Z

From: Yann Droneaud <ydroneaud@opteya.com>

3.12-stable review patch. If anyone has any objections, please let me know.

===============

commit a8237b32a3faab155a5dc8f886452147ce73da3e upstream.

The i386 ABI disagrees with most other ABIs regarding alignment of
data type larger than 4 bytes: on most ABIs a padding must be added at
end of the structures, while it is not required on i386.

So for most ABI struct mlx5_ib_create_cq get padded to be aligned on a
8 bytes multiple, while for i386, such padding is not added.

The tool pahole can be used to find such implicit padding:

$ pahole --anon_include \
--nested_anon_include \
--recursive \
--class_name mlx5_ib_create_cq \
drivers/infiniband/hw/mlx5/mlx5_ib.o

Then, structure layout can be compared between i386 and x86_64:

# +++ obj-i386/drivers/infiniband/hw/mlx5/mlx5_ib.o.pahole.txt 2014-03-28 11:43:07.386413682 +0100
# --- obj-x86_64/drivers/infiniband/hw/mlx5/mlx5_ib.o.pahole.txt 2014-03-27 13:06:17.788472721 +0100
# @@ -34,9 +34,8 @@ struct mlx5_ib_create_cq {
# __u64 db_addr; /* 8 8 */
# __u32 cqe_size; /* 16 4 */
#
# - /* size: 20, cachelines: 1, members: 3 */
# - /* last cacheline: 20 bytes */
# + /* size: 24, cachelines: 1, members: 3 */
# + /* padding: 4 */
# + /* last cacheline: 24 bytes */
# };

This ABI disagreement will make an x86_64 kernel try to read past the
buffer provided by an i386 binary.

When boundary check will be implemented, a x86_64 kernel will refuse
to read past the i386 userspace provided buffer and the uverb will
fail.

Anyway, if the structure lies in memory on a page boundary and next
page is not mapped, ib_copy_from_udata() will fail when trying to read
the 4 bytes of padding and the uverb will fail.

This patch makes create_cq_user() takes care of the input data size to
handle the case where no padding is provided.

This way, x86_64 kernel will be able to handle struct
mlx5_ib_create_cq as sent by unpatched and patched i386 libmlx5.

Link: http://marc.info/?i=cover.1399309513.git.ydroneaud@opteya.com
Fixes: e126ba97dba9e ("mlx5: Add driver for Mellanox Connect-IB adapter")
Signed-off-by: Yann Droneaud <ydroneaud@opteya.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
drivers/infiniband/hw/mlx5/cq.c | 13 ++++++++++++-
drivers/infiniband/hw/mlx5/user.h | 1 +
2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/infiniband/hw/mlx5/cq.c b/drivers/infiniband/hw/mlx5/cq.c
index 344ab03948a3..706833ab7e7e 100644
--- a/drivers/infiniband/hw/mlx5/cq.c
+++ b/drivers/infiniband/hw/mlx5/cq.c
@@ -32,6 +32,7 @@

#include <linux/kref.h>
#include <rdma/ib_umem.h>
+#include <rdma/ib_user_verbs.h>
#include "mlx5_ib.h"
#include "user.h"

@@ -518,14 +519,24 @@ static int create_cq_user(struct mlx5_ib_dev *dev, struct ib_udata *udata,
int *cqe_size, int *index, int *inlen)
{
struct mlx5_ib_create_cq ucmd;
+ size_t ucmdlen;
int page_shift;
int npages;
int ncont;
int err;

- if (ib_copy_from_udata(&ucmd, udata, sizeof(ucmd)))
+ ucmdlen =
+ (udata->inlen - sizeof(struct ib_uverbs_cmd_hdr) <
+ sizeof(ucmd)) ? (sizeof(ucmd) -
+ sizeof(ucmd.reserved)) : sizeof(ucmd);
+
+ if (ib_copy_from_udata(&ucmd, udata, ucmdlen))
return -EFAULT;

+ if (ucmdlen == sizeof(ucmd) &&
+ ucmd.reserved != 0)
+ return -EINVAL;
+
if (ucmd.cqe_size != 64 && ucmd.cqe_size != 128)
return -EINVAL;

diff --git a/drivers/infiniband/hw/mlx5/user.h b/drivers/infiniband/hw/mlx5/user.h
index a886de3e593c..e7da977e2548 100644
--- a/drivers/infiniband/hw/mlx5/user.h
+++ b/drivers/infiniband/hw/mlx5/user.h
@@ -84,6 +84,7 @@ struct mlx5_ib_create_cq {
__u64 buf_addr;
__u64 db_addr;
__u32 cqe_size;
+ __u32 reserved; /* explicit padding (optional on i386) */
};

struct mlx5_ib_create_cq_resp {
--
2.0.0