[PATCH 3.15 20/66] RDMA/cxgb4: Add missing padding at end of struct c4iw_create_cq_resp

Greg Kroah-Hartman
2014-07-04T22:16:38Z

From: Yann Droneaud <ydroneaud@opteya.com>

commit b6f04d3d21458818073a2f5af5339f958864bf71 upstream.

The i386 ABI disagrees with most other ABIs regarding alignment of
data types 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 c4iw_create_cq_resp gets implicitly 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 c4iw_create_cq_resp \
drivers/infiniband/hw/cxgb4/iw_cxgb4.o

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

# +++ obj-i386/drivers/infiniband/hw/cxgb4/iw_cxgb4.o.pahole.txt 2014-03-28 11:43:05.547432195 +0100
# --- obj-x86_64/drivers/infiniband/hw/cxgb4/iw_cxgb4.o.pahole.txt 2014-03-28 10:55:10.990133017 +0100
# @@ -14,9 +13,8 @@ struct c4iw_create_cq_resp {
# __u32 size; /* 28 4 */
# __u32 qid_mask; /* 32 4 */
#
# - /* size: 36, cachelines: 1, members: 6 */
# - /* last cacheline: 36 bytes */
# + /* size: 40, cachelines: 1, members: 6 */
# + /* padding: 4 */
# + /* last cacheline: 40 bytes */
# };

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

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

If the structure is on a page boundary and the next page is not
mapped, ib_copy_to_udata() will fail and the uverb will fail.

This patch adds an explicit padding at end of structure
c4iw_create_cq_resp, and, like 92b0ca7cb149 ("IB/mlx5: Fix stack info
leak in mlx5_ib_alloc_ucontext()"), makes function c4iw_create_cq()
not writting this padding field to userspace. This way, x86_64 kernel
will be able to write struct c4iw_create_cq_resp as expected by
unpatched and patched i386 libcxgb4.

Link: http://marc.info/?i=cover.1399309513.git.ydroneaud@opteya.com
Fixes: cfdda9d764362 ("RDMA/cxgb4: Add driver for Chelsio T4 RNIC")
Fixes: e24a72a3302a6 ("RDMA/cxgb4: Fix four byte info leak in c4iw_create_cq()")
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Yann Droneaud <ydroneaud@opteya.com>
Acked-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/infiniband/hw/cxgb4/cq.c | 4 ++--
drivers/infiniband/hw/cxgb4/user.h | 1 +
2 files changed, 3 insertions(+), 2 deletions(-)

--- a/drivers/infiniband/hw/cxgb4/cq.c
+++ b/drivers/infiniband/hw/cxgb4/cq.c
@@ -940,7 +940,6 @@ struct ib_cq *c4iw_create_cq(struct ib_d
if (!mm2)
goto err4;

- memset(&uresp, 0, sizeof(uresp));
uresp.qid_mask = rhp->rdev.cqmask;
uresp.cqid = chp->cq.cqid;
uresp.size = chp->cq.size;
@@ -951,7 +950,8 @@ struct ib_cq *c4iw_create_cq(struct ib_d
uresp.gts_key = ucontext->key;
ucontext->key += PAGE_SIZE;
spin_unlock(&ucontext->mmap_lock);
- ret = ib_copy_to_udata(udata, &uresp, sizeof uresp);
+ ret = ib_copy_to_udata(udata, &uresp,
+ sizeof(uresp) - sizeof(uresp.reserved));
if (ret)
goto err5;

--- a/drivers/infiniband/hw/cxgb4/user.h
+++ b/drivers/infiniband/hw/cxgb4/user.h
@@ -48,6 +48,7 @@ struct c4iw_create_cq_resp {
__u32 cqid;
__u32 size;
__u32 qid_mask;
+ __u32 reserved; /* explicit padding (optional for i386) */
};