RDMA/cxgb4: Add missing padding at end of struct c4iw_create_cq_resp

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: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/infiniband/hw/cxgb4/cq.c b/drivers/infiniband/hw/cxgb4/cq.c
index da9364e..3bd6b69 100644 (file)
--- a/drivers/infiniband/hw/cxgb4/cq.c
+++ b/drivers/infiniband/hw/cxgb4/cq.c
@@ -833,7 +833,6 @@ struct ib_cq *c4iw_create_cq(struct ib_device *ibdev, int entries,
                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;
@@ -844,7 +843,8 @@ struct ib_cq *c4iw_create_cq(struct ib_device *ibdev, int entries,
                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;
 

diff --git a/drivers/infiniband/hw/cxgb4/user.h b/drivers/infiniband/hw/cxgb4/user.h
index e6669d5..06e8938 100644 (file)
--- 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) */
 };