On Thu, Aug 19, 2021 at 01:47:57PM -0300, Jason Gunthorpe wrote:

On Thu, Aug 19, 2021 at 09:19:08AM -0700, Kees Cook wrote:

quoted

On Thu, Aug 19, 2021 at 09:27:16AM -0300, Jason Gunthorpe wrote:

quoted

On Tue, Aug 17, 2021 at 11:05:26PM -0700, Kees Cook wrote:

quoted

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memset(), avoid intentionally writing across
neighboring fields.

Add struct_group() to mark region of struct mlx5_ib_mr that should be
initialized to zero.

Cc: Leon Romanovsky <leon@kernel.org>
Cc: Doug Ledford <redacted>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: linux-rdma@vger.kernel.org
Signed-off-by: Kees Cook <redacted>
 drivers/infiniband/hw/mlx5/mlx5_ib.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/infiniband/hw/mlx5/mlx5_ib.h b/drivers/infiniband/hw/mlx5/mlx5_ib.h
index bf20a388eabe..f63bf204a7a1 100644
+++ b/drivers/infiniband/hw/mlx5/mlx5_ib.h

@@ -644,6 +644,7 @@ struct mlx5_ib_mr {
 	struct ib_umem *umem;
 
 	/* This is zero'd when the MR is allocated */
+	struct_group(cleared,
 	union {
 		/* Used only while the MR is in the cache */
 		struct {

@@ -691,12 +692,13 @@ struct mlx5_ib_mr {
 			bool is_odp_implicit;
 		};
 	};
+	);
 };
 
 /* Zero the fields in the mr that are variant depending on usage */
 static inline void mlx5_clear_mr(struct mlx5_ib_mr *mr)
 {
-	memset(mr->out, 0, sizeof(*mr) - offsetof(struct mlx5_ib_mr, out));
+	memset(&mr->cleared, 0, sizeof(mr->cleared));
 }

Why not use the memset_after(mr->umem) here?

I can certainly do that instead. In this series I've tended to opt
for groupings so the position of future struct member additions are
explicitly chosen. (i.e. reducing the chance that a zeroing of the new
member be a surprise.)

I saw the earlier RDMA patches where using other memset techniques
though? Were there flex arrays or something that made groups infeasible?

Which do you mean? When doing the conversions I tended to opt for
struct_group() since it provides more robust "intentionality". Strictly
speaking, the new memset helpers are doing field-spanning writes, but the
"clear to the end" pattern was so common it made sense to add the helpers,
as they're a bit less disruptive. It's totally up to you! :)

-- 
Kees Cook