Subject: Re: [PATCH v2 56/63] RDMA/mlx5: Use struct_group() to zero struct mlx5_ib_mr

From: Jason Gunthorpe <[email-masked]>
Date: Thu, 19 Aug 2021 09:27:16 -0300

On Tue, Aug 17, 2021 at 11:05:26PM -0700, Kees Cook wrote:
> 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 <[email-masked]>
> Cc: Doug Ledford <[email-masked]>
> Cc: Jason Gunthorpe <[email-masked]>
> Cc: [email-masked]
> Signed-off-by: Kees Cook <[email-masked]>
> ---
>  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
> --- a/drivers/infiniband/hw/mlx5/mlx5_ib.h
> +++ 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?

Jason