linux-hardening - Re: [PATCH v2 56/63] RDMA/mlx5: Use struct_group() to zero struct mlx5_ib

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Message-ID: <20210819122716.GP543798@ziepe.ca>
Date:   Thu, 19 Aug 2021 09:27:16 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Kees Cook <keescook@...omium.org>
Cc:     linux-kernel@...r.kernel.org, Leon Romanovsky <leon@...nel.org>,
        Doug Ledford <dledford@...hat.com>, linux-rdma@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-staging@...ts.linux.dev,
        linux-block@...r.kernel.org, linux-kbuild@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2 56/63] RDMA/mlx5: Use struct_group() to zero struct
 mlx5_ib_mr

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 <leon@...nel.org>
> Cc: Doug Ledford <dledford@...hat.com>
> Cc: Jason Gunthorpe <jgg@...pe.ca>
> Cc: linux-rdma@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  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