linux-hardening - Re: [PATCH] RDMA/mlx5: Use memset_after() to zero struct mlx5_ib

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Date:   Sun, 21 Nov 2021 15:54:55 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Doug Ledford <dledford@...hat.com>, Jason Gunthorpe <jgg@...pe.ca>,
        linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] RDMA/mlx5: Use memset_after() to zero struct mlx5_ib_mr

On Thu, Nov 18, 2021 at 12:31:38PM -0800, 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.
> 
> Use memset_after() to zero the end of struct mlx5_ib_mr that should
> be initialized.
> 
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  drivers/infiniband/hw/mlx5/mlx5_ib.h | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/infiniband/hw/mlx5/mlx5_ib.h b/drivers/infiniband/hw/mlx5/mlx5_ib.h
> index e636e954f6bf..af94c9fe8753 100644
> --- a/drivers/infiniband/hw/mlx5/mlx5_ib.h
> +++ b/drivers/infiniband/hw/mlx5/mlx5_ib.h
> @@ -665,8 +665,7 @@ struct mlx5_ib_mr {
>  	/* User MR data */
>  	struct mlx5_cache_ent *cache_ent;
>  	struct ib_umem *umem;
> -
> -	/* This is zero'd when the MR is allocated */
> +	/* Everything after umem is zero'd when the MR is allocated */
>  	union {
>  		/* Used only while the MR is in the cache */
>  		struct {
> @@ -718,7 +717,7 @@ struct mlx5_ib_mr {
>  /* 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_after(mr, 0, umem);

I think that it is not equivalent change and you need "memset_after(mr, 0, cache_ent);"
to clear umem pointer too.

>  }
>  
>  static inline bool is_odp_mr(struct mlx5_ib_mr *mr)
> -- 
> 2.30.2
>