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

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Date:   Tue, 7 Dec 2021 14:47:29 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Leon Romanovsky <leon@...nel.org>,
        Kees Cook <keescook@...omium.org>
Cc:     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 Sun, Nov 21, 2021 at 03:54:55PM +0200, Leon Romanovsky wrote:
> 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
> > +++ 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.

Kees?

Jason