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

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Date:   Thu, 19 Aug 2021 09:19:08 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Jason Gunthorpe <jgg@...pe.ca>
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 Thu, Aug 19, 2021 at 09:27:16AM -0300, Jason Gunthorpe wrote:
> 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?

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.)

-Kees

-- 
Kees Cook