From: Saeed Mahameed <saeed@kernel.org>
To: Kees Cook <keescook@chromium.org>
Cc: Leon Romanovsky <leon@kernel.org>,
"David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
netdev@vger.kernel.org, linux-rdma@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH] net/mlx5e: Avoid field-overflowing memcpy()
Date: Fri, 06 Aug 2021 15:57:40 -0700 [thread overview]
Message-ID: <b5f1c558fef468fe8550ebb5e77d36bf1d0971a7.camel@kernel.org> (raw)
In-Reply-To: <202108061541.976BE67@keescook>
On Fri, 2021-08-06 at 15:45 -0700, Kees Cook wrote:
> On Fri, Aug 06, 2021 at 03:17:56PM -0700, Saeed Mahameed wrote:
> > On Fri, 2021-08-06 at 14:50 -0700, Kees Cook wrote:
> > > [...]
> > > So, split the memcpy() so the compiler can reason about the buffer
> > > sizes.
> > >
> > > "pahole" shows no size nor member offset changes to struct > >
> > > mlx5e_tx_wqe
> > > nor struct mlx5e_umr_wqe. "objdump -d" shows no meaningful object
> > > code changes (i.e. only source line number induced differences and
> > > optimizations).
> >
> > spiting the memcpy doesn't induce any performance degradation ? extra
> > instruction to copy the 1st 2 bytes ?
>
> Not meaningfully, but strictly speaking, yes, it's a different series
> of
> instructions.
>
> > [...]
> > > --- a/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c
> > > +++ b/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c
> >
> > why only here ? mlx5 has at least 3 other places where we use this
> > unbound memcpy ..
>
> Can you point them out? I've been fixing only the ones I've been able
> to
> find through instrumentation (generally speaking, those with fixed
> sizes).
>
we will need to examine each change carefully to look for performance
degradation and maybe run some micro-benchmark tests in house before i
can ack this patch.
$ git grep -n "eseg->inline_hdr.start"
drivers/infiniband/hw/mlx5/wr.c:129: copysz = min_t(u64,
*cur_edge - (void *)eseg->inline_hdr.start,
drivers/infiniband/hw/mlx5/wr.c:131: memcpy(eseg-
>inline_hdr.start, pdata, copysz);
drivers/infiniband/hw/mlx5/wr.c:133:
sizeof(eseg->inline_hdr.start) + copysz, 16);
drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c:344:
memcpy(eseg->inline_hdr.start, xdptxd->data, MLX5E_XDP_MIN_INLINE);
drivers/net/ethernet/mellanox/mlx5/core/en_tx.c:510:
mlx5e_insert_vlan(eseg->inline_hdr.start, skb, attr->ihs);
drivers/net/ethernet/mellanox/mlx5/core/en_tx.c:514:
memcpy(eseg->inline_hdr.start, skb->data, attr->ihs);
drivers/net/ethernet/mellanox/mlx5/core/en_tx.c:1033:
memcpy(eseg->inline_hdr.start, skb->data, attr.ihs);
next prev parent reply other threads:[~2021-08-06 22:57 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-06 21:50 [PATCH] net/mlx5e: Avoid field-overflowing memcpy() Kees Cook
2021-08-06 22:17 ` Saeed Mahameed
2021-08-06 22:45 ` Kees Cook
2021-08-06 22:57 ` Saeed Mahameed [this message]
2021-11-15 22:16 Kees Cook
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