linux-hardening - Re: [PATCH net-next] netdevice: define and allocate &net_device _properly

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Date: Tue, 7 May 2024 17:30:55 +0200
From: Przemek Kitszel <przemyslaw.kitszel@...el.com>
To: Alexander Lobakin <aleksander.lobakin@...el.com>, "David S. Miller"
	<davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
	<kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
CC: Kees Cook <keescook@...omium.org>, "Gustavo A. R. Silva"
	<gustavoars@...nel.org>, Simon Horman <horms@...nel.org>,
	<nex.sw.ncis.osdt.itp.upstreaming@...el.com>,
	<linux-hardening@...r.kernel.org>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] netdevice: define and allocate &net_device
 _properly_

On 5/7/24 14:39, Alexander Lobakin wrote:
> In fact, this structure contains a flexible array at the end, but
> historically its size, alignment etc., is calculated manually.
> There are several instances of the structure embedded into other
> structures, but also there's ongoing effort to remove them and we
> could in the meantime declare &net_device properly.
> Declare the array explicitly, use struct_size() and store the array
> size inside the structure, so that __counted_by() can be applied.
> Don't use PTR_ALIGN(), as SLUB itself tries its best to ensure the
> allocated buffer is aligned to what the user expects.
> Also, change its alignment from %NETDEV_ALIGN to the cacheline size
> as per several suggestions on the netdev ML.
> 
> bloat-o-meter for vmlinux:
> 
> free_netdev                                  445     440      -5
> netdev_freemem                                24       -     -24
> alloc_netdev_mqs                            1481    1450     -31
> 
> On x86_64 with several NICs of different vendors, I was never able to
> get a &net_device pointer not aligned to the cacheline size after the
> change.
> 
> Signed-off-by: Alexander Lobakin <aleksander.lobakin@...el.com>
> ---
>   include/linux/netdevice.h | 12 +++++++-----
>   net/core/dev.c            | 31 +++++++------------------------
>   net/core/net-sysfs.c      |  2 +-
>   3 files changed, 15 insertions(+), 30 deletions(-)
> 

Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@...el.com>