netdev - Re: [PATCH net-next v2] netdevice: define and allocate &net_device _properly

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Message-ID: <202407090900.BD88B67AC5@keescook>
Date: Tue, 9 Jul 2024 09:02:05 -0700
From: Kees Cook <kees@...nel.org>
To: Breno Leitao <leitao@...ian.org>
Cc: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>, horms@...nel.org,
	nex.sw.ncis.osdt.itp.upstreaming@...el.com,
	linux-hardening@...r.kernel.org,
	Alexander Lobakin <aleksander.lobakin@...el.com>,
	Przemek Kitszel <przemyslaw.kitszel@...el.com>,
	Jiri Pirko <jiri@...nulli.us>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Daniel Borkmann <daniel@...earbox.net>,
	Lorenzo Bianconi <lorenzo@...nel.org>,
	Johannes Berg <johannes.berg@...el.com>,
	Heiner Kallweit <hkallweit1@...il.com>,
	"open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next v2] netdevice: define and allocate &net_device
 _properly_

On Tue, Jul 09, 2024 at 05:54:25AM -0700, Breno Leitao wrote:
> From: Alexander Lobakin <aleksander.lobakin@...el.com>
> 
> 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>
> Signed-off-by: Breno Leitao <leitao@...ian.org>
> Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@...el.com>

Nice! I'm glad the refactoring in other drivers got tackled so this
could happen. :)

Reviewed-by: Kees Cook <kees@...nel.org>

-- 
Kees Cook