netdev - Re: [PATCH v5 net-next 13/13] mlx5: support BIG TCP packets

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Date:   Tue, 10 May 2022 08:49:03 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Paolo Abeni <pabeni@...hat.com>,
        netdev <netdev@...r.kernel.org>,
        Alexander Duyck <alexanderduyck@...com>,
        Coco Li <lixiaoyan@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Tariq Toukan <tariqt@...dia.com>,
        Saeed Mahameed <saeedm@...dia.com>,
        Leon Romanovsky <leon@...nel.org>
Subject: Re: [PATCH v5 net-next 13/13] mlx5: support BIG TCP packets

On Mon, May 09, 2022 at 06:38:53PM -0700, Jakub Kicinski wrote:
> On Mon,  9 May 2022 15:21:49 -0700 Eric Dumazet wrote:
> > From: Coco Li <lixiaoyan@...gle.com>
> > 
> > mlx5 supports LSOv2.
> > 
> > IPv6 gro/tcp stacks insert a temporary Hop-by-Hop header
> > with JUMBO TLV for big packets.
> > 
> > We need to ignore/skip this HBH header when populating TX descriptor.
> > 
> > Note that ipv6_has_hopopt_jumbo() only recognizes very specific packet
> > layout, thus mlx5e_sq_xmit_wqe() is taking care of this layout only.
> > 
> > v2: clear hopbyhop in mlx5e_tx_get_gso_ihs()
> > v4: fix compile error for CONFIG_MLX5_CORE_IPOIB=y
> > 
> > Signed-off-by: Coco Li <lixiaoyan@...gle.com>
> > Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> > Reviewed-by: Tariq Toukan <tariqt@...dia.com>
> > Cc: Saeed Mahameed <saeedm@...dia.com>
> > Cc: Leon Romanovsky <leon@...nel.org>
> 
> So we're leaving the warning for Kees to deal with?
> 
> Kees is there some form of "I know what I'm doing" cast 
> that you could sneak us under the table?

Right now, it's switching that memcpy to __builtin_memcpy(), but I'll
send a patch that'll create an unsafe_memcpy() macro that does the right
things vs kasan, fortify, etc.

-- 
Kees Cook