netdev - Re: [PATCH v4 net-next 12/12] mlx5: support BIG TCP packets

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Date:   Fri, 6 May 2022 19:10:48 -0700
From:   Eric Dumazet <edumazet@...gle.com>
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>, Coco Li <lixiaoyan@...gle.com>,
        Tariq Toukan <tariqt@...dia.com>,
        Saeed Mahameed <saeedm@...dia.com>,
        Leon Romanovsky <leon@...nel.org>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH v4 net-next 12/12] mlx5: support BIG TCP packets

On Fri, May 6, 2022 at 6:54 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Fri, 6 May 2022 17:32:43 -0700 Eric Dumazet wrote:
> > On Fri, May 6, 2022 at 3:34 PM Jakub Kicinski <kuba@...nel.org> wrote:
> > >
> > > On Fri,  6 May 2022 08:30:48 -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
> > >
> > > In file included from ../include/linux/string.h:253,
> > >                  from ../arch/x86/include/asm/page_32.h:22,
> > >                  from ../arch/x86/include/asm/page.h:14,
> > >                  from ../arch/x86/include/asm/processor.h:19,
> > >                  from ../arch/x86/include/asm/timex.h:5,
> > >                  from ../include/linux/timex.h:65,
> > >                  from ../include/linux/time32.h:13,
> > >                  from ../include/linux/time.h:60,
> > >                  from ../include/linux/skbuff.h:15,
> > >                  from ../include/linux/tcp.h:17,
> > >                  from ../drivers/net/ethernet/mellanox/mlx5/core/en_tx.c:33:
> > > In function ‘fortify_memcpy_chk’,
> > >     inlined from ‘mlx5e_insert_vlan’ at ../drivers/net/ethernet/mellanox/mlx5/core/en_tx.c:104:2,
> > >     inlined from ‘mlx5e_sq_xmit_wqe’ at ../drivers/net/ethernet/mellanox/mlx5/core/en_tx.c:404:5:
> > > ../include/linux/fortify-string.h:328:25: warning: call to ‘__write_overflow_field’ declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Wattribute-warning]
> > >   328 |                         __write_overflow_field(p_size_field, size);
> > >       |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > In function ‘fortify_memcpy_chk’,
> > >     inlined from ‘mlx5e_sq_xmit_wqe’ at ../drivers/net/ethernet/mellanox/mlx5/core/en_tx.c:408:5:
> > > ../include/linux/fortify-string.h:328:25: warning: call to ‘__write_overflow_field’ declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Wattribute-warning]
> > >   328 |                         __write_overflow_field(p_size_field, size);
> > >       |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > In function ‘fortify_memcpy_chk’,
> > >     inlined from ‘mlx5i_sq_xmit’ at ../drivers/net/ethernet/mellanox/mlx5/core/en_tx.c:962:4:
> > > ../include/linux/fortify-string.h:328:25: warning: call to ‘__write_overflow_field’ declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Wattribute-warning]
> > >   328 |                         __write_overflow_field(p_size_field, size);
> > >       |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >
> > I guess these warnings show up before this BIG TCP patch ?
> >
> > I do not see any struct_group() being used in mlx5
> >
> > May I ask which compiler is used here, and what CONFIG_ option needs to be set ?
> >
> > Thanks.
>
> Without our patches drivers/net/ethernet/mellanox/mlx5/core/ builds
> cleanly. Gotta be the new W=1 filed overflow warnings, let's bother
> Kees.

Note that inline_hdr.start is a 2 byte array.

Obviously mlx5 driver copies more than 2 bytes of inlined headers.

mlx5e_insert_vlan(eseg->inline_hdr.start, skb, attr->ihs)
is called already with attr->ihs > 2

So it should already complain ?

static inline void mlx5e_insert_vlan(void *start, struct sk_buff *skb, u16 ihs)
{
   struct vlan_ethhdr *vhdr = (struct vlan_ethhdr *)start;
   int cpy1_sz = 2 * ETH_ALEN;
   int cpy2_sz = ihs - cpy1_sz;

    memcpy(&vhdr->addrs, skb->data, cpy1_sz);
    vhdr->h_vlan_proto = skb->vlan_proto;
    vhdr->h_vlan_TCI = cpu_to_be16(skb_vlan_tag_get(skb));
    memcpy(&vhdr->h_vlan_encapsulated_proto, skb->data + cpy1_sz,
cpy2_sz);  // Here, more than 2 bytes are copied already
}