linux-kernel - Re: [PATCH] nvme-tcp: Fix implicit padding in struct nvme_tcp_term

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Message-ID: <CAMuHMdWMih6kqSZaKq5p+UVOjTOCWdeUeif2y2ugtgcVOPmzyQ@mail.gmail.com>
Date:   Mon, 20 Mar 2023 16:39:37 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Caleb Sander <csander@...estorage.com>
Cc:     Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...com>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        Arnd Bergmann <arnd@...db.de>, linux-nvme@...ts.infradead.org,
        linux-m68k@...ts.linux-m68k.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nvme-tcp: Fix implicit padding in struct nvme_tcp_term_pdu

Hi Caleb,

On Mon, Mar 20, 2023 at 4:34 PM Caleb Sander <csander@...estorage.com> wrote:
> The nvme_tcp_term_pdu definition needs to be updated anyways to match
> the spec. FEI is at offset 10, so it isn't 4-byte-aligned. I think we
> have gotten away with this so far because the NVMe/TCP driver never
> sends H2CTermReq and doesn't interpret C2HTermReq.
> Mirroring numdl/numdu in nvme_get_log_page_command, the definition
> should look something like:
> struct nvme_tcp_term_pdu {
>         struct nvme_tcp_hdr hdr;
>         __le16 fes;
>         __le16 feil;
>         __le16 feiu;
>         __u8 rsvd[10];
> };

Great, so it was compliant only on m68k? ;-)

> On Mon, Mar 20, 2023 at 4:29 AM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> >
> > On m68k:
> >
> >     drivers/nvme/host/tcp.c: In function ‘nvme_tcp_init_module’:
> >     include/linux/compiler_types.h:397:38: error: call to ‘__compiletime_assert_723’ declared with attribute error: BUILD_BUG_ON failed: sizeof(struct nvme_tcp_term_pdu) != 24
> >
> > Indeed, on m68k the minimum alignment is 2 bytes, not 4 bytes, thus
> > triggering the check added in commit 7e87965d3807ab1f ("nvme-tcp: add
> > nvme-tcp pdu size build protection"), and indicating that NVMe over
> > Fabrics TCP on m68k must be incompatible with other platforms.
> >
> > Fix this by adding explicit padding.
> >
> > Fixes: fc221d05447aa6db ("nvme-tcp: Add protocol header")
> > Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> > ---
> >  include/linux/nvme-tcp.h | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/include/linux/nvme-tcp.h b/include/linux/nvme-tcp.h
> > index 75470159a194d97f..ba8f82672e39730f 100644
> > --- a/include/linux/nvme-tcp.h
> > +++ b/include/linux/nvme-tcp.h
> > @@ -115,6 +115,7 @@ struct nvme_tcp_icresp_pdu {
> >  struct nvme_tcp_term_pdu {
> >         struct nvme_tcp_hdr     hdr;
> >         __le16                  fes;
> > +       __u8                    rsvd2[2];
> >         __le32                  fei;
> >         __u8                    rsvd[8];
> >  };

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds