Re: [PATCH v6 0/2] lib: checksum: Fix issues with checksum tests

[Geert Uytterhoeven]

Hi Günter,

On Mon, Feb 12, 2024 at 6:13 PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> On Mon, Feb 12, 2024 at 12:26:08AM -0500, Charlie Jenkins wrote:
> > On Sun, Feb 11, 2024 at 11:18:36AM -0800, Guenter Roeck wrote:
> > > On 2/7/24 16:22, Charlie Jenkins wrote:
> > > > The ip_fast_csum and csum_ipv6_magic tests did not have the data
> > > > types properly casted, and improperly misaligned data.
> > > >
> > > > Signed-off-by: Charlie Jenkins <charlie@xxxxxxxxxxxx>
> > >
> > > I sorted out most of the problems with this version, but I still get:
> > >
> > >     # test_csum_ipv6_magic: ASSERTION FAILED at lib/checksum_kunit.c:513
> > >     Expected ( u64)csum_result == ( u64)expected, but
> > >         ( u64)csum_result == 16630 (0x40f6)
> > >         ( u64)expected == 65535 (0xffff)
> > >     not ok 5 test_csum_ipv6_magic
> > >
> > > on m68k:q800. This is suspicious because there is no 0xffff in
> > > expected_csum_ipv6_magic[]. With some debugging information:
> > >
> > > ####### num_tests=86 i=84 expect array size=84
> > > ####### MAX_LEN=512 WORD_ALIGNMENT=4 magic data size=42
> > >
> > > That means the loop
> > >
> > >     for (int i = 0; i < num_tests; i++) {
> > >             ...
> > >             expected = (__force __sum16)expected_csum_ipv6_magic[i];
> > >             ...
> > >     }
> > >
> > > will access data beyond the end of the expected_csum_ipv6_magic[] array,
> > > possibly because m68k doesn't pad struct csum_ipv6_magic_data to 44 bytes.
> >
> > Okay I will check that out.
> >
> > >
> > > In this context, is the comment about proto having to be 0 really true ?
> > > It seems to me that the calculated checksum must be identical on both
> > > little and big endian systems. After all, they need to be able to talk
> > > to each other.
> >
> > I agree, but I couldn't find a solution other than setting it to zero.
> > Maybe I am missing something simple...
> >
>
> Try the patch below on top of yours. It should work on both big and little
> endian systems.
>
> Key changes:
> - use random_buf directly instead of copying anything
> - no need to convert source / destination addresses
> - csum in the buffer is in network byte order and needs
>   to stay that way
> - len in the buffer is in network byte order and needs to be
>   converted to host byte order since that is expected by
>   csum_ipv6_magic()
> - the expected value is in host byte order and needs to be
>   converted to network byte order for comparison
> - protocol is just fine and converted by csum_ipv6_magic()
>   as needed

Thanks for your patch!

> --- a/lib/checksum_kunit.c
> +++ b/lib/checksum_kunit.c

> @@ -465,44 +468,36 @@ static void test_ip_fast_csum(struct kunit *test)
>         }
>  }
>
> +#define IPV6_NUM_TESTS ((MAX_LEN - sizeof(struct in6_addr) * 2 - sizeof(int) * 3) / WORD_ALIGNMENT)
> +
>  static void test_csum_ipv6_magic(struct kunit *test)
>  {
>  #if defined(CONFIG_NET)
> +       const struct in6_addr *saddr;
> +       const struct in6_addr *daddr;
> +       unsigned int len;
>         __sum16 csum_result, expected;
> -       struct csum_ipv6_magic_data {
> -               const struct in6_addr saddr;
> -               const struct in6_addr daddr;
> -               unsigned int len;
> -               __wsum csum;
> -               unsigned char proto;
> -       } data, *data_ptr;
> -       int num_tests = MAX_LEN / WORD_ALIGNMENT - sizeof(struct csum_ipv6_magic_data);
> +       unsigned char proto;
> +       unsigned int csum;
>
> -       for (int i = 0; i < num_tests; i++) {
> -               data_ptr = (struct csum_ipv6_magic_data *)(random_buf + (i * WORD_ALIGNMENT));
> +       const int daddr_offset = sizeof(struct in6_addr);
> +       const int len_offset = sizeof(struct in6_addr) + sizeof(struct in6_addr);
> +       const int csum_offset = sizeof(struct in6_addr) + sizeof(struct in6_addr) +
> +         sizeof(int);
> +       const int proto_offset = sizeof(struct in6_addr) + sizeof(struct in6_addr) +
> +         sizeof(int) * 2;

Please no manual offset calculations.
Please fix the csum_ipv6_magic_data structure definition instead.

>
> -               cpu_to_be32_array((__be32 *)&data.saddr, (const u32 *)&data_ptr->saddr,
> -                                 sizeof_field(struct csum_ipv6_magic_data, saddr) / 4);
> -               cpu_to_be32_array((__be32 *)&data.daddr, (const u32 *)&data_ptr->daddr,
> -                                 sizeof_field(struct csum_ipv6_magic_data, daddr) / 4);
> -               data.len = data_ptr->len;
> -               data.csum = (__force __wsum)htonl((__force u32)data_ptr->csum);
> -               /*
> -                * proto must be zero to be compatible between big-endian and
> -                * little-endian CPUs. On little-endian CPUs, proto is
> -                * converted to a big-endian 32-bit value before the checksum
> -                * operation. This causes proto to be in the most significant
> -                * 8 bits on a little-endian CPU. On big-endian CPUs proto will
> -                * remain in the least significant 8 bits. There does not exist
> -                * a transformation to an arbitrary proto that will allow
> -                * csum_ipv6_magic to return the same value on a big-endian and
> -                * little-endian CPUs.
> -                */
> -               data.proto = 0;
> -               csum_result = csum_ipv6_magic(&data.saddr, &data.daddr,
> -                                             data.len, data.proto,
> -                                             data.csum);
> -               expected = (__force __sum16)expected_csum_ipv6_magic[i];
> +       for (int i = 0; i < IPV6_NUM_TESTS; i++) {
> +               int index = i * WORD_ALIGNMENT;
> +
> +               saddr = (const struct in6_addr *)(random_buf + index);
> +               daddr = (const struct in6_addr *)(random_buf + index + daddr_offset);
> +               len = ntohl(*(unsigned int *)(random_buf + index + len_offset));
> +               csum = *(unsigned int *)(random_buf + index + csum_offset);
> +               proto = *(random_buf + index + proto_offset);
> +
> +               csum_result = csum_ipv6_magic(saddr, daddr, len, proto, csum);
> +               expected = (__force __sum16)htons(expected_csum_ipv6_magic[i]);
>                 CHECK_EQ(csum_result, expected);
>         }
>  #endif /* !CONFIG_NET */

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68korg

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