From: Alexander Lobakin <aleksander.lobakin@intel.com>
To: Michal Schmidt <mschmidt@redhat.com>
Cc: "Alexei Starovoitov" <ast@kernel.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
"David S. Miller" <davem@davemloft.net>,
"Jakub Kicinski" <kuba@kernel.org>,
"Jesper Dangaard Brouer" <hawk@kernel.org>,
"John Fastabend" <john.fastabend@gmail.com>,
"Andrii Nakryiko" <andrii@kernel.org>,
"Martin KaFai Lau" <martin.lau@linux.dev>,
"Eduard Zingerman" <eddyz87@gmail.com>,
"Song Liu" <song@kernel.org>,
"Yonghong Song" <yonghong.song@linux.dev>,
"KP Singh" <kpsingh@kernel.org>,
"Stanislav Fomichev" <sdf@google.com>,
"Hao Luo" <haoluo@google.com>, "Jiri Olsa" <jolsa@kernel.org>,
"Mykola Lysenko" <mykolal@fb.com>,
"Shuah Khan" <shuah@kernel.org>,
"Toke Høiland-Jørgensen" <toke@redhat.com>,
netdev@vger.kernel.org, bpf@vger.kernel.org,
linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH net] selftests/bpf: fix pointer arithmetic in test_xdp_do_redirect
Date: Tue, 7 May 2024 10:47:03 +0200 [thread overview]
Message-ID: <327aafc5-2bea-4cc2-9ada-9320146b5e28@intel.com> (raw)
In-Reply-To: <20240506145023.214248-1-mschmidt@redhat.com>
From: Michal Schmidt <mschmidt@redhat.com>
Date: Mon, 6 May 2024 16:50:22 +0200
> Cast operation has a higher precedence than addition. The code here
> wants to zero the 2nd half of the 64-bit metadata, but due to a pointer
> arithmetic mistake, it writes the zero at offset 16 instead.
>
> Just adding parentheses around "data + 4" would fix this, but I think
> this will be slightly better readable with array syntax.
>
> I was unable to test this with tools/testing/selftests/bpf/vmtest.sh,
> because my glibc is newer than glibc in the provided VM image.
> So I just checked the difference in the compiled code.
> objdump -S tools/testing/selftests/bpf/xdp_do_redirect.test.o:
> - *((__u32 *)data) = 0x42; /* metadata test value */
> + ((__u32 *)data)[0] = 0x42; /* metadata test value */
> be7: 48 8d 85 30 fc ff ff lea -0x3d0(%rbp),%rax
> bee: c7 00 42 00 00 00 movl $0x42,(%rax)
> - *((__u32 *)data + 4) = 0;
> + ((__u32 *)data)[1] = 0;
> bf4: 48 8d 85 30 fc ff ff lea -0x3d0(%rbp),%rax
> - bfb: 48 83 c0 10 add $0x10,%rax
> + bfb: 48 83 c0 04 add $0x4,%rax
> bff: c7 00 00 00 00 00 movl $0x0,(%rax)
>
> Fixes: 5640b6d89434 ("selftests/bpf: fix "metadata marker" getting overwritten by the netstack")
> Signed-off-by: Michal Schmidt <mschmidt@redhat.com>
> ---
> tools/testing/selftests/bpf/prog_tests/xdp_do_redirect.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_do_redirect.c b/tools/testing/selftests/bpf/prog_tests/xdp_do_redirect.c
> index 498d3bdaa4b0..bad0ea167be7 100644
> --- a/tools/testing/selftests/bpf/prog_tests/xdp_do_redirect.c
> +++ b/tools/testing/selftests/bpf/prog_tests/xdp_do_redirect.c
> @@ -107,8 +107,8 @@ void test_xdp_do_redirect(void)
> .attach_point = BPF_TC_INGRESS);
>
> memcpy(&data[sizeof(__u64)], &pkt_udp, sizeof(pkt_udp));
> - *((__u32 *)data) = 0x42; /* metadata test value */
> - *((__u32 *)data + 4) = 0;
> + ((__u32 *)data)[0] = 0x42; /* metadata test value */
> + ((__u32 *)data)[1] = 0;
Uff sorry. I was a bit in hurry to fix BPF CI and did this braino :z
I know pointer arithms obviously :D
I'd give a Rev-by, but it was applied already. Thanks!
>
> skel = test_xdp_do_redirect__open();
> if (!ASSERT_OK_PTR(skel, "skel"))
Thanks,
Olek
prev parent reply other threads:[~2024-05-07 8:47 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-06 14:50 [PATCH net] selftests/bpf: fix pointer arithmetic in test_xdp_do_redirect Michal Schmidt
2024-05-06 19:47 ` Toke Høiland-Jørgensen
2024-05-06 21:00 ` patchwork-bot+netdevbpf
2024-05-07 8:47 ` Alexander Lobakin [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=327aafc5-2bea-4cc2-9ada-9320146b5e28@intel.com \
--to=aleksander.lobakin@intel.com \
--cc=andrii@kernel.org \
--cc=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=daniel@iogearbox.net \
--cc=davem@davemloft.net \
--cc=eddyz87@gmail.com \
--cc=haoluo@google.com \
--cc=hawk@kernel.org \
--cc=john.fastabend@gmail.com \
--cc=jolsa@kernel.org \
--cc=kpsingh@kernel.org \
--cc=kuba@kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-kselftest@vger.kernel.org \
--cc=martin.lau@linux.dev \
--cc=mschmidt@redhat.com \
--cc=mykolal@fb.com \
--cc=netdev@vger.kernel.org \
--cc=sdf@google.com \
--cc=shuah@kernel.org \
--cc=song@kernel.org \
--cc=toke@redhat.com \
--cc=yonghong.song@linux.dev \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).