From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: Jesper Dangaard Brouer <brouer@redhat.com>, bpf@vger.kernel.org
Cc: jakub.kicinski@netronome.com, netdev@vger.kernel.org,
Jesper Dangaard Brouer <brouer@redhat.com>,
Daniel Borkmann <borkmann@iogearbox.net>,
danieltimlee@gmail.com,
Alexei Starovoitov <alexei.starovoitov@gmail.com>
Subject: Re: [bpf PATCH] samples/bpf: fix broken xdp_rxq_info due to map order assumptions
Date: Mon, 02 Dec 2019 14:02:27 +0100 [thread overview]
Message-ID: <87k17ericc.fsf@toke.dk> (raw)
In-Reply-To: <157529025128.29832.5953245340679936909.stgit@firesoul>
Jesper Dangaard Brouer <brouer@redhat.com> writes:
> In the days of using bpf_load.c the order in which the 'maps' sections
> were defines in BPF side (*_kern.c) file, were used by userspace side
> to identify the map via using the map order as an index. In effect the
> order-index is created based on the order the maps sections are stored
> in the ELF-object file, by the LLVM compiler.
>
> This have also carried over in libbpf via API bpf_map__next(NULL, obj)
> to extract maps in the order libbpf parsed the ELF-object file.
>
> When BTF based maps were introduced a new section type ".maps" were
> created. I found that the LLVM compiler doesn't create the ".maps"
> sections in the order they are defined in the C-file. The order in the
> ELF file is based on the order the map pointer is referenced in the code.
>
> This combination of changes lead to xdp_rxq_info mixing up the map
> file-descriptors in userspace, resulting in very broken behaviour, but
> without warning the user.
>
> This patch fix issue by instead using bpf_object__find_map_by_name()
> to find maps via their names. (Note, this is the ELF name, which can
> be longer than the name the kernel retains).
>
> Fixes: be5bca44aa6b ("samples: bpf: convert some XDP samples from bpf_load to libbpf")
> Fixes: 451d1dc886b5 ("samples: bpf: update map definition to new syntax BTF-defined map")
> Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
next prev parent reply other threads:[~2019-12-02 13:02 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-02 12:37 [bpf PATCH] samples/bpf: fix broken xdp_rxq_info due to map order assumptions Jesper Dangaard Brouer
2019-12-02 13:02 ` Toke Høiland-Jørgensen [this message]
2019-12-02 17:35 ` Andrii Nakryiko
2019-12-05 1:54 ` Alexei Starovoitov
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