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Mon, 21 Sep 2020 08:46:58 -0700 (PDT) Date: Mon, 21 Sep 2020 08:46:53 -0700 From: John Fastabend To: Tony Ambardar , Alexei Starovoitov , Daniel Borkmann Cc: Tony Ambardar , netdev@vger.kernel.org, bpf@vger.kernel.org, linux-arch@vger.kernel.org, Arnd Bergmann Message-ID: <5f68caed36dab_17370208e9@john-XPS-13-9370.notmuch> In-Reply-To: <90f81508ecc57bc0da318e0fe0f45cfe49b17ea7.1600417359.git.Tony.Ambardar@gmail.com> References: <90f81508ecc57bc0da318e0fe0f45cfe49b17ea7.1600417359.git.Tony.Ambardar@gmail.com> Subject: RE: [PATCH bpf v1 3/3] libbpf: fix native endian assumption when parsing BTF Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org Tony Ambardar wrote: > Code in btf__parse_raw() fails to detect raw BTF of non-native endianness > and assumes it must be ELF data, which then fails to parse as ELF and > yields a misleading error message: > > root:/# bpftool btf dump file /sys/kernel/btf/vmlinux > libbpf: failed to get EHDR from /sys/kernel/btf/vmlinux > > For example, this could occur after cross-compiling a BTF-enabled kernel > for a target with non-native endianness, which is currently unsupported. > > Check for correct endianness and emit a clearer error message: > > root:/# bpftool btf dump file /sys/kernel/btf/vmlinux > libbpf: non-native BTF endianness is not supported > > Fixes: 94a1fedd63ed ("libbpf: Add btf__parse_raw() and generic btf__parse() APIs") > > Signed-off-by: Tony Ambardar > --- > tools/lib/bpf/btf.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c > index 7dfca7016aaa..6bdbc389b493 100644 > --- a/tools/lib/bpf/btf.c > +++ b/tools/lib/bpf/btf.c > @@ -659,6 +659,12 @@ struct btf *btf__parse_raw(const char *path) > err = -EIO; > goto err_out; > } > + if (magic == __bswap_16(BTF_MAGIC)) { > + /* non-native endian raw BTF */ > + pr_warn("non-native BTF endianness is not supported\n"); > + err = -LIBBPF_ERRNO__ENDIAN; > + goto err_out; > + } > if (magic != BTF_MAGIC) { > /* definitely not a raw BTF */ > err = -EPROTO; > -- > 2.25.1 > Acked-by: John Fastabend