Commit cc4228d5 authored Jul 01, 2015 by Wang Nan Committed by Arnaldo Carvalho de Melo Aug 07, 2015

bpf tools: Check endianness and make libbpf fail early



Check endianness according to EHDR. Code is taken from
tools/perf/util/symbol-elf.c.

Libbpf doesn't magically convert missmatched endianness. Even if we swap
eBPF instructions to correct byte order, we are unable to deal with
endianness in code logical generated by LLVM.

Therefore, libbpf should simply reject missmatched ELF object, and let
LLVM to create good code.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: David Ahern <dsahern@gmail.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kaixu Xia <xiakaixu@huawei.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1435716878-189507-8-git-send-email-wangnan0@huawei.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

parent 6c956392

tools/lib/bpf/libbpf.c

+30 −0

Original line number	Diff line number	Diff line
		@@ -192,6 +192,34 @@ errout:
		return err;
		}

		static int
		bpf_object__check_endianness(struct bpf_object *obj)
		{
		static unsigned int const endian = 1;

		switch (obj->efile.ehdr.e_ident[EI_DATA]) {
		case ELFDATA2LSB:
		/* We are big endian, BPF obj is little endian. */
		if ((unsigned char const )&endian != 1)
		goto mismatch;
		break;

		case ELFDATA2MSB:
		/* We are little endian, BPF obj is big endian. */
		if ((unsigned char const )&endian != 0)
		goto mismatch;
		break;
		default:
		return -EINVAL;
		}

		return 0;

		mismatch:
		pr_warning("Error: endianness mismatch.\n");
		return -EINVAL;
		}

		static struct bpf_object *
		__bpf_object__open(const char path, void obj_buf, size_t obj_buf_sz)
		{
		@@ -208,6 +236,8 @@ __bpf_object__open(const char path, void obj_buf, size_t obj_buf_sz)

		if (bpf_object__elf_init(obj))
		goto out;
		if (bpf_object__check_endianness(obj))
		goto out;

		bpf_object__elf_finish(obj);
		return obj;

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