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libbpf: Don't attempt to load unused subprog as an entry-point BPF program

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If BPF code contains unused BPF subprogram and there are no other subprogram
calls (which can realistically happen in real-world applications given
sufficiently smart Clang code optimizations), libbpf will erroneously assume
that subprograms are entry-point programs and will attempt to load them with
UNSPEC program type.

Fix by not relying on subcall instructions and rather detect it based on the
structure of BPF object's sections.

Fixes: 9a94f277c4 ("tools: libbpf: restore the ability to load programs from .text section")
Reported-by: Dmitrii Banshchikov <dbanschikov@fb.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20201107000251.256821-1-andrii@kernel.org
This commit is contained in:
Andrii Nakryiko
2020-11-06 16:02:51 -08:00
committed by Daniel Borkmann
parent 4e0396c595
commit 197afc6314
3 changed files with 40 additions and 10 deletions
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6
tools/testing/selftests/bpf/prog_tests/subprogs.c
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@@ -3,12 +3,14 @@
#include <test_progs.h>
#include <time.h>
#include "test_subprogs.skel.h"
#include "test_subprogs_unused.skel.h"
static int duration;
void test_subprogs(void)
{
struct test_subprogs *skel;
struct test_subprogs_unused *skel2;
int err;
skel = test_subprogs__open_and_load();
@@ -26,6 +28,10 @@ void test_subprogs(void)
CHECK(skel->bss->res3 != 19, "res3", "got %d, exp %d\n", skel->bss->res3, 19);
CHECK(skel->bss->res4 != 36, "res4", "got %d, exp %d\n", skel->bss->res4, 36);
skel2 = test_subprogs_unused__open_and_load();
ASSERT_OK_PTR(skel2, "unused_progs_skel");
test_subprogs_unused__destroy(skel2);
cleanup:
test_subprogs__destroy(skel);
}