netdev - [PATCH] selftests/bpf: Fix count write in testapp_xdp_metadata

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Message-Id: <20250829-selftests-bpf-xsk_regression_fix-v1-1-5f5acdb9fe6b@suse.com>
Date: Fri, 29 Aug 2025 16:33:49 -0300
From: Ricardo B. Marlière <rbm@...e.com>
To: Björn Töpel <bjorn@...nel.org>, 
 Magnus Karlsson <magnus.karlsson@...el.com>, 
 Maciej Fijalkowski <maciej.fijalkowski@...el.com>, 
 Jonathan Lemon <jonathan.lemon@...il.com>, 
 Stanislav Fomichev <sdf@...ichev.me>, Alexei Starovoitov <ast@...nel.org>, 
 Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, 
 Martin KaFai Lau <martin.lau@...ux.dev>, 
 Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
 Yonghong Song <yonghong.song@...ux.dev>, 
 John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, 
 Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, 
 Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>, 
 "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
 Jesper Dangaard Brouer <hawk@...nel.org>, 
 Tushar Vyavahare <tushar.vyavahare@...el.com>
Cc: netdev@...r.kernel.org, bpf@...r.kernel.org, 
 linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Ricardo B. Marlière <rbm@...e.com>
Subject: [PATCH] selftests/bpf: Fix count write in
 testapp_xdp_metadata_copy()

Commit 4b302092553c ("selftests/xsk: Add tail adjustment tests and support
check") added a new global to xsk_xdp_progs.c, but left out the access in
the testapp_xdp_metadata_copy() function. Since bpf_map_update_elem() will
write to the whole bss section, it gets truncated. Fix by writing to
skel_rx->bss->count directly.

Fixes: 4b302092553c ("selftests/xsk: Add tail adjustment tests and support check")
Signed-off-by: Ricardo B. Marlière <rbm@...e.com>
---
 tools/testing/selftests/bpf/xskxceiver.c | 14 +-------------
 1 file changed, 1 insertion(+), 13 deletions(-)

diff --git a/tools/testing/selftests/bpf/xskxceiver.c b/tools/testing/selftests/bpf/xskxceiver.c
index a29de0713f19f05ef49a52e3824bb58a30565e87..352adc8df2d1cd777c823c5a89f1720ee043f342 100644
--- a/tools/testing/selftests/bpf/xskxceiver.c
+++ b/tools/testing/selftests/bpf/xskxceiver.c
@@ -2276,25 +2276,13 @@ static int testapp_xdp_metadata_copy(struct test_spec *test)
 {
 	struct xsk_xdp_progs *skel_rx = test->ifobj_rx->xdp_progs;
 	struct xsk_xdp_progs *skel_tx = test->ifobj_tx->xdp_progs;
-	struct bpf_map *data_map;
-	int count = 0;
-	int key = 0;

 	test_spec_set_xdp_prog(test, skel_rx->progs.xsk_xdp_populate_metadata,
 			       skel_tx->progs.xsk_xdp_populate_metadata,
 			       skel_rx->maps.xsk, skel_tx->maps.xsk);
 	test->ifobj_rx->use_metadata = true;

-	data_map = bpf_object__find_map_by_name(skel_rx->obj, "xsk_xdp_.bss");
-	if (!data_map || !bpf_map__is_internal(data_map)) {
-		ksft_print_msg("Error: could not find bss section of XDP program\n");
-		return TEST_FAILURE;
-	}
-
-	if (bpf_map_update_elem(bpf_map__fd(data_map), &key, &count, BPF_ANY)) {
-		ksft_print_msg("Error: could not update count element\n");
-		return TEST_FAILURE;
-	}
+	skel_rx->bss->count = 0;

 	return testapp_validate_traffic(test);
 }

---
base-commit: 5b6d6fe1ca7b712c74f78426bb23c465fd34b322
change-id: 20250829-selftests-bpf-xsk_regression_fix-674d292e4d2a

Best regards,
-- 
Ricardo B. Marlière <rbm@...e.com>