linux-kernel - [PATCH bpf-next v3 2/2] selftests/bpf: check null propagation only neither reg is PTR_TO_BTF

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Message-Id: <20221222024414.29539-2-sunhao.th@gmail.com>
Date:   Thu, 22 Dec 2022 10:44:14 +0800
From:   Hao Sun <sunhao.th@...il.com>
To:     bpf@...r.kernel.org
Cc:     ast@...nel.org, daniel@...earbox.net, john.fastabend@...il.com,
        andrii@...nel.org, martin.lau@...ux.dev, song@...nel.org,
        yhs@...com, kpsingh@...nel.org, sdf@...gle.com, haoluo@...gle.com,
        jolsa@...nel.org, davem@...emloft.net,
        linux-kernel@...r.kernel.org, Hao Sun <sunhao.th@...il.com>,
        Martin KaFai Lau <martin.lau@...nel.org>
Subject: [PATCH bpf-next v3 2/2] selftests/bpf: check null propagation only neither reg is PTR_TO_BTF_ID

Verify that nullness information is not porpagated in the branches
of register to register JEQ and JNE operations if one of them is
PTR_TO_BTF_ID. Implement this in C level so we can use CO-RE.

Signed-off-by: Hao Sun <sunhao.th@...il.com>
Suggested-by: Martin KaFai Lau <martin.lau@...nel.org>
---
 .../bpf/prog_tests/jeq_infer_not_null.c       |  9 ++++
 .../bpf/progs/jeq_infer_not_null_fail.c       | 42 +++++++++++++++++++
 2 files changed, 51 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/jeq_infer_not_null.c
 create mode 100644 tools/testing/selftests/bpf/progs/jeq_infer_not_null_fail.c

diff --git a/tools/testing/selftests/bpf/prog_tests/jeq_infer_not_null.c b/tools/testing/selftests/bpf/prog_tests/jeq_infer_not_null.c
new file mode 100644
index 000000000000..3add34df5767
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/jeq_infer_not_null.c
@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <test_progs.h>
+#include "jeq_infer_not_null_fail.skel.h"
+
+void test_jeq_infer_not_null(void)
+{
+	RUN_TESTS(jeq_infer_not_null_fail);
+}
diff --git a/tools/testing/selftests/bpf/progs/jeq_infer_not_null_fail.c b/tools/testing/selftests/bpf/progs/jeq_infer_not_null_fail.c
new file mode 100644
index 000000000000..f46965053acb
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/jeq_infer_not_null_fail.c
@@ -0,0 +1,42 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include "bpf_misc.h"
+
+char _license[] SEC("license") = "GPL";
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__uint(max_entries, 1);
+	__type(key, u64);
+	__type(value, u64);
+} m_hash SEC(".maps");
+
+SEC("?raw_tp")
+__failure __msg("R8 invalid mem access 'map_value_or_null")
+int jeq_infer_not_null_ptr_to_btfid(void *ctx)
+{
+	struct bpf_map *map = (struct bpf_map *)&m_hash;
+	struct bpf_map *inner_map = map->inner_map_meta;
+	u64 key = 0, ret = 0, *val;
+
+	val = bpf_map_lookup_elem(map, &key);
+	/* Do not mark ptr as non-null if one of them is
+	 * PTR_TO_BTF_ID (R9), reject because of invalid
+	 * access to map value (R8).
+	 *
+	 * Here, we need to inline those insns to access
+	 * R8 directly, since compiler may use other reg
+	 * once it figures out val==inner_map.
+	 */
+	asm volatile("r8 = %[val];\n"
+		     "r9 = %[inner_map];\n"
+		     "if r8 != r9 goto +1;\n"
+		     "%[ret] = *(u64 *)(r8 +0);\n"
+		     : [ret] "+r"(ret)
+		     : [inner_map] "r"(inner_map), [val] "r"(val)
+		     : "r8", "r9");
+
+	return ret;
+}
-- 
2.39.0