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@gmail.com>
Suggested-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://lore.kernel.org/r/20221222024414.29539-2-sunhao.th@gmail.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

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 (file)
index 0000000..3add34d
--- /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 (file)
index 0000000..f469650
--- /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;
+}