bpf: Selftests, verifier case for non null pointer map value branch

When we have pointer type that is known to be non-null we only follow
the non-null branch. This adds tests to cover the map_value pointer
returned from a map lookup. To force an error if both branches are
followed we do an ALU op on R10.

Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/159009168650.6313.7434084136067263554.stgit@john-Precision-5820-Tower

diff --git a/tools/testing/selftests/bpf/verifier/value_or_null.c b/tools/testing/selftests/bpf/verifier/value_or_null.c
index 860d4a71cd83a10f7116ada1961da382970de9cd..3ecb70a3d93970425413dee6cd402bdcdf6c4ed9 100644 (file)
--- a/tools/testing/selftests/bpf/verifier/value_or_null.c
+++ b/tools/testing/selftests/bpf/verifier/value_or_null.c
@@ -150,3 +150,22 @@
        .result_unpriv = REJECT,
        .flags = F_NEEDS_EFFICIENT_UNALIGNED_ACCESS,
 },
+{
+       "map lookup and null branch prediction",
+       .insns = {
+       BPF_MOV64_IMM(BPF_REG_1, 10),
+       BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_1, -8),
+       BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
+       BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),
+       BPF_LD_MAP_FD(BPF_REG_1, 0),
+       BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),
+       BPF_MOV64_REG(BPF_REG_6, BPF_REG_0),
+       BPF_JMP_IMM(BPF_JEQ, BPF_REG_6, 0, 2),
+       BPF_JMP_IMM(BPF_JNE, BPF_REG_6, 0, 1),
+       BPF_ALU64_IMM(BPF_ADD, BPF_REG_10, 10),
+       BPF_EXIT_INSN(),
+       },
+       .fixup_map_hash_8b = { 4 },
+       .prog_type = BPF_PROG_TYPE_SCHED_CLS,
+       .result = ACCEPT,
+},