test_bpf: Add backward jump test case

Currently the testsuite does not have a test case with a backward jump.
The s390x JIT (kernel 4.0) had a bug in that area.
So add one new test case for this now.

Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 16 insertions, 0 deletions

diff --git a/lib/test_bpf.c b/lib/test_bpf.c
index aaa0a40a7eb3..9b012a811ee1 100644
--- a/lib/test_bpf.c
+++ b/lib/test_bpf.c
@@ -3940,6 +3940,22 @@ static struct bpf_test tests[] = {
                 { },
                 { { 0, 1 } },
         },
+        /* BPF_JMP | BPF_JGT | BPF_K jump backwards */
+        {
+                "JMP_JGT_K: if (3 > 2) return 1 (jump backwards)",
+                .u.insns_int = {
+                        BPF_JMP_IMM(BPF_JA, 0, 0, 2), /* goto start */
+                        BPF_ALU32_IMM(BPF_MOV, R0, 1), /* out: */
+                        BPF_EXIT_INSN(),
+                        BPF_ALU32_IMM(BPF_MOV, R0, 0), /* start: */
+                        BPF_LD_IMM64(R1, 3), /* note: this takes 2 insns */
+                        BPF_JMP_IMM(BPF_JGT, R1, 2, -6), /* goto out */
+                        BPF_EXIT_INSN(),
+                },
+                INTERNAL,
+                { },
+                { { 0, 1 } },
+        },
         {
                 "JMP_JGE_K: if (3 >= 3) return 1",
                 .u.insns_int = {