selftests/bpf: tests for jmp to 1st insn

Add 2 tests that check JIT code generation to jumps to 1st insn.
1st test is similar to syzbot reproducer.
The backwards branch is never taken at runtime.
2nd test has branch to 1st insn that executes.
The test is written as two bpf functions, since it's not possible
to construct valid single bpf program that jumps to 1st insn.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>

diff --git a/tools/testing/selftests/bpf/verifier/loops1.c b/tools/testing/selftests/bpf/verifier/loops1.c
index 5e980a5ab69deb857291889abb616d92507c852c..1fc4e61e9f9f0ba84b5d3329d1168446162d3cf1 100644 (file)
--- a/tools/testing/selftests/bpf/verifier/loops1.c
+++ b/tools/testing/selftests/bpf/verifier/loops1.c
@@ -159,3 +159,31 @@
        .errstr = "loop detected",
        .prog_type = BPF_PROG_TYPE_TRACEPOINT,
 },
+{
+       "not-taken loop with back jump to 1st insn",
+       .insns = {
+       BPF_MOV64_IMM(BPF_REG_0, 123),
+       BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 4, -2),
+       BPF_EXIT_INSN(),
+       },
+       .result = ACCEPT,
+       .prog_type = BPF_PROG_TYPE_XDP,
+       .retval = 123,
+},
+{
+       "taken loop with back jump to 1st insn",
+       .insns = {
+       BPF_MOV64_IMM(BPF_REG_1, 10),
+       BPF_MOV64_IMM(BPF_REG_2, 0),
+       BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 1, 0, 1),
+       BPF_EXIT_INSN(),
+       BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_1),
+       BPF_ALU64_IMM(BPF_SUB, BPF_REG_1, 1),
+       BPF_JMP_IMM(BPF_JNE, BPF_REG_1, 0, -3),
+       BPF_MOV64_REG(BPF_REG_0, BPF_REG_2),
+       BPF_EXIT_INSN(),
+       },
+       .result = ACCEPT,
+       .prog_type = BPF_PROG_TYPE_XDP,
+       .retval = 55,
+},