selftests/bpf: Skip callback tests if jit is disabled in test_verifier

If CONFIG_BPF_JIT_ALWAYS_ON is not set and bpf_jit_enable is 0, there
exist 6 failed tests.

  [root@linux bpf]# echo 0 > /proc/sys/net/core/bpf_jit_enable
  [root@linux bpf]# echo 0 > /proc/sys/kernel/unprivileged_bpf_disabled
  [root@linux bpf]# ./test_verifier | grep FAIL
  torvalds#106/p inline simple bpf_loop call FAIL
  torvalds#107/p don't inline bpf_loop call, flags non-zero FAIL
  torvalds#108/p don't inline bpf_loop call, callback non-constant FAIL
  torvalds#109/p bpf_loop_inline and a dead func FAIL
  torvalds#110/p bpf_loop_inline stack locations for loop vars FAIL
  torvalds#111/p inline bpf_loop call in a big program FAIL
  Summary: 768 PASSED, 15 SKIPPED, 6 FAILED

The test log shows that callbacks are not allowed in non-JITed programs,
interpreter doesn't support them yet, thus these tests should be skipped
if jit is disabled.

Add an explicit flag F_NEEDS_JIT_ENABLED to those tests to mark that they
require JIT enabled in bpf_loop_inline.c, check the flag and jit_disabled
at the beginning of do_test_single() to handle this case.

With this patch:

  [root@linux bpf]# echo 0 > /proc/sys/net/core/bpf_jit_enable
  [root@linux bpf]# echo 0 > /proc/sys/kernel/unprivileged_bpf_disabled
  [root@linux bpf]# ./test_verifier | grep FAIL
  Summary: 768 PASSED, 21 SKIPPED, 0 FAILED

Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240123090351.2207-3-yangtiezhu@loongson.cn

tools/testing/selftests/bpf/test_verifier.c

@@ -67,13 +67,15 @@
 
 #define F_NEEDS_EFFICIENT_UNALIGNED_ACCESS	(1 << 0)
 #define F_LOAD_WITH_STRICT_ALIGNMENT		(1 << 1)
+#define F_NEEDS_JIT_ENABLED			(1 << 2)
 
 /* need CAP_BPF, CAP_NET_ADMIN, CAP_PERFMON to load progs */
 #define ADMIN_CAPS (1ULL << CAP_NET_ADMIN |	\
 		    1ULL << CAP_PERFMON |	\
 		    1ULL << CAP_BPF)
 #define UNPRIV_SYSCTL "kernel/unprivileged_bpf_disabled"
 static bool unpriv_disabled = false;
+static bool jit_disabled;
 static int skips;
 static bool verbose = false;
 static int verif_log_level = 0;
@@ -1524,6 +1526,13 @@ static void do_test_single(struct bpf_test *test, bool unpriv,
 	__u32 pflags;
 	int i, err;
 
+	if ((test->flags & F_NEEDS_JIT_ENABLED) && jit_disabled) {
+		printf("SKIP (requires BPF JIT)");
+		skips++;
+		sched_yield();
+		return;
+	}
+
 	fd_prog = -1;
 	for (i = 0; i < MAX_NR_MAPS; i++)
 		map_fds[i] = -1;
@@ -1844,6 +1853,8 @@ int main(int argc, char **argv)
 		return EXIT_FAILURE;
 	}
 
+	jit_disabled = !is_jit_enabled();
+
 	/* Use libbpf 1.0 API mode */
 	libbpf_set_strict_mode(LIBBPF_STRICT_ALL);
 

tools/testing/selftests/bpf/verifier/bpf_loop_inline.c

@@ -57,6 +57,7 @@
 	.expected_insns = { PSEUDO_CALL_INSN() },
 	.unexpected_insns = { HELPER_CALL_INSN() },
 	.prog_type = BPF_PROG_TYPE_TRACEPOINT,
+	.flags = F_NEEDS_JIT_ENABLED,
 	.result = ACCEPT,
 	.runs = 0,
 	.func_info = { { 0, MAIN_TYPE }, { 12, CALLBACK_TYPE } },
@@ -90,6 +91,7 @@
 	.expected_insns = { HELPER_CALL_INSN() },
 	.unexpected_insns = { PSEUDO_CALL_INSN() },
 	.prog_type = BPF_PROG_TYPE_TRACEPOINT,
+	.flags = F_NEEDS_JIT_ENABLED,
 	.result = ACCEPT,
 	.runs = 0,
 	.func_info = { { 0, MAIN_TYPE }, { 16, CALLBACK_TYPE } },
@@ -127,6 +129,7 @@
 	.expected_insns = { HELPER_CALL_INSN() },
 	.unexpected_insns = { PSEUDO_CALL_INSN() },
 	.prog_type = BPF_PROG_TYPE_TRACEPOINT,
+	.flags = F_NEEDS_JIT_ENABLED,
 	.result = ACCEPT,
 	.runs = 0,
 	.func_info = {
@@ -165,6 +168,7 @@
 	.expected_insns = { PSEUDO_CALL_INSN() },
 	.unexpected_insns = { HELPER_CALL_INSN() },
 	.prog_type = BPF_PROG_TYPE_TRACEPOINT,
+	.flags = F_NEEDS_JIT_ENABLED,
 	.result = ACCEPT,
 	.runs = 0,
 	.func_info = {
@@ -235,6 +239,7 @@
 	},
 	.unexpected_insns = { HELPER_CALL_INSN() },
 	.prog_type = BPF_PROG_TYPE_TRACEPOINT,
+	.flags = F_NEEDS_JIT_ENABLED,
 	.result = ACCEPT,
 	.func_info = {
 		{ 0, MAIN_TYPE },
@@ -252,6 +257,7 @@
 	.unexpected_insns = { HELPER_CALL_INSN() },
 	.result = ACCEPT,
 	.prog_type = BPF_PROG_TYPE_TRACEPOINT,
+	.flags = F_NEEDS_JIT_ENABLED,
 	.func_info = { { 0, MAIN_TYPE }, { 16, CALLBACK_TYPE } },
 	.func_info_cnt = 2,
 	BTF_TYPES