[v2,bpf-next] selftests/bpf: detect testing prog flags support

Commit Message

Andrii Nakryiko Jan. 9, 2024, 11:17 p.m. UTC

Various tests specify extra testing prog_flags when loading BPF
programs, like BPF_F_TEST_RND_HI32, and more recently also
BPF_F_TEST_REG_INVARIANTS. While BPF_F_TEST_RND_HI32 is old enough to
not cause much problem on older kernels, BPF_F_TEST_REG_INVARIANTS is
very fresh and unconditionally specifying it causes selftests to fail on
even slightly outdated kernels.

This breaks libbpf CI test against 4.9 and 5.15 kernels, it can break
some local development (done outside of VM), etc.

To prevent this, and guard against similar problems in the future, do
runtime detection of supported "testing flags", and only provide those
that host kernel recognizes.

Acked-by: Song Liu <[e-mail]>
Acked-by: Jiri Olsa <[e-mail]>
Signed-off-by: Andrii Nakryiko <[e-mail]>
---
 .../bpf/prog_tests/bpf_verif_scale.c          |  2 +-
 .../selftests/bpf/prog_tests/reg_bounds.c     |  2 +-
 tools/testing/selftests/bpf/test_loader.c     |  2 +-
 tools/testing/selftests/bpf/test_sock_addr.c  |  3 +-
 tools/testing/selftests/bpf/test_verifier.c   |  2 +-
 tools/testing/selftests/bpf/testing_helpers.c | 32 +++++++++++++++++--
 tools/testing/selftests/bpf/testing_helpers.h |  2 ++
 7 files changed, 38 insertions(+), 7 deletions(-)

Comments

[e-mail] Jan. 12, 2024, 2:40 a.m. UTC | #1

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <[e-mail]>:

On Tue,  9 Jan 2024 15:17:38 -0800 you wrote:
> Various tests specify extra testing prog_flags when loading BPF
> programs, like BPF_F_TEST_RND_HI32, and more recently also
> BPF_F_TEST_REG_INVARIANTS. While BPF_F_TEST_RND_HI32 is old enough to
> not cause much problem on older kernels, BPF_F_TEST_REG_INVARIANTS is
> very fresh and unconditionally specifying it causes selftests to fail on
> even slightly outdated kernels.
> 
> [...]

Here is the summary with links:
  - [v2,bpf-next] selftests/bpf: detect testing prog flags support
    https://git.kernel.org/bpf/bpf-next/c/ed145390380d

You are awesome, thank you!

Patch

diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_verif_scale.c b/tools/testing/selftests/bpf/prog_tests/bpf_verif_scale.c
index e770912fc1d2..4c6ada5b270b 100644
--- a/tools/testing/selftests/bpf/prog_tests/bpf_verif_scale.c
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_verif_scale.c
@@ -35,7 +35,7 @@  static int check_load(const char *file, enum bpf_prog_type type)
 	}
 
 	bpf_program__set_type(prog, type);
-	bpf_program__set_flags(prog, BPF_F_TEST_RND_HI32 | BPF_F_TEST_REG_INVARIANTS);
+	bpf_program__set_flags(prog, testing_prog_flags());
 	bpf_program__set_log_level(prog, 4 | extra_prog_load_log_flags);
 
 	err = bpf_object__load(obj);
diff --git a/tools/testing/selftests/bpf/prog_tests/reg_bounds.c b/tools/testing/selftests/bpf/prog_tests/reg_bounds.c
index 820d0bcfc474..eb74363f9f70 100644
--- a/tools/testing/selftests/bpf/prog_tests/reg_bounds.c
+++ b/tools/testing/selftests/bpf/prog_tests/reg_bounds.c
@@ -840,7 +840,7 @@  static int load_range_cmp_prog(struct range x, struct range y, enum op op,
 		.log_level = 2,
 		.log_buf = log_buf,
 		.log_size = log_sz,
-		.prog_flags = BPF_F_TEST_REG_INVARIANTS,
+		.prog_flags = testing_prog_flags(),
 	);
 
 	/* ; skip exit block below
diff --git a/tools/testing/selftests/bpf/test_loader.c b/tools/testing/selftests/bpf/test_loader.c
index f01391021218..2c954f40f815 100644
--- a/tools/testing/selftests/bpf/test_loader.c
+++ b/tools/testing/selftests/bpf/test_loader.c
@@ -181,7 +181,7 @@  static int parse_test_spec(struct test_loader *tester,
 	memset(spec, 0, sizeof(*spec));
 
 	spec->prog_name = bpf_program__name(prog);
-	spec->prog_flags = BPF_F_TEST_REG_INVARIANTS; /* by default be strict */
+	spec->prog_flags = testing_prog_flags();
 
 	btf = bpf_object__btf(obj);
 	if (!btf) {
diff --git a/tools/testing/selftests/bpf/test_sock_addr.c b/tools/testing/selftests/bpf/test_sock_addr.c
index b0068a9d2cfe..80c42583f597 100644
--- a/tools/testing/selftests/bpf/test_sock_addr.c
+++ b/tools/testing/selftests/bpf/test_sock_addr.c
@@ -19,6 +19,7 @@ 
 #include <bpf/libbpf.h>
 
 #include "cgroup_helpers.h"
+#include "testing_helpers.h"
 #include "bpf_util.h"
 
 #ifndef ENOTSUPP
@@ -679,7 +680,7 @@  static int load_path(const struct sock_addr_test *test, const char *path)
 
 	bpf_program__set_type(prog, BPF_PROG_TYPE_CGROUP_SOCK_ADDR);
 	bpf_program__set_expected_attach_type(prog, test->expected_attach_type);
-	bpf_program__set_flags(prog, BPF_F_TEST_RND_HI32 | BPF_F_TEST_REG_INVARIANTS);
+	bpf_program__set_flags(prog, testing_prog_flags());
 
 	err = bpf_object__load(obj);
 	if (err) {
diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
index f36e41435be7..50fdc1100a4b 100644
--- a/tools/testing/selftests/bpf/test_verifier.c
+++ b/tools/testing/selftests/bpf/test_verifier.c
@@ -1588,7 +1588,7 @@  static void do_test_single(struct bpf_test *test, bool unpriv,
 	if (fixup_skips != skips)
 		return;
 
-	pflags = BPF_F_TEST_RND_HI32 | BPF_F_TEST_REG_INVARIANTS;
+	pflags = testing_prog_flags();
 	if (test->flags & F_LOAD_WITH_STRICT_ALIGNMENT)
 		pflags |= BPF_F_STRICT_ALIGNMENT;
 	if (test->flags & F_NEEDS_EFFICIENT_UNALIGNED_ACCESS)
diff --git a/tools/testing/selftests/bpf/testing_helpers.c b/tools/testing/selftests/bpf/testing_helpers.c
index d2458c1b1671..ba9311fd0510 100644
--- a/tools/testing/selftests/bpf/testing_helpers.c
+++ b/tools/testing/selftests/bpf/testing_helpers.c
@@ -252,6 +252,34 @@  __u32 link_info_prog_id(const struct bpf_link *link, struct bpf_link_info *info)
 
 int extra_prog_load_log_flags = 0;
 
+int testing_prog_flags(void)
+{
+	static int cached_flags = -1;
+	static int prog_flags[] = { BPF_F_TEST_RND_HI32, BPF_F_TEST_REG_INVARIANTS };
+	static struct bpf_insn insns[] = {
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_EXIT_INSN(),
+	};
+	int insn_cnt = ARRAY_SIZE(insns), i, fd, flags = 0;
+	LIBBPF_OPTS(bpf_prog_load_opts, opts);
+
+	if (cached_flags >= 0)
+		return cached_flags;
+
+	for (i = 0; i < ARRAY_SIZE(prog_flags); i++) {
+		opts.prog_flags = prog_flags[i];
+		fd = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, "flag-test", "GPL",
+				   insns, insn_cnt, &opts);
+		if (fd >= 0) {
+			flags |= prog_flags[i];
+			close(fd);
+		}
+	}
+
+	cached_flags = flags;
+	return cached_flags;
+}
+
 int bpf_prog_test_load(const char *file, enum bpf_prog_type type,
 		       struct bpf_object **pobj, int *prog_fd)
 {
@@ -276,7 +304,7 @@  int bpf_prog_test_load(const char *file, enum bpf_prog_type type,
 	if (type != BPF_PROG_TYPE_UNSPEC && bpf_program__type(prog) != type)
 		bpf_program__set_type(prog, type);
 
-	flags = bpf_program__flags(prog) | BPF_F_TEST_RND_HI32 | BPF_F_TEST_REG_INVARIANTS;
+	flags = bpf_program__flags(prog) | testing_prog_flags();
 	bpf_program__set_flags(prog, flags);
 
 	err = bpf_object__load(obj);
@@ -299,7 +327,7 @@  int bpf_test_load_program(enum bpf_prog_type type, const struct bpf_insn *insns,
 {
 	LIBBPF_OPTS(bpf_prog_load_opts, opts,
 		.kern_version = kern_version,
-		.prog_flags = BPF_F_TEST_RND_HI32 | BPF_F_TEST_REG_INVARIANTS,
+		.prog_flags = testing_prog_flags(),
 		.log_level = extra_prog_load_log_flags,
 		.log_buf = log_buf,
 		.log_size = log_buf_sz,
diff --git a/tools/testing/selftests/bpf/testing_helpers.h b/tools/testing/selftests/bpf/testing_helpers.h
index 35284faff4f2..1caa16f5096c 100644
--- a/tools/testing/selftests/bpf/testing_helpers.h
+++ b/tools/testing/selftests/bpf/testing_helpers.h
@@ -46,4 +46,6 @@  static inline __u64 get_time_ns(void)
 	return (u64)t.tv_sec * 1000000000 + t.tv_nsec;
 }
 
+int testing_prog_flags(void);
+
 #endif /* __TESTING_HELPERS_H */