[PATCH bpf-next v2 1/3] bpf: Add bpf_arch_supports_fsession()

[Leon Hwang <leon.hwang@linux.dev>]

fsession programs can currently be loaded on architectures that do not
implement fsession support, which leads to runtime errors instead of a
clean verifier rejection.

For example, running fsession selftests on arm64 before fsession support
is added results in:

test_fsession_basic:PASS:fsession_test__open_and_load 0 nsec
test_fsession_basic:PASS:fsession_attach 0 nsec
check_result:FAIL:test_run_opts err unexpected error: -14 (errno 14)

Introduce bpf_arch_supports_fsession() to explicitly gate fsession usage
based on architecture support. Architectures without fsession support
will now fail program load with -EOPNOTSUPP, allowing selftests to skip
cleanly instead of errors at runtime.

x86 declares fsession support, while the default implementation returns
false.

Fixes: 2d419c44658f ("bpf: add fsession support")
Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 arch/x86/net/bpf_jit_comp.c                   |  5 +++
 include/linux/filter.h                        |  1 +
 kernel/bpf/core.c                             |  5 +++
 kernel/bpf/verifier.c                         |  3 ++
 .../selftests/bpf/prog_tests/fsession_test.c  | 32 ++++++++++++++-----
 5 files changed, 38 insertions(+), 8 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 5a075e06cf45..070ba80e39d7 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -4112,3 +4112,8 @@ bool bpf_jit_supports_timed_may_goto(void)
 {
 	return true;
 }
+
+bool bpf_jit_supports_fsession(void)
+{
+	return true;
+}
diff --git a/include/linux/filter.h b/include/linux/filter.h
index fd54fed8f95f..4e1cb4f91f49 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -1167,6 +1167,7 @@ bool bpf_jit_supports_arena(void);
 bool bpf_jit_supports_insn(struct bpf_insn *insn, bool in_arena);
 bool bpf_jit_supports_private_stack(void);
 bool bpf_jit_supports_timed_may_goto(void);
+bool bpf_jit_supports_fsession(void);
 u64 bpf_arch_uaddress_limit(void);
 void arch_bpf_stack_walk(bool (*consume_fn)(void *cookie, u64 ip, u64 sp, u64 bp), void *cookie);
 u64 arch_bpf_timed_may_goto(void);
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index e0b8a8a5aaa9..3b1eb632bf7c 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -3142,6 +3142,11 @@ bool __weak bpf_jit_supports_insn(struct bpf_insn *insn, bool in_arena)
 	return false;
 }
 
+bool __weak bpf_jit_supports_fsession(void)
+{
+	return false;
+}
+
 u64 __weak bpf_arch_uaddress_limit(void)
 {
 #if defined(CONFIG_64BIT) && defined(CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index c2f2650db9fd..6f867ebf78d1 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -24872,6 +24872,9 @@ int bpf_check_attach_target(struct bpf_verifier_log *log,
 	case BPF_TRACE_FENTRY:
 	case BPF_TRACE_FEXIT:
 	case BPF_TRACE_FSESSION:
+		if (prog->expected_attach_type == BPF_TRACE_FSESSION &&
+		    !bpf_jit_supports_fsession())
+			return -EOPNOTSUPP;
 		if (!btf_type_is_func(t)) {
 			bpf_log(log, "attach_btf_id %u is not a function\n",
 				btf_id);
diff --git a/tools/testing/selftests/bpf/prog_tests/fsession_test.c b/tools/testing/selftests/bpf/prog_tests/fsession_test.c
index 0c4b428e1cee..a299aeb8cc2e 100644
--- a/tools/testing/selftests/bpf/prog_tests/fsession_test.c
+++ b/tools/testing/selftests/bpf/prog_tests/fsession_test.c
@@ -29,8 +29,16 @@ static void test_fsession_basic(void)
 	struct fsession_test *skel = NULL;
 	int err;
 
-	skel = fsession_test__open_and_load();
-	if (!ASSERT_OK_PTR(skel, "fsession_test__open_and_load"))
+	skel = fsession_test__open();
+	if (!ASSERT_OK_PTR(skel, "fsession_test__open"))
+		return;
+
+	err = fsession_test__load(skel);
+	if (err == -EOPNOTSUPP) {
+		test__skip();
+		goto cleanup;
+	}
+	if (!ASSERT_OK(err, "fsession_test__load"))
 		goto cleanup;
 
 	err = fsession_test__attach(skel);
@@ -47,8 +55,16 @@ static void test_fsession_reattach(void)
 	struct fsession_test *skel = NULL;
 	int err;
 
-	skel = fsession_test__open_and_load();
-	if (!ASSERT_OK_PTR(skel, "fsession_test__open_and_load"))
+	skel = fsession_test__open();
+	if (!ASSERT_OK_PTR(skel, "fsession_test__open"))
+		return;
+
+	err = fsession_test__load(skel);
+	if (err == -EOPNOTSUPP) {
+		test__skip();
+		goto cleanup;
+	}
+	if (!ASSERT_OK(err, "fsession_test__load"))
 		goto cleanup;
 
 	/* first attach */
@@ -94,6 +110,10 @@ static void test_fsession_cookie(void)
 	bpf_program__set_autoload(skel->progs.test6, false);
 
 	err = fsession_test__load(skel);
+	if (err == -EOPNOTSUPP) {
+		test__skip();
+		goto cleanup;
+	}
 	if (!ASSERT_OK(err, "fsession_test__load"))
 		goto cleanup;
 
@@ -111,10 +131,6 @@ static void test_fsession_cookie(void)
 
 void test_fsession_test(void)
 {
-#if !defined(__x86_64__)
-	test__skip();
-	return;
-#endif
 	if (test__start_subtest("fsession_test"))
 		test_fsession_basic();
 	if (test__start_subtest("fsession_reattach"))
-- 
2.52.0