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authorAndrii Nakryiko <andrii@kernel.org>2024-01-17 19:31:39 -0800
committerAlexei Starovoitov <ast@kernel.org>2024-01-17 20:20:05 -0800
commit01b55f4f0cd6ad1a16eca6c43a3190005892ef91 (patch)
tree379519a1519a94a55e0e0948c405959f1eadc984
parent33772ff3b887eb2f426ed66bcb1808837a40669c (diff)
libbpf: feature-detect arg:ctx tag support in kernel
Add feature detector of kernel-side arg:ctx (__arg_ctx) tag support. If this is detected, libbpf will avoid doing any __arg_ctx-related BTF rewriting and checks in favor of letting kernel handle this completely. test_global_funcs/ctx_arg_rewrite subtest is adjusted to do the same feature detection (albeit in much simpler, though round-about and inefficient, way), and skip the tests. This is done to still be able to execute this test on older kernels (like in libbpf CI). Note, BPF token series ([0]) does a major refactor and code moving of libbpf-internal feature detection "framework", so to avoid unnecessary conflicts we keep newly added feature detection stand-alone with ad-hoc result caching. Once things settle, there will be a small follow up to re-integrate everything back and move code into its final place in newly-added (by BPF token series) features.c file. [0] https://patchwork.kernel.org/project/netdevbpf/list/?series=814209&state=* Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/r/20240118033143.3384355-2-andrii@kernel.org Signed-off-by: Alexei Starovoitov <ast@kernel.org>
-rw-r--r--tools/lib/bpf/libbpf.c67
-rw-r--r--tools/testing/selftests/bpf/prog_tests/test_global_funcs.c13
2 files changed, 80 insertions, 0 deletions
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index c5a42ac309fd..61db92189517 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -6757,6 +6757,69 @@ static int clone_func_btf_info(struct btf *btf, int orig_fn_id, struct bpf_progr
return fn_id;
}
+static int probe_kern_arg_ctx_tag(void)
+{
+ /* To minimize merge conflicts with BPF token series that refactors
+ * feature detection code a lot, we don't integrate
+ * probe_kern_arg_ctx_tag() into kernel_supports() feature-detection
+ * framework yet, doing our own caching internally.
+ * This will be cleaned up a bit later when bpf/bpf-next trees settle.
+ */
+ static int cached_result = -1;
+ static const char strs[] = "\0a\0b\0arg:ctx\0";
+ const __u32 types[] = {
+ /* [1] INT */
+ BTF_TYPE_INT_ENC(1 /* "a" */, BTF_INT_SIGNED, 0, 32, 4),
+ /* [2] PTR -> VOID */
+ BTF_TYPE_ENC(0, BTF_INFO_ENC(BTF_KIND_PTR, 0, 0), 0),
+ /* [3] FUNC_PROTO `int(void *a)` */
+ BTF_TYPE_ENC(0, BTF_INFO_ENC(BTF_KIND_FUNC_PROTO, 0, 1), 1),
+ BTF_PARAM_ENC(1 /* "a" */, 2),
+ /* [4] FUNC 'a' -> FUNC_PROTO (main prog) */
+ BTF_TYPE_ENC(1 /* "a" */, BTF_INFO_ENC(BTF_KIND_FUNC, 0, BTF_FUNC_GLOBAL), 3),
+ /* [5] FUNC_PROTO `int(void *b __arg_ctx)` */
+ BTF_TYPE_ENC(0, BTF_INFO_ENC(BTF_KIND_FUNC_PROTO, 0, 1), 1),
+ BTF_PARAM_ENC(3 /* "b" */, 2),
+ /* [6] FUNC 'b' -> FUNC_PROTO (subprog) */
+ BTF_TYPE_ENC(3 /* "b" */, BTF_INFO_ENC(BTF_KIND_FUNC, 0, BTF_FUNC_GLOBAL), 5),
+ /* [7] DECL_TAG 'arg:ctx' -> func 'b' arg 'b' */
+ BTF_TYPE_DECL_TAG_ENC(5 /* "arg:ctx" */, 6, 0),
+ };
+ const struct bpf_insn insns[] = {
+ /* main prog */
+ BPF_CALL_REL(+1),
+ BPF_EXIT_INSN(),
+ /* global subprog */
+ BPF_EMIT_CALL(BPF_FUNC_get_func_ip), /* needs PTR_TO_CTX */
+ BPF_EXIT_INSN(),
+ };
+ const struct bpf_func_info_min func_infos[] = {
+ { 0, 4 }, /* main prog -> FUNC 'a' */
+ { 2, 6 }, /* subprog -> FUNC 'b' */
+ };
+ LIBBPF_OPTS(bpf_prog_load_opts, opts);
+ int prog_fd, btf_fd, insn_cnt = ARRAY_SIZE(insns);
+
+ if (cached_result >= 0)
+ return cached_result;
+
+ btf_fd = libbpf__load_raw_btf((char *)types, sizeof(types), strs, sizeof(strs));
+ if (btf_fd < 0)
+ return 0;
+
+ opts.prog_btf_fd = btf_fd;
+ opts.func_info = &func_infos;
+ opts.func_info_cnt = ARRAY_SIZE(func_infos);
+ opts.func_info_rec_size = sizeof(func_infos[0]);
+
+ prog_fd = bpf_prog_load(BPF_PROG_TYPE_KPROBE, "det_arg_ctx",
+ "GPL", insns, insn_cnt, &opts);
+ close(btf_fd);
+
+ cached_result = probe_fd(prog_fd);
+ return cached_result;
+}
+
/* Check if main program or global subprog's function prototype has `arg:ctx`
* argument tags, and, if necessary, substitute correct type to match what BPF
* verifier would expect, taking into account specific program type. This
@@ -6780,6 +6843,10 @@ static int bpf_program_fixup_func_info(struct bpf_object *obj, struct bpf_progra
if (!obj->btf_ext || !prog->func_info)
return 0;
+ /* don't do any fix ups if kernel natively supports __arg_ctx */
+ if (probe_kern_arg_ctx_tag() > 0)
+ return 0;
+
/* some BPF program types just don't have named context structs, so
* this fallback mechanism doesn't work for them
*/
diff --git a/tools/testing/selftests/bpf/prog_tests/test_global_funcs.c b/tools/testing/selftests/bpf/prog_tests/test_global_funcs.c
index 67d4ef9e62b3..e905cbaf6b3d 100644
--- a/tools/testing/selftests/bpf/prog_tests/test_global_funcs.c
+++ b/tools/testing/selftests/bpf/prog_tests/test_global_funcs.c
@@ -47,6 +47,19 @@ static void subtest_ctx_arg_rewrite(void)
struct btf *btf = NULL;
__u32 info_len = sizeof(info);
int err, fd, i;
+ struct btf *kern_btf = NULL;
+
+ kern_btf = btf__load_vmlinux_btf();
+ if (!ASSERT_OK_PTR(kern_btf, "kern_btf_load"))
+ return;
+
+ /* simple detection of kernel native arg:ctx tag support */
+ if (btf__find_by_name_kind(kern_btf, "bpf_subprog_arg_info", BTF_KIND_STRUCT) > 0) {
+ test__skip();
+ btf__free(kern_btf);
+ return;
+ }
+ btf__free(kern_btf);
skel = test_global_func_ctx_args__open();
if (!ASSERT_OK_PTR(skel, "skel_open"))