[PATCH v4 bpf-next 3/3] veristat: guess and substitue underlying program type for freplace (EXT) progs

Andrii Nakryiko
2023-03-27T18:52:21Z

SEC("freplace") (i.e., BPF_PROG_TYPE_EXT) programs are not loadable as
is through veristat, as kernel expects actual program's FD during
BPF_PROG_LOAD time, which veristat has no way of knowing.

Unfortunately, freplace programs are a pretty important class of
programs, especially when dealing with XDP chaining solutions, which
rely on EXT programs.

So let's do our best and teach veristat to try to guess the original
program type, based on program's context argument type. And if guessing
process succeeds, we manually override freplace/EXT with guessed program
type using bpf_program__set_type() setter to increase chances of proper
BPF verification.

We rely on BTF and maintain a simple lookup table. This process is
obviously not 100% bulletproof, as valid program might not use context
and thus wouldn't have to specify correct type. Also, __sk_buff is very
ambiguous and is the context type across many different program types.
We pick BPF_PROG_TYPE_CGROUP_SKB for now, which seems to work fine in
practice so far. Similarly, some program types require specifying attach
type, and so we pick one out of possible few variants.

Best effort at its best. But this makes veristat even more widely
applicable.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
tools/testing/selftests/bpf/veristat.c | 121 ++++++++++++++++++++++++-
1 file changed, 117 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/bpf/veristat.c b/tools/testing/selftests/bpf/veristat.c
index 263df32fbda8..055df1abd7ca 100644
--- a/tools/testing/selftests/bpf/veristat.c
+++ b/tools/testing/selftests/bpf/veristat.c
@@ -15,6 +15,7 @@
#include <sys/sysinfo.h>
#include <sys/stat.h>
#include <bpf/libbpf.h>
+#include <bpf/btf.h>
#include <libelf.h>
#include <gelf.h>
#include <float.h>
@@ -778,7 +779,62 @@ static int parse_verif_log(char * const buf, size_t buf_sz, struct verif_stats *
return 0;
}

-static void fixup_obj(struct bpf_object *obj)
+static int guess_prog_type_by_ctx_name(const char *ctx_name,
+ enum bpf_prog_type *prog_type,
+ enum bpf_attach_type *attach_type)
+{
+ /* We need to guess program type based on its declared context type.
+ * This guess can't be perfect as many different program types might
+ * share the same context type. So we can only hope to reasonably
+ * well guess this and get lucky.
+ *
+ * Just in case, we support both UAPI-side type names and
+ * kernel-internal names.
+ */
+ static struct {
+ const char *uapi_name;
+ const char *kern_name;
+ enum bpf_prog_type prog_type;
+ enum bpf_attach_type attach_type;
+ } ctx_map[] = {
+ /* __sk_buff is most ambiguous, for now we assume cgroup_skb */
+ { "__sk_buff", "sk_buff", BPF_PROG_TYPE_CGROUP_SKB, BPF_CGROUP_INET_INGRESS },
+ { "bpf_sock", "sock", BPF_PROG_TYPE_CGROUP_SOCK, BPF_CGROUP_INET4_POST_BIND },
+ { "bpf_sock_addr", "bpf_sock_addr_kern", BPF_PROG_TYPE_CGROUP_SOCK_ADDR, BPF_CGROUP_INET4_BIND },
+ { "bpf_sock_ops", "bpf_sock_ops_kern", BPF_PROG_TYPE_SOCK_OPS, BPF_CGROUP_SOCK_OPS },
+ { "sk_msg_md", "sk_msg", BPF_PROG_TYPE_SK_MSG, BPF_SK_MSG_VERDICT },
+ { "bpf_cgroup_dev_ctx", "bpf_cgroup_dev_ctx", BPF_PROG_TYPE_CGROUP_DEVICE, BPF_CGROUP_DEVICE },
+ { "bpf_sysctl", "bpf_sysctl_kern", BPF_PROG_TYPE_CGROUP_SYSCTL, BPF_CGROUP_SYSCTL },
+ { "bpf_sockopt", "bpf_sockopt_kern", BPF_PROG_TYPE_CGROUP_SOCKOPT, BPF_CGROUP_SETSOCKOPT },
+ { "sk_reuseport_md", "sk_reuseport_kern", BPF_PROG_TYPE_SK_REUSEPORT, BPF_SK_REUSEPORT_SELECT_OR_MIGRATE },
+ { "bpf_sk_lookup", "bpf_sk_lookup_kern", BPF_PROG_TYPE_SK_LOOKUP, BPF_SK_LOOKUP },
+ { "xdp_md", "xdp_buff", BPF_PROG_TYPE_XDP, BPF_XDP },
+ /* tracing types with no expected attach type */
+ { "bpf_user_pt_regs_t", "pt_regs", BPF_PROG_TYPE_KPROBE },
+ { "bpf_perf_event_data", "bpf_perf_event_data_kern", BPF_PROG_TYPE_PERF_EVENT },
+ /* raw_tp programs use u64[] from kernel side, we don't want
+ * to match on that, probably; so NULL for kern-side type
+ */
+ { "bpf_raw_tracepoint_args", NULL, BPF_PROG_TYPE_RAW_TRACEPOINT },
+ };
+ int i;
+
+ if (!ctx_name)
+ return -EINVAL;
+
+ for (i = 0; i < ARRAY_SIZE(ctx_map); i++) {
+ if (strcmp(ctx_map[i].uapi_name, ctx_name) == 0 ||
+ (ctx_map[i].kern_name && strcmp(ctx_map[i].kern_name, ctx_name) == 0)) {
+ *prog_type = ctx_map[i].prog_type;
+ *attach_type = ctx_map[i].attach_type;
+ return 0;
+ }
+ }
+
+ return -ESRCH;
+}
+
+static void fixup_obj(struct bpf_object *obj, struct bpf_program *prog, const char *filename)
{
struct bpf_map *map;

@@ -798,18 +854,75 @@ static void fixup_obj(struct bpf_object *obj)
bpf_map__set_max_entries(map, 1);
}
}
+
+ /* SEC(freplace) programs can't be loaded with veristat as is,
+ * but we can try guessing their target program's expected type by
+ * looking at the type of program's first argument and substituting
+ * corresponding program type
+ */
+ if (bpf_program__type(prog) == BPF_PROG_TYPE_EXT) {
+ const struct btf *btf = bpf_object__btf(obj);
+ const char *prog_name = bpf_program__name(prog);
+ enum bpf_prog_type prog_type;
+ enum bpf_attach_type attach_type;
+ const struct btf_type *t;
+ const char *ctx_name;
+ int id;
+
+ if (!btf)
+ goto skip_freplace_fixup;
+
+ id = btf__find_by_name_kind(btf, prog_name, BTF_KIND_FUNC);
+ t = btf__type_by_id(btf, id);
+ t = btf__type_by_id(btf, t->type);
+ if (!btf_is_func_proto(t) || btf_vlen(t) != 1)
+ goto skip_freplace_fixup;
+
+ /* context argument is a pointer to a struct/typedef */
+ t = btf__type_by_id(btf, btf_params(t)[0].type);
+ while (t && btf_is_mod(t))
+ t = btf__type_by_id(btf, t->type);
+ if (!t || !btf_is_ptr(t))
+ goto skip_freplace_fixup;
+ t = btf__type_by_id(btf, t->type);
+ while (t && btf_is_mod(t))
+ t = btf__type_by_id(btf, t->type);
+ if (!t)
+ goto skip_freplace_fixup;
+
+ ctx_name = btf__name_by_offset(btf, t->name_off);
+
+ if (guess_prog_type_by_ctx_name(ctx_name, &prog_type, &attach_type) == 0) {
+ bpf_program__set_type(prog, prog_type);
+ bpf_program__set_expected_attach_type(prog, attach_type);
+
+ if (!env.quiet) {
+ printf("Using guessed program type '%s' for %s/%s...\n",
+ libbpf_bpf_prog_type_str(prog_type),
+ filename, prog_name);
+ }
+ } else {
+ if (!env.quiet) {
+ printf("Failed to guess program type for freplace program with context type name '%s' for %s/%s. Consider using canonical type names to help veristat...\n",
+ ctx_name, filename, prog_name);
+ }
+ }
+ }
+skip_freplace_fixup:
+ return;
}

static int process_prog(const char *filename, struct bpf_object *obj, struct bpf_program *prog)
{
const char *prog_name = bpf_program__name(prog);
+ const char *base_filename = basename(filename);
size_t buf_sz = sizeof(verif_log_buf);
char *buf = verif_log_buf;
struct verif_stats *stats;
int err = 0;
void *tmp;

- if (!should_process_file_prog(basename(filename), bpf_program__name(prog))) {
+ if (!should_process_file_prog(base_filename, bpf_program__name(prog))) {
env.progs_skipped++;
return 0;
}
@@ -835,12 +948,12 @@ static int process_prog(const char *filename, struct bpf_object *obj, struct bpf
verif_log_buf[0] = '\0';

/* increase chances of successful BPF object loading */
- fixup_obj(obj);
+ fixup_obj(obj, prog, base_filename);

err = bpf_object__load(obj);
env.progs_processed++;

- stats->file_name = strdup(basename(filename));
+ stats->file_name = strdup(base_filename);
stats->prog_name = strdup(bpf_program__name(prog));
stats->stats[VERDICT] = err == 0; /* 1 - success, 0 - failure */
parse_verif_log(buf, buf_sz, stats);
--
2.34.1