Merge branch 'support-passing-bpf-iterator-to-kfuncs'

Andrii Nakryiko says:

====================
Support passing BPF iterator to kfuncs

Add support for passing BPF iterator state to any kfunc. Such kfunc has to
declare such argument with valid `struct bpf_iter_<type> *` type and should
use "__iter" suffix in argument name, following the established suffix-based
convention. We add a simple test/demo iterator getter in bpf_testmod.
====================

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

include/linux/btf.h

···
 int get_kern_ctx_btf_id(struct bpf_verifier_log *log, enum bpf_prog_type prog_type);
 bool btf_types_are_same(const struct btf *btf1, u32 id1,
 			const struct btf *btf2, u32 id2);
+int btf_check_iter_arg(struct btf *btf, const struct btf_type *func, int arg_idx);
 #else
 static inline const struct btf_type *btf_type_by_id(const struct btf *btf,
 						    u32 type_id)
···
 				      const struct btf *btf2, u32 id2)
 {
 	return false;
+}
+static inline int btf_check_iter_arg(struct btf *btf, const struct btf_type *func, int arg_idx)
+{
+	return -EOPNOTSUPP;
 }
 #endif
 

kernel/bpf/btf.c

···
 BTF_TRACING_TYPE_xxx
 #undef BTF_TRACING_TYPE
 
+/* Validate well-formedness of iter argument type.
+ * On success, return positive BTF ID of iter state's STRUCT type.
+ * On error, negative error is returned.
+ */
+int btf_check_iter_arg(struct btf *btf, const struct btf_type *func, int arg_idx)
+{
+	const struct btf_param *arg;
+	const struct btf_type *t;
+	const char *name;
+	int btf_id;
+
+	if (btf_type_vlen(func) <= arg_idx)
+		return -EINVAL;
+
+	arg = &btf_params(func)[arg_idx];
+	t = btf_type_skip_modifiers(btf, arg->type, NULL);
+	if (!t || !btf_type_is_ptr(t))
+		return -EINVAL;
+	t = btf_type_skip_modifiers(btf, t->type, &btf_id);
+	if (!t || !__btf_type_is_struct(t))
+		return -EINVAL;
+
+	name = btf_name_by_offset(btf, t->name_off);
+	if (!name || strncmp(name, ITER_PREFIX, sizeof(ITER_PREFIX) - 1))
+		return -EINVAL;
+
+	return btf_id;
+}
+
 static int btf_check_iter_kfuncs(struct btf *btf, const char *func_name,
 				 const struct btf_type *func, u32 func_flags)
 {
 	u32 flags = func_flags & (KF_ITER_NEW | KF_ITER_NEXT | KF_ITER_DESTROY);
-	const char *name, *sfx, *iter_name;
-	const struct btf_param *arg;
+	const char *sfx, *iter_name;
 	const struct btf_type *t;
 	char exp_name[128];
 	u32 nr_args;
+	int btf_id;
 
 	/* exactly one of KF_ITER_{NEW,NEXT,DESTROY} can be set */
 	if (!flags || (flags & (flags - 1)))
···
 	if (nr_args < 1)
 		return -EINVAL;
 
-	arg = &btf_params(func)[0];
-	t = btf_type_skip_modifiers(btf, arg->type, NULL);
-	if (!t || !btf_type_is_ptr(t))
-		return -EINVAL;
-	t = btf_type_skip_modifiers(btf, t->type, NULL);
-	if (!t || !__btf_type_is_struct(t))
-		return -EINVAL;
-
-	name = btf_name_by_offset(btf, t->name_off);
-	if (!name || strncmp(name, ITER_PREFIX, sizeof(ITER_PREFIX) - 1))
-		return -EINVAL;
+	btf_id = btf_check_iter_arg(btf, func, 0);
+	if (btf_id < 0)
+		return btf_id;
 
 	/* sizeof(struct bpf_iter_<type>) should be a multiple of 8 to
 	 * fit nicely in stack slots
 	 */
+	t = btf_type_by_id(btf, btf_id);
 	if (t->size == 0 || (t->size % 8))
 		return -EINVAL;
 
 	/* validate bpf_iter_<type>_{new,next,destroy}(struct bpf_iter_<type> *)
 	 * naming pattern
 	 */
-	iter_name = name + sizeof(ITER_PREFIX) - 1;
+	iter_name = btf_name_by_offset(btf, t->name_off) + sizeof(ITER_PREFIX) - 1;
 	if (flags & KF_ITER_NEW)
 		sfx = "new";
 	else if (flags & KF_ITER_NEXT)

kernel/bpf/verifier.c

···
 	return meta->kfunc_flags & KF_ITER_DESTROY;
 }
 
-static bool is_kfunc_arg_iter(struct bpf_kfunc_call_arg_meta *meta, int arg)
+static bool is_kfunc_arg_iter(struct bpf_kfunc_call_arg_meta *meta, int arg_idx,
+			      const struct btf_param *arg)
 {
 	/* btf_check_iter_kfuncs() guarantees that first argument of any iter
 	 * kfunc is iter state pointer
 	 */
-	return arg == 0 && is_iter_kfunc(meta);
+	if (is_iter_kfunc(meta))
+		return arg_idx == 0;
+
+	/* iter passed as an argument to a generic kfunc */
+	return btf_param_match_suffix(meta->btf, arg, "__iter");
 }
 
 static int process_iter_arg(struct bpf_verifier_env *env, int regno, int insn_idx,
···
 {
 	struct bpf_reg_state *regs = cur_regs(env), *reg = &regs[regno];
 	const struct btf_type *t;
-	const struct btf_param *arg;
-	int spi, err, i, nr_slots;
-	u32 btf_id;
+	int spi, err, i, nr_slots, btf_id;
 
-	/* btf_check_iter_kfuncs() ensures we don't need to validate anything here */
-	arg = &btf_params(meta->func_proto)[0];
-	t = btf_type_skip_modifiers(meta->btf, arg->type, NULL);	/* PTR */
-	t = btf_type_skip_modifiers(meta->btf, t->type, &btf_id);	/* STRUCT */
+	/* For iter_{new,next,destroy} functions, btf_check_iter_kfuncs()
+	 * ensures struct convention, so we wouldn't need to do any BTF
+	 * validation here. But given iter state can be passed as a parameter
+	 * to any kfunc, if arg has "__iter" suffix, we need to be a bit more
+	 * conservative here.
+	 */
+	btf_id = btf_check_iter_arg(meta->btf, meta->func_proto, regno - 1);
+	if (btf_id < 0) {
+		verbose(env, "expected valid iter pointer as arg #%d\n", regno);
+		return -EINVAL;
+	}
+	t = btf_type_by_id(meta->btf, btf_id);
 	nr_slots = t->size / BPF_REG_SIZE;
 
 	if (is_iter_new_kfunc(meta)) {
···
 		if (err)
 			return err;
 	} else {
-		/* iter_next() or iter_destroy() expect initialized iter state*/
+		/* iter_next() or iter_destroy(), as well as any kfunc
+		 * accepting iter argument, expect initialized iter state
+		 */
 		err = is_iter_reg_valid_init(env, reg, meta->btf, btf_id, nr_slots);
 		switch (err) {
 		case 0:
···
 	if (is_kfunc_arg_dynptr(meta->btf, &args[argno]))
 		return KF_ARG_PTR_TO_DYNPTR;
 
-	if (is_kfunc_arg_iter(meta, argno))
+	if (is_kfunc_arg_iter(meta, argno, &args[argno]))
 		return KF_ARG_PTR_TO_ITER;
 
 	if (is_kfunc_arg_list_head(meta->btf, &args[argno]))

tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c

···
 
 __bpf_kfunc int bpf_iter_testmod_seq_new(struct bpf_iter_testmod_seq *it, s64 value, int cnt)
 {
-	if (cnt < 0) {
-		it->cnt = 0;
+	it->cnt = cnt;
+
+	if (cnt < 0)
 		return -EINVAL;
-	}
 
 	it->value = value;
-	it->cnt = cnt;
 
 	return 0;
 }
···
 	it->cnt--;
 
 	return &it->value;
+}
+
+__bpf_kfunc s64 bpf_iter_testmod_seq_value(int val, struct bpf_iter_testmod_seq* it__iter)
+{
+	if (it__iter->cnt < 0)
+		return 0;
+
+	return val + it__iter->value;
 }
 
 __bpf_kfunc void bpf_iter_testmod_seq_destroy(struct bpf_iter_testmod_seq *it)
···
 BTF_ID_FLAGS(func, bpf_iter_testmod_seq_new, KF_ITER_NEW)
 BTF_ID_FLAGS(func, bpf_iter_testmod_seq_next, KF_ITER_NEXT | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_iter_testmod_seq_destroy, KF_ITER_DESTROY)
+BTF_ID_FLAGS(func, bpf_iter_testmod_seq_value)
 BTF_ID_FLAGS(func, bpf_kfunc_common_test)
 BTF_ID_FLAGS(func, bpf_kfunc_dynptr_test)
 BTF_ID_FLAGS(func, bpf_testmod_ctx_create, KF_ACQUIRE | KF_RET_NULL)

tools/testing/selftests/bpf/progs/iters_testmod_seq.c

···
 
 extern int bpf_iter_testmod_seq_new(struct bpf_iter_testmod_seq *it, s64 value, int cnt) __ksym;
 extern s64 *bpf_iter_testmod_seq_next(struct bpf_iter_testmod_seq *it) __ksym;
+extern s64 bpf_iter_testmod_seq_value(int blah, struct bpf_iter_testmod_seq *it) __ksym;
 extern void bpf_iter_testmod_seq_destroy(struct bpf_iter_testmod_seq *it) __ksym;
 
 const volatile __s64 exp_empty = 0 + 1;
···
 	res_truncated = sum;
 
 	return 0;
+}
+
+SEC("?raw_tp")
+__failure
+__msg("expected an initialized iter_testmod_seq as arg #2")
+int testmod_seq_getter_before_bad(const void *ctx)
+{
+	struct bpf_iter_testmod_seq it;
+
+	return bpf_iter_testmod_seq_value(0, &it);
+}
+
+SEC("?raw_tp")
+__failure
+__msg("expected an initialized iter_testmod_seq as arg #2")
+int testmod_seq_getter_after_bad(const void *ctx)
+{
+	struct bpf_iter_testmod_seq it;
+	s64 sum = 0, *v;
+
+	bpf_iter_testmod_seq_new(&it, 100, 100);
+
+	while ((v = bpf_iter_testmod_seq_next(&it))) {
+		sum += *v;
+	}
+
+	bpf_iter_testmod_seq_destroy(&it);
+
+	return sum + bpf_iter_testmod_seq_value(0, &it);
+}
+
+SEC("?socket")
+__success __retval(1000000)
+int testmod_seq_getter_good(const void *ctx)
+{
+	struct bpf_iter_testmod_seq it;
+	s64 sum = 0, *v;
+
+	bpf_iter_testmod_seq_new(&it, 100, 100);
+
+	while ((v = bpf_iter_testmod_seq_next(&it))) {
+		sum += *v;
+	}
+
+	sum *= bpf_iter_testmod_seq_value(0, &it);
+
+	bpf_iter_testmod_seq_destroy(&it);
+
+	return sum;
 }
 
 char _license[] SEC("license") = "GPL";