Commit ac9f0605 authored by Kumar Kartikeya Dwivedi's avatar Kumar Kartikeya Dwivedi Committed by Alexei Starovoitov
Browse files

bpf: Introduce bpf_obj_drop 



Introduce bpf_obj_drop, which is the kfunc used to free allocated
objects (allocated using bpf_obj_new). Pairing with bpf_obj_new, it
implicitly destructs the fields part of object automatically without
user intervention.

Just like the previous patch, btf_struct_meta that is needed to free up
the special fields is passed as a hidden argument to the kfunc.

For the user, a convenience macro hides over the kernel side kfunc which
is named bpf_obj_drop_impl.

Continuing the previous example:

void prog(void) {
	struct foo *f;

	f = bpf_obj_new(typeof(*f));
	if (!f)
		return;
	bpf_obj_drop(f);
}

Signed-off-by: default avatarKumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20221118015614.2013203-15-memxor@gmail.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 958cf2e2

kernel/bpf/helpers.c

+11 −0
Original line number Diff line number Diff line
@@ -1770,6 +1770,16 @@ void *bpf_obj_new_impl(u64 local_type_id__k, void *meta__ign) 
	return p;

}



void bpf_obj_drop_impl(void *p__alloc, void *meta__ign)

{

	struct btf_struct_meta *meta = meta__ign;

	void *p = p__alloc;



	if (meta)

		bpf_obj_free_fields(meta->record, p);

	bpf_mem_free(&bpf_global_ma, p);

}



__diag_pop();



BTF_SET8_START(generic_btf_ids)
@@ -1777,6 +1787,7 @@ BTF_SET8_START(generic_btf_ids) 
BTF_ID_FLAGS(func, crash_kexec, KF_DESTRUCTIVE)

#endif

BTF_ID_FLAGS(func, bpf_obj_new_impl, KF_ACQUIRE | KF_RET_NULL)

BTF_ID_FLAGS(func, bpf_obj_drop_impl, KF_RELEASE)

BTF_SET8_END(generic_btf_ids)



static const struct btf_kfunc_id_set generic_kfunc_set = {

kernel/bpf/verifier.c

+55 −11
Original line number Diff line number Diff line
@@ -7879,6 +7879,10 @@ struct bpf_kfunc_call_arg_meta { 
		u64 value;

		bool found;

	} arg_constant;

	struct {

		struct btf *btf;

		u32 btf_id;

	} arg_obj_drop;

};



static bool is_kfunc_acquire(struct bpf_kfunc_call_arg_meta *meta)
@@ -7957,6 +7961,11 @@ static bool is_kfunc_arg_ignore(const struct btf *btf, const struct btf_param *a 
	return __kfunc_param_match_suffix(btf, arg, "__ign");

}



static bool is_kfunc_arg_alloc_obj(const struct btf *btf, const struct btf_param *arg)

{

	return __kfunc_param_match_suffix(btf, arg, "__alloc");

}



static bool is_kfunc_arg_scalar_with_name(const struct btf *btf,

					  const struct btf_param *arg,

					  const char *name)
@@ -8051,6 +8060,7 @@ static u32 *reg2btf_ids[__BPF_REG_TYPE_MAX] = { 


enum kfunc_ptr_arg_type {

	KF_ARG_PTR_TO_CTX,

	KF_ARG_PTR_TO_ALLOC_BTF_ID,  /* Allocated object */

	KF_ARG_PTR_TO_KPTR,	     /* PTR_TO_KPTR but type specific */

	KF_ARG_PTR_TO_DYNPTR,

	KF_ARG_PTR_TO_BTF_ID,	     /* Also covers reg2btf_ids conversions */
@@ -8058,6 +8068,20 @@ enum kfunc_ptr_arg_type { 
	KF_ARG_PTR_TO_MEM_SIZE,	     /* Size derived from next argument, skip it */

};



enum special_kfunc_type {

	KF_bpf_obj_new_impl,

	KF_bpf_obj_drop_impl,

};



BTF_SET_START(special_kfunc_set)

BTF_ID(func, bpf_obj_new_impl)

BTF_ID(func, bpf_obj_drop_impl)

BTF_SET_END(special_kfunc_set)



BTF_ID_LIST(special_kfunc_list)

BTF_ID(func, bpf_obj_new_impl)

BTF_ID(func, bpf_obj_drop_impl)



static enum kfunc_ptr_arg_type

get_kfunc_ptr_arg_type(struct bpf_verifier_env *env,

		       struct bpf_kfunc_call_arg_meta *meta,
@@ -8078,6 +8102,9 @@ get_kfunc_ptr_arg_type(struct bpf_verifier_env *env, 
	if (btf_get_prog_ctx_type(&env->log, meta->btf, t, resolve_prog_type(env->prog), argno))

		return KF_ARG_PTR_TO_CTX;



	if (is_kfunc_arg_alloc_obj(meta->btf, &args[argno]))

		return KF_ARG_PTR_TO_ALLOC_BTF_ID;



	if (is_kfunc_arg_kptr_get(meta, argno)) {

		if (!btf_type_is_ptr(ref_t)) {

			verbose(env, "arg#0 BTF type must be a double pointer for kptr_get kfunc\n");
@@ -8294,6 +8321,7 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_ 
			return kf_arg_type;



		switch (kf_arg_type) {

		case KF_ARG_PTR_TO_ALLOC_BTF_ID:

		case KF_ARG_PTR_TO_BTF_ID:

			if (!is_kfunc_trusted_args(meta))

				break;
@@ -8330,6 +8358,21 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_ 
				return -EINVAL;

			}

			break;

		case KF_ARG_PTR_TO_ALLOC_BTF_ID:

			if (reg->type != (PTR_TO_BTF_ID | MEM_ALLOC)) {

				verbose(env, "arg#%d expected pointer to allocated object\n", i);

				return -EINVAL;

			}

			if (!reg->ref_obj_id) {

				verbose(env, "allocated object must be referenced\n");

				return -EINVAL;

			}

			if (meta->btf == btf_vmlinux &&

			    meta->func_id == special_kfunc_list[KF_bpf_obj_drop_impl]) {

				meta->arg_obj_drop.btf = reg->btf;

				meta->arg_obj_drop.btf_id = reg->btf_id;

			}

			break;

		case KF_ARG_PTR_TO_KPTR:

			if (reg->type != PTR_TO_MAP_VALUE) {

				verbose(env, "arg#0 expected pointer to map value\n");
@@ -8400,17 +8443,6 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_ 
	return 0;

}



enum special_kfunc_type {

	KF_bpf_obj_new_impl,

};



BTF_SET_START(special_kfunc_set)

BTF_ID(func, bpf_obj_new_impl)

BTF_SET_END(special_kfunc_set)



BTF_ID_LIST(special_kfunc_list)

BTF_ID(func, bpf_obj_new_impl)



static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,

			    int *insn_idx_p)

{
@@ -8532,6 +8564,10 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn, 
				env->insn_aux_data[insn_idx].obj_new_size = ret_t->size;

				env->insn_aux_data[insn_idx].kptr_struct_meta =

					btf_find_struct_meta(ret_btf, ret_btf_id);

			} else if (meta.func_id == special_kfunc_list[KF_bpf_obj_drop_impl]) {

				env->insn_aux_data[insn_idx].kptr_struct_meta =

					btf_find_struct_meta(meta.arg_obj_drop.btf,

							     meta.arg_obj_drop.btf_id);

			} else {

				verbose(env, "kernel function %s unhandled dynamic return type\n",

					meta.func_name);
@@ -14768,6 +14804,14 @@ static int fixup_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn, 
		insn_buf[2] = addr[1];

		insn_buf[3] = *insn;

		*cnt = 4;

	} else if (desc->func_id == special_kfunc_list[KF_bpf_obj_drop_impl]) {

		struct btf_struct_meta *kptr_struct_meta = env->insn_aux_data[insn_idx].kptr_struct_meta;

		struct bpf_insn addr[2] = { BPF_LD_IMM64(BPF_REG_2, (long)kptr_struct_meta) };



		insn_buf[0] = addr[0];

		insn_buf[1] = addr[1];

		insn_buf[2] = *insn;

		*cnt = 3;

	}

	return 0;

}

tools/testing/selftests/bpf/bpf_experimental.h

+13 −0
Original line number Diff line number Diff line
@@ -22,4 +22,17 @@ extern void *bpf_obj_new_impl(__u64 local_type_id, void *meta) __ksym; 
/* Convenience macro to wrap over bpf_obj_new_impl */

#define bpf_obj_new(type) ((type *)bpf_obj_new_impl(bpf_core_type_id_local(type), NULL))



/* Description

 *	Free an allocated object. All fields of the object that require

 *	destruction will be destructed before the storage is freed.

 *

 *	The 'meta' parameter is a hidden argument that is ignored.

 * Returns

 *	Void.

 */

extern void bpf_obj_drop_impl(void *kptr, void *meta) __ksym;



/* Convenience macro to wrap over bpf_obj_drop_impl */

#define bpf_obj_drop(kptr) bpf_obj_drop_impl(kptr, NULL)



#endif