Skip to content

Commit

Permalink
bpf: Introduce bpf_obj_drop
Browse files Browse the repository at this point in the history 
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: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20221118015614.2013203-15-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
  • Loading branch information
@kkdwivedi
kkdwivedi authored and Alexei Starovoitov committed Nov 18, 2022
1 parent 958cf2e commit ac9f060
Show file tree
Hide file tree
Showing 3 changed files with 79 additions and 11 deletions.
11 changes: 11 additions & 0 deletions kernel/bpf/helpers.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1770,13 +1770,24 @@ 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)
#ifdef CONFIG_KEXEC_CORE
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 = {
Expand Down
66 changes: 55 additions & 11 deletions kernel/bpf/verifier.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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)
Expand Down Expand Up @@ -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)
Expand Down Expand Up @@ -8051,13 +8060,28 @@ 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 */
KF_ARG_PTR_TO_MEM,
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,
Expand All @@ -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");
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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");
Expand Down Expand Up @@ -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)
{
Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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;
}
Expand Down
13 changes: 13 additions & 0 deletions tools/testing/selftests/bpf/bpf_experimental.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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

0 comments on commit ac9f060

Please sign in to comment.