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bpf: Introduce bpf_obj_drop

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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>
This commit is contained in:
Kumar Kartikeya Dwivedi 2022-11-18 07:26:04 +05:30 committed by Alexei Starovoitov
parent 958cf2e273
commit ac9f06050a
3 changed files with 79 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
kernel/bpf/helpers.c
View File

@ -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 = {

66
kernel/bpf/verifier.c
View File

@ -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;
}

13
tools/testing/selftests/bpf/bpf_experimental.h
View File

@ -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