Commit 36d8bdf7 authored by Yonghong Song's avatar Yonghong Song Committed by Alexei Starovoitov
Browse files

bpf: Add alloc/xchg/direct_access support for local percpu kptr 



Add two new kfunc's, bpf_percpu_obj_new_impl() and
bpf_percpu_obj_drop_impl(), to allocate a percpu obj.
Two functions are very similar to bpf_obj_new_impl()
and bpf_obj_drop_impl(). The major difference is related
to percpu handling.

    bpf_rcu_read_lock()
    struct val_t __percpu_kptr *v = map_val->percpu_data;
    ...
    bpf_rcu_read_unlock()

For a percpu data map_val like above 'v', the reg->type
is set as
	PTR_TO_BTF_ID | MEM_PERCPU | MEM_RCU
if inside rcu critical section.

MEM_RCU marking here is similar to NON_OWN_REF as 'v'
is not a owning reference. But NON_OWN_REF is
trusted and typically inside the spinlock while
MEM_RCU is under rcu read lock. RCU is preferred here
since percpu data structures mean potential concurrent
access into its contents.

Also, bpf_percpu_obj_new_impl() is restricted such that
no pointers or special fields are allowed. Therefore,
the bpf_list_head and bpf_rb_root will not be supported
in this patch set to avoid potential memory leak issue
due to racing between bpf_obj_free_fields() and another
bpf_kptr_xchg() moving an allocated object to
bpf_list_head and bpf_rb_root.

Signed-off-by: default avatarYonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20230827152744.1996739-1-yonghong.song@linux.dev


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 55db92f4

kernel/bpf/helpers.c

+16 −0
Original line number Diff line number Diff line
@@ -1902,6 +1902,14 @@ __bpf_kfunc void *bpf_obj_new_impl(u64 local_type_id__k, void *meta__ign) 
	return p;

}



__bpf_kfunc void *bpf_percpu_obj_new_impl(u64 local_type_id__k, void *meta__ign)

{

	u64 size = local_type_id__k;



	/* The verifier has ensured that meta__ign must be NULL */

	return bpf_mem_alloc(&bpf_global_percpu_ma, size);

}



/* Must be called under migrate_disable(), as required by bpf_mem_free */

void __bpf_obj_drop_impl(void *p, const struct btf_record *rec)

{
@@ -1930,6 +1938,12 @@ __bpf_kfunc void bpf_obj_drop_impl(void *p__alloc, void *meta__ign) 
	__bpf_obj_drop_impl(p, meta ? meta->record : NULL);

}



__bpf_kfunc void bpf_percpu_obj_drop_impl(void *p__alloc, void *meta__ign)

{

	/* The verifier has ensured that meta__ign must be NULL */

	bpf_mem_free_rcu(&bpf_global_percpu_ma, p__alloc);

}



__bpf_kfunc void *bpf_refcount_acquire_impl(void *p__refcounted_kptr, void *meta__ign)

{

	struct btf_struct_meta *meta = meta__ign;
@@ -2442,7 +2456,9 @@ 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_percpu_obj_new_impl, KF_ACQUIRE | KF_RET_NULL)

BTF_ID_FLAGS(func, bpf_obj_drop_impl, KF_RELEASE)

BTF_ID_FLAGS(func, bpf_percpu_obj_drop_impl, KF_RELEASE)

BTF_ID_FLAGS(func, bpf_refcount_acquire_impl, KF_ACQUIRE | KF_RET_NULL)

BTF_ID_FLAGS(func, bpf_list_push_front_impl)

BTF_ID_FLAGS(func, bpf_list_push_back_impl)

kernel/bpf/verifier.c

+90 −22
Original line number Diff line number Diff line
@@ -304,7 +304,7 @@ struct bpf_kfunc_call_arg_meta { 
	/* arg_{btf,btf_id,owning_ref} are used by kfunc-specific handling,

	 * generally to pass info about user-defined local kptr types to later

	 * verification logic

	 *   bpf_obj_drop

	 *   bpf_obj_drop/bpf_percpu_obj_drop

	 *     Record the local kptr type to be drop'd

	 *   bpf_refcount_acquire (via KF_ARG_PTR_TO_REFCOUNTED_KPTR arg type)

	 *     Record the local kptr type to be refcount_incr'd and use
@@ -5001,6 +5001,8 @@ static int map_kptr_match_type(struct bpf_verifier_env *env, 
			perm_flags |= PTR_UNTRUSTED;

	} else {

		perm_flags = PTR_MAYBE_NULL | MEM_ALLOC;

		if (kptr_field->type == BPF_KPTR_PERCPU)

			perm_flags |= MEM_PERCPU;

	}









	if (base_type(reg->type) != PTR_TO_BTF_ID || (type_flag(reg->type) & ~perm_flags))








@@ -5044,7 +5046,7 @@ static int map_kptr_match_type(struct bpf_verifier_env *env,







	 */









	if (!btf_struct_ids_match(&env->log, reg->btf, reg->btf_id, reg->off,









				  kptr_field->kptr.btf, kptr_field->kptr.btf_id,









				  kptr_field->type == BPF_KPTR_REF))









				  kptr_field->type != BPF_KPTR_UNREF))









		goto bad_type;









	return 0;









bad_type:








@@ -5088,7 +5090,18 @@ static bool rcu_safe_kptr(const struct btf_field *field)







{









	const struct btf_field_kptr *kptr = &field->kptr;

















	return field->type == BPF_KPTR_REF && rcu_protected_object(kptr->btf, kptr->btf_id);









	return field->type == BPF_KPTR_PERCPU ||









	       (field->type == BPF_KPTR_REF && rcu_protected_object(kptr->btf, kptr->btf_id));









}

















static u32 btf_ld_kptr_type(struct bpf_verifier_env *env, struct btf_field *kptr_field)









{









	if (rcu_safe_kptr(kptr_field) && in_rcu_cs(env)) {









		if (kptr_field->type != BPF_KPTR_PERCPU)









			return PTR_MAYBE_NULL | MEM_RCU;









		return PTR_MAYBE_NULL | MEM_RCU | MEM_PERCPU;









	}









	return PTR_MAYBE_NULL | PTR_UNTRUSTED;









}

















static int check_map_kptr_access(struct bpf_verifier_env *env, u32 regno,








@@ -5114,7 +5127,8 @@ static int check_map_kptr_access(struct bpf_verifier_env *env, u32 regno,







	/* We only allow loading referenced kptr, since it will be marked as









	 * untrusted, similar to unreferenced kptr.









	 */









	if (class != BPF_LDX && kptr_field->type == BPF_KPTR_REF) {









	if (class != BPF_LDX &&









	    (kptr_field->type == BPF_KPTR_REF || kptr_field->type == BPF_KPTR_PERCPU)) {









		verbose(env, "store to referenced kptr disallowed\n");









		return -EACCES;









	}








@@ -5125,10 +5139,7 @@ static int check_map_kptr_access(struct bpf_verifier_env *env, u32 regno,







		 * value from map as PTR_TO_BTF_ID, with the correct type.









		 */









		mark_btf_ld_reg(env, cur_regs(env), value_regno, PTR_TO_BTF_ID, kptr_field->kptr.btf,









				kptr_field->kptr.btf_id,









				rcu_safe_kptr(kptr_field) && in_rcu_cs(env) ?









				PTR_MAYBE_NULL | MEM_RCU :









				PTR_MAYBE_NULL | PTR_UNTRUSTED);









				kptr_field->kptr.btf_id, btf_ld_kptr_type(env, kptr_field));









		/* For mark_ptr_or_null_reg */









		val_reg->id = ++env->id_gen;









	} else if (class == BPF_STX) {








@@ -5182,6 +5193,7 @@ static int check_map_access(struct bpf_verifier_env *env, u32 regno,







			switch (field->type) {









			case BPF_KPTR_UNREF:









			case BPF_KPTR_REF:









			case BPF_KPTR_PERCPU:









				if (src != ACCESS_DIRECT) {









					verbose(env, "kptr cannot be accessed indirectly by helper\n");









					return -EACCES;








@@ -7320,7 +7332,7 @@ static int process_kptr_func(struct bpf_verifier_env *env, int regno,







		verbose(env, "off=%d doesn't point to kptr\n", kptr_off);









		return -EACCES;









	}









	if (kptr_field->type != BPF_KPTR_REF) {









	if (kptr_field->type != BPF_KPTR_REF && kptr_field->type != BPF_KPTR_PERCPU) {









		verbose(env, "off=%d kptr isn't referenced kptr\n", kptr_off);









		return -EACCES;









	}








@@ -7831,8 +7843,10 @@ static int check_reg_type(struct bpf_verifier_env *env, u32 regno,







	if (base_type(arg_type) == ARG_PTR_TO_MEM)









		type &= ~DYNPTR_TYPE_FLAG_MASK;

















	if (meta->func_id == BPF_FUNC_kptr_xchg && type_is_alloc(type))









	if (meta->func_id == BPF_FUNC_kptr_xchg && type_is_alloc(type)) {









		type &= ~MEM_ALLOC;









		type &= ~MEM_PERCPU;









	}

















	for (i = 0; i < ARRAY_SIZE(compatible->types); i++) {









		expected = compatible->types[i];








@@ -7915,6 +7929,7 @@ static int check_reg_type(struct bpf_verifier_env *env, u32 regno,







		break;









	}









	case PTR_TO_BTF_ID | MEM_ALLOC:









	case PTR_TO_BTF_ID | MEM_PERCPU | MEM_ALLOC:









		if (meta->func_id != BPF_FUNC_spin_lock && meta->func_id != BPF_FUNC_spin_unlock &&









		    meta->func_id != BPF_FUNC_kptr_xchg) {









			verbose(env, "verifier internal error: unimplemented handling of MEM_ALLOC\n");








@@ -9882,8 +9897,11 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn







		if (func_id == BPF_FUNC_kptr_xchg) {









			ret_btf = meta.kptr_field->kptr.btf;









			ret_btf_id = meta.kptr_field->kptr.btf_id;









			if (!btf_is_kernel(ret_btf))









			if (!btf_is_kernel(ret_btf)) {









				regs[BPF_REG_0].type |= MEM_ALLOC;









				if (meta.kptr_field->type == BPF_KPTR_PERCPU)









					regs[BPF_REG_0].type |= MEM_PERCPU;









			}









		} else {









			if (fn->ret_btf_id == BPF_PTR_POISON) {









				verbose(env, "verifier internal error:");








@@ -10268,6 +10286,8 @@ enum special_kfunc_type {







	KF_bpf_dynptr_slice,









	KF_bpf_dynptr_slice_rdwr,









	KF_bpf_dynptr_clone,









	KF_bpf_percpu_obj_new_impl,









	KF_bpf_percpu_obj_drop_impl,









};

















BTF_SET_START(special_kfunc_set)








@@ -10288,6 +10308,8 @@ BTF_ID(func, bpf_dynptr_from_xdp)







BTF_ID(func, bpf_dynptr_slice)









BTF_ID(func, bpf_dynptr_slice_rdwr)









BTF_ID(func, bpf_dynptr_clone)









BTF_ID(func, bpf_percpu_obj_new_impl)









BTF_ID(func, bpf_percpu_obj_drop_impl)









BTF_SET_END(special_kfunc_set)

















BTF_ID_LIST(special_kfunc_list)








@@ -10310,6 +10332,8 @@ BTF_ID(func, bpf_dynptr_from_xdp)







BTF_ID(func, bpf_dynptr_slice)









BTF_ID(func, bpf_dynptr_slice_rdwr)









BTF_ID(func, bpf_dynptr_clone)









BTF_ID(func, bpf_percpu_obj_new_impl)









BTF_ID(func, bpf_percpu_obj_drop_impl)

















static bool is_kfunc_ret_null(struct bpf_kfunc_call_arg_meta *meta)









{








@@ -11004,7 +11028,17 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_







			}









			break;









		case KF_ARG_PTR_TO_ALLOC_BTF_ID:









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









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









				if (meta->func_id != special_kfunc_list[KF_bpf_obj_drop_impl]) {









					verbose(env, "arg#%d expected for bpf_obj_drop_impl()\n", i);









					return -EINVAL;









				}









			} else if (reg->type == (PTR_TO_BTF_ID | MEM_ALLOC | MEM_PERCPU)) {









				if (meta->func_id != special_kfunc_list[KF_bpf_percpu_obj_drop_impl]) {









					verbose(env, "arg#%d expected for bpf_percpu_obj_drop_impl()\n", i);









					return -EINVAL;









				}









			} else {









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









				return -EINVAL;









			}








@@ -11012,8 +11046,7 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_







				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]) {









			if (meta->btf == btf_vmlinux) {









				meta->arg_btf = reg->btf;









				meta->arg_btf_id = reg->btf_id;









			}








@@ -11413,6 +11446,7 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,







		/* Only exception is bpf_obj_new_impl */









		if (meta.btf != btf_vmlinux ||









		    (meta.func_id != special_kfunc_list[KF_bpf_obj_new_impl] &&









		     meta.func_id != special_kfunc_list[KF_bpf_percpu_obj_new_impl] &&









		     meta.func_id != special_kfunc_list[KF_bpf_refcount_acquire_impl])) {









			verbose(env, "acquire kernel function does not return PTR_TO_BTF_ID\n");









			return -EINVAL;








@@ -11426,11 +11460,16 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,







		ptr_type = btf_type_skip_modifiers(desc_btf, t->type, &ptr_type_id);

















		if (meta.btf == btf_vmlinux && btf_id_set_contains(&special_kfunc_set, meta.func_id)) {









			if (meta.func_id == special_kfunc_list[KF_bpf_obj_new_impl]) {









			if (meta.func_id == special_kfunc_list[KF_bpf_obj_new_impl] ||









			    meta.func_id == special_kfunc_list[KF_bpf_percpu_obj_new_impl]) {









				struct btf_struct_meta *struct_meta;









				struct btf *ret_btf;









				u32 ret_btf_id;

















				if (unlikely(!bpf_global_ma_set))









				if (meta.func_id == special_kfunc_list[KF_bpf_obj_new_impl] && !bpf_global_ma_set)









					return -ENOMEM;

















				if (meta.func_id == special_kfunc_list[KF_bpf_percpu_obj_new_impl] && !bpf_global_percpu_ma_set)









					return -ENOMEM;

















				if (((u64)(u32)meta.arg_constant.value) != meta.arg_constant.value) {








@@ -11443,24 +11482,38 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,















				/* This may be NULL due to user not supplying a BTF */









				if (!ret_btf) {









					verbose(env, "bpf_obj_new requires prog BTF\n");









					verbose(env, "bpf_obj_new/bpf_percpu_obj_new requires prog BTF\n");









					return -EINVAL;









				}

















				ret_t = btf_type_by_id(ret_btf, ret_btf_id);









				if (!ret_t || !__btf_type_is_struct(ret_t)) {









					verbose(env, "bpf_obj_new type ID argument must be of a struct\n");









					verbose(env, "bpf_obj_new/bpf_percpu_obj_new type ID argument must be of a struct\n");









					return -EINVAL;









				}

















				struct_meta = btf_find_struct_meta(ret_btf, ret_btf_id);









				if (meta.func_id == special_kfunc_list[KF_bpf_percpu_obj_new_impl]) {









					if (!__btf_type_is_scalar_struct(env, ret_btf, ret_t, 0)) {









						verbose(env, "bpf_percpu_obj_new type ID argument must be of a struct of scalars\n");









						return -EINVAL;









					}

















					if (struct_meta) {









						verbose(env, "bpf_percpu_obj_new type ID argument must not contain special fields\n");









						return -EINVAL;









					}









				}

















				mark_reg_known_zero(env, regs, BPF_REG_0);









				regs[BPF_REG_0].type = PTR_TO_BTF_ID | MEM_ALLOC;









				regs[BPF_REG_0].btf = ret_btf;









				regs[BPF_REG_0].btf_id = ret_btf_id;









				if (meta.func_id == special_kfunc_list[KF_bpf_percpu_obj_new_impl])









					regs[BPF_REG_0].type |= MEM_PERCPU;

















				insn_aux->obj_new_size = ret_t->size;









				insn_aux->kptr_struct_meta =









					btf_find_struct_meta(ret_btf, ret_btf_id);









				insn_aux->kptr_struct_meta = struct_meta;









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









				mark_reg_known_zero(env, regs, BPF_REG_0);









				regs[BPF_REG_0].type = PTR_TO_BTF_ID | MEM_ALLOC;








@@ -11597,7 +11650,8 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,







			regs[BPF_REG_0].id = ++env->id_gen;









	} else if (btf_type_is_void(t)) {









		if (meta.btf == btf_vmlinux && btf_id_set_contains(&special_kfunc_set, meta.func_id)) {









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









			if (meta.func_id == special_kfunc_list[KF_bpf_obj_drop_impl] ||









			    meta.func_id == special_kfunc_list[KF_bpf_percpu_obj_drop_impl]) {









				insn_aux->kptr_struct_meta =









					btf_find_struct_meta(meta.arg_btf,









							     meta.arg_btf_id);








@@ -18266,21 +18320,35 @@ static int fixup_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,







		insn->imm = BPF_CALL_IMM(desc->addr);









	if (insn->off)









		return 0;









	if (desc->func_id == special_kfunc_list[KF_bpf_obj_new_impl]) {









	if (desc->func_id == special_kfunc_list[KF_bpf_obj_new_impl] ||









	    desc->func_id == special_kfunc_list[KF_bpf_percpu_obj_new_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) };









		u64 obj_new_size = env->insn_aux_data[insn_idx].obj_new_size;

















		if (desc->func_id == special_kfunc_list[KF_bpf_percpu_obj_new_impl] && kptr_struct_meta) {









			verbose(env, "verifier internal error: NULL kptr_struct_meta expected at insn_idx %d\n",









				insn_idx);









			return -EFAULT;









		}

















		insn_buf[0] = BPF_MOV64_IMM(BPF_REG_1, obj_new_size);









		insn_buf[1] = addr[0];









		insn_buf[2] = addr[1];









		insn_buf[3] = *insn;









		*cnt = 4;









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









		   desc->func_id == special_kfunc_list[KF_bpf_percpu_obj_drop_impl] ||









		   desc->func_id == special_kfunc_list[KF_bpf_refcount_acquire_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) };

















		if (desc->func_id == special_kfunc_list[KF_bpf_percpu_obj_drop_impl] && kptr_struct_meta) {









			verbose(env, "verifier internal error: NULL kptr_struct_meta expected at insn_idx %d\n",









				insn_idx);









			return -EFAULT;









		}

















		if (desc->func_id == special_kfunc_list[KF_bpf_refcount_acquire_impl] &&









		    !kptr_struct_meta) {









			verbose(env, "verifier internal error: kptr_struct_meta expected at insn_idx %d\n",