Commit 4e814da0 authored by Kumar Kartikeya Dwivedi's avatar Kumar Kartikeya Dwivedi Committed by Alexei Starovoitov
Browse files

bpf: Allow locking bpf_spin_lock in allocated objects 



Allow locking a bpf_spin_lock in an allocated object, in addition to
already supported map value pointers. The handling is similar to that of
map values, by just preserving the reg->id of PTR_TO_BTF_ID | MEM_ALLOC
as well, and adjusting process_spin_lock to work with them and remember
the id in verifier state.

Refactor the existing process_spin_lock to work with PTR_TO_BTF_ID |
MEM_ALLOC in addition to PTR_TO_MAP_VALUE. We need to update the
reg_may_point_to_spin_lock which is used in mark_ptr_or_null_reg to
preserve reg->id, that will be used in env->cur_state->active_spin_lock
to remember the currently held spin lock.

Also update the comment describing bpf_spin_lock implementation details
to also talk about PTR_TO_BTF_ID | MEM_ALLOC type.

Signed-off-by: default avatarKumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20221118015614.2013203-9-memxor@gmail.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 865ce09a

kernel/bpf/helpers.c

+2 −0
Original line number Diff line number Diff line
@@ -336,6 +336,7 @@ const struct bpf_func_proto bpf_spin_lock_proto = { 
	.gpl_only	= false,

	.ret_type	= RET_VOID,

	.arg1_type	= ARG_PTR_TO_SPIN_LOCK,

	.arg1_btf_id    = BPF_PTR_POISON,

};



static inline void __bpf_spin_unlock_irqrestore(struct bpf_spin_lock *lock)
@@ -358,6 +359,7 @@ const struct bpf_func_proto bpf_spin_unlock_proto = { 
	.gpl_only	= false,

	.ret_type	= RET_VOID,

	.arg1_type	= ARG_PTR_TO_SPIN_LOCK,

	.arg1_btf_id    = BPF_PTR_POISON,

};



void copy_map_value_locked(struct bpf_map *map, void *dst, void *src,

kernel/bpf/verifier.c

+65 −25
Original line number Diff line number Diff line
@@ -451,10 +451,24 @@ static bool reg_type_not_null(enum bpf_reg_type type) 
		type == PTR_TO_SOCK_COMMON;

}



static struct btf_record *reg_btf_record(const struct bpf_reg_state *reg)

{

	struct btf_record *rec = NULL;

	struct btf_struct_meta *meta;



	if (reg->type == PTR_TO_MAP_VALUE) {

		rec = reg->map_ptr->record;

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

		meta = btf_find_struct_meta(reg->btf, reg->btf_id);

		if (meta)

			rec = meta->record;

	}

	return rec;

}



static bool reg_may_point_to_spin_lock(const struct bpf_reg_state *reg)

{

	return reg->type == PTR_TO_MAP_VALUE &&

	       btf_record_has_field(reg->map_ptr->record, BPF_SPIN_LOCK);

	return btf_record_has_field(reg_btf_record(reg), BPF_SPIN_LOCK);

}



static bool type_is_rdonly_mem(u32 type)
@@ -5564,23 +5578,26 @@ int check_kfunc_mem_size_reg(struct bpf_verifier_env *env, struct bpf_reg_state 
}



/* Implementation details:

 * bpf_map_lookup returns PTR_TO_MAP_VALUE_OR_NULL

 * bpf_map_lookup returns PTR_TO_MAP_VALUE_OR_NULL.

 * bpf_obj_new returns PTR_TO_BTF_ID | MEM_ALLOC | PTR_MAYBE_NULL.

 * Two bpf_map_lookups (even with the same key) will have different reg->id.

 * For traditional PTR_TO_MAP_VALUE the verifier clears reg->id after

 * value_or_null->value transition, since the verifier only cares about

 * the range of access to valid map value pointer and doesn't care about actual

 * address of the map element.

 * Two separate bpf_obj_new will also have different reg->id.

 * For traditional PTR_TO_MAP_VALUE or PTR_TO_BTF_ID | MEM_ALLOC, the verifier

 * clears reg->id after value_or_null->value transition, since the verifier only

 * cares about the range of access to valid map value pointer and doesn't care

 * about actual address of the map element.

 * For maps with 'struct bpf_spin_lock' inside map value the verifier keeps

 * reg->id > 0 after value_or_null->value transition. By doing so

 * two bpf_map_lookups will be considered two different pointers that

 * point to different bpf_spin_locks.

 * point to different bpf_spin_locks. Likewise for pointers to allocated objects

 * returned from bpf_obj_new.

 * The verifier allows taking only one bpf_spin_lock at a time to avoid

 * dead-locks.

 * Since only one bpf_spin_lock is allowed the checks are simpler than

 * reg_is_refcounted() logic. The verifier needs to remember only

 * one spin_lock instead of array of acquired_refs.

 * cur_state->active_spin_lock remembers which map value element got locked

 * and clears it after bpf_spin_unlock.

 * cur_state->active_spin_lock remembers which map value element or allocated

 * object got locked and clears it after bpf_spin_unlock.

 */

static int process_spin_lock(struct bpf_verifier_env *env, int regno,

			     bool is_lock)
@@ -5588,8 +5605,10 @@ static int process_spin_lock(struct bpf_verifier_env *env, int regno, 
	struct bpf_reg_state *regs = cur_regs(env), *reg = &regs[regno];

	struct bpf_verifier_state *cur = env->cur_state;

	bool is_const = tnum_is_const(reg->var_off);

	struct bpf_map *map = reg->map_ptr;

	u64 val = reg->var_off.value;

	struct bpf_map *map = NULL;

	struct btf *btf = NULL;

	struct btf_record *rec;



	if (!is_const) {

		verbose(env,
@@ -5597,19 +5616,27 @@ static int process_spin_lock(struct bpf_verifier_env *env, int regno, 
			regno);

		return -EINVAL;

	}

	if (reg->type == PTR_TO_MAP_VALUE) {

		map = reg->map_ptr;

		if (!map->btf) {

			verbose(env,

				"map '%s' has to have BTF in order to use bpf_spin_lock\n",

				map->name);

			return -EINVAL;

		}

	if (!btf_record_has_field(map->record, BPF_SPIN_LOCK)) {

		verbose(env, "map '%s' has no valid bpf_spin_lock\n", map->name);

	} else {

		btf = reg->btf;

	}



	rec = reg_btf_record(reg);

	if (!btf_record_has_field(rec, BPF_SPIN_LOCK)) {

		verbose(env, "%s '%s' has no valid bpf_spin_lock\n", map ? "map" : "local",

			map ? map->name : "kptr");

		return -EINVAL;

	}

	if (map->record->spin_lock_off != val + reg->off) {

	if (rec->spin_lock_off != val + reg->off) {

		verbose(env, "off %lld doesn't point to 'struct bpf_spin_lock' that is at %d\n",

			val + reg->off, map->record->spin_lock_off);

			val + reg->off, rec->spin_lock_off);

		return -EINVAL;

	}

	if (is_lock) {
@@ -5815,13 +5842,19 @@ static const struct bpf_reg_types int_ptr_types = { 
	},

};



static const struct bpf_reg_types spin_lock_types = {

	.types = {

		PTR_TO_MAP_VALUE,

		PTR_TO_BTF_ID | MEM_ALLOC,

	}

};



static const struct bpf_reg_types fullsock_types = { .types = { PTR_TO_SOCKET } };

static const struct bpf_reg_types scalar_types = { .types = { SCALAR_VALUE } };

static const struct bpf_reg_types context_types = { .types = { PTR_TO_CTX } };

static const struct bpf_reg_types ringbuf_mem_types = { .types = { PTR_TO_MEM | MEM_RINGBUF } };

static const struct bpf_reg_types const_map_ptr_types = { .types = { CONST_PTR_TO_MAP } };

static const struct bpf_reg_types btf_ptr_types = { .types = { PTR_TO_BTF_ID } };

static const struct bpf_reg_types spin_lock_types = { .types = { PTR_TO_MAP_VALUE } };

static const struct bpf_reg_types percpu_btf_ptr_types = { .types = { PTR_TO_BTF_ID | MEM_PERCPU } };

static const struct bpf_reg_types func_ptr_types = { .types = { PTR_TO_FUNC } };

static const struct bpf_reg_types stack_ptr_types = { .types = { PTR_TO_STACK } };
@@ -5946,6 +5979,11 @@ static int check_reg_type(struct bpf_verifier_env *env, u32 regno, 
				return -EACCES;

			}

		}

	} else if (type_is_alloc(reg->type)) {

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

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

			return -EFAULT;

		}

	}



	return 0;
@@ -6062,7 +6100,8 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg, 
		goto skip_type_check;



	/* arg_btf_id and arg_size are in a union. */

	if (base_type(arg_type) == ARG_PTR_TO_BTF_ID)

	if (base_type(arg_type) == ARG_PTR_TO_BTF_ID ||

	    base_type(arg_type) == ARG_PTR_TO_SPIN_LOCK)

		arg_btf_id = fn->arg_btf_id[arg];



	err = check_reg_type(env, regno, arg_type, arg_btf_id, meta);
@@ -6680,9 +6719,10 @@ static bool check_btf_id_ok(const struct bpf_func_proto *fn) 
	int i;



	for (i = 0; i < ARRAY_SIZE(fn->arg_type); i++) {

		if (base_type(fn->arg_type[i]) == ARG_PTR_TO_BTF_ID && !fn->arg_btf_id[i])

			return false;



		if (base_type(fn->arg_type[i]) == ARG_PTR_TO_BTF_ID)

			return !!fn->arg_btf_id[i];

		if (base_type(fn->arg_type[i]) == ARG_PTR_TO_SPIN_LOCK)

			return fn->arg_btf_id[i] == BPF_PTR_POISON;

		if (base_type(fn->arg_type[i]) != ARG_PTR_TO_BTF_ID && fn->arg_btf_id[i] &&

		    /* arg_btf_id and arg_size are in a union. */

		    (base_type(fn->arg_type[i]) != ARG_PTR_TO_MEM ||