Re: [PATCH bpf-next 08/18] bpf: add support for KF_ARG_PTR_TO_WORKQUEUE

On Tue, Apr 16, 2024 at 04:08:21PM +0200, Benjamin Tissoires wrote:

Introduce support for KF_ARG_PTR_TO_WORKQUEUE. The kfuncs will use bpf_wq as argument and that will be recognized as workqueue argument by verifier. bpf_wq_kern casting can happen inside kfunc, but using bpf_wq in argument makes life easier for users who work with non-kern type in BPF progs.

Duplicate process_timer_func into process_wq_func. meta argument is only needed to ensure bpf_wq_init's workqueue and map arguments are coming from the same map (map_uid logic is necessary for correct inner-map handling), so also amend check_kfunc_args() to match what helpers functions check is doing.

Signed-off-by: Benjamin Tissoires bentiss@kernel.org

kernel/bpf/verifier.c | 86 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 86 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index deaf2e1ab690..112faf2cd7e9 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -332,6 +332,10 @@ struct bpf_kfunc_call_arg_meta { u8 spi; u8 frameno; } iter;

• struct {

• struct bpf_map *ptr;
  

• int uid;
  

• } map; u64 mem_size;

}; @@ -7598,6 +7602,43 @@ static int process_timer_func(struct bpf_verifier_env *env, int regno, return 0; } +static int process_wq_func(struct bpf_verifier_env *env, int regno,

• 	   struct bpf_kfunc_call_arg_meta *meta)
  

+{

• struct bpf_reg_state *regs = cur_regs(env), *reg = &regs[regno];
• bool is_const = tnum_is_const(reg->var_off);
• struct bpf_map *map = reg->map_ptr;
• u64 val = reg->var_off.value;
• if (!is_const) {

• verbose(env,
  

• 	"R%d doesn't have constant offset. bpf_wq has to be at the constant offset\n",
  

• 	regno);
  

• return -EINVAL;
  

• }

This check is unnecessary. Before calling into this function it goes as: switch (kf_arg_type) { case KF_ARG_PTR_TO_MAP: ... your new checks ... fallthrough; case KF_ARG_PTR_TO_CTX: arg_type |= OBJ_RELEASE; break;

check_func_arg_reg_off() if (arg_type_is_release(arg_type) return __check_ptr_off_reg() // that does offset checks

• if (!map->btf) {

• verbose(env, "map '%s' has to have BTF in order to use bpf_wq\n",
  

• 	map->name);
  

• return -EINVAL;
  

• }
• if (!btf_record_has_field(map->record, BPF_WORKQUEUE)) {

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

• return -EINVAL;
  

• }

above two are also unnecessary. wq_off will be negative otherwise.

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

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

• 	val + reg->off, map->record->wq_off);
  

• return -EINVAL;
  

• }

only this one is needed, but I need to study the rest of the patches.

• if (meta->map.ptr) {

• verbose(env, "verifier bug. Two map pointers in a workqueue helper\n");
  

• return -EFAULT;
  

• }

this was checked already as well.

• meta->map.uid = reg->map_uid;
• meta->map.ptr = map;
• return 0;

+}

static int process_kptr_func(struct bpf_verifier_env *env, int regno, struct bpf_call_arg_meta *meta) { @@ -10843,6 +10884,7 @@ enum { KF_ARG_LIST_NODE_ID, KF_ARG_RB_ROOT_ID, KF_ARG_RB_NODE_ID,

• KF_ARG_WORKQUEUE_ID,

}; BTF_ID_LIST(kf_arg_btf_ids) @@ -10851,6 +10893,7 @@ BTF_ID(struct, bpf_list_head) BTF_ID(struct, bpf_list_node) BTF_ID(struct, bpf_rb_root) BTF_ID(struct, bpf_rb_node) +BTF_ID(struct, bpf_wq) static bool __is_kfunc_ptr_arg_type(const struct btf *btf, const struct btf_param *arg, int type) @@ -10894,6 +10937,11 @@ static bool is_kfunc_arg_rbtree_node(const struct btf *btf, const struct btf_par return __is_kfunc_ptr_arg_type(btf, arg, KF_ARG_RB_NODE_ID); } +static bool is_kfunc_arg_wq(const struct btf *btf, const struct btf_param *arg) +{

• return __is_kfunc_ptr_arg_type(btf, arg, KF_ARG_WORKQUEUE_ID);

+}

static bool is_kfunc_arg_callback(struct bpf_verifier_env *env, const struct btf *btf, const struct btf_param *arg) { @@ -10963,6 +11011,7 @@ enum kfunc_ptr_arg_type { KF_ARG_PTR_TO_NULL, KF_ARG_PTR_TO_CONST_STR, KF_ARG_PTR_TO_MAP,

• KF_ARG_PTR_TO_WORKQUEUE,

}; enum special_kfunc_type { @@ -11119,6 +11168,9 @@ get_kfunc_ptr_arg_type(struct bpf_verifier_env *env, if (is_kfunc_arg_map(meta->btf, &args[argno])) return KF_ARG_PTR_TO_MAP;

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

• return KF_ARG_PTR_TO_WORKQUEUE;
  

• if ((base_type(reg->type) == PTR_TO_BTF_ID || reg2btf_ids[base_type(reg->type)])) { if (!btf_type_is_struct(ref_t)) { verbose(env, "kernel function %s args#%d pointer type %s %s is not supported\n",

@@ -11720,6 +11772,30 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_ case KF_ARG_PTR_TO_NULL: continue; case KF_ARG_PTR_TO_MAP:

• 	if (meta->map.ptr) {
  

• 		/* Use map_uid (which is unique id of inner map) to reject:
  

• 		 * inner_map1 = bpf_map_lookup_elem(outer_map, key1)
  

• 		 * inner_map2 = bpf_map_lookup_elem(outer_map, key2)
  

• 		 * if (inner_map1 && inner_map2) {
  

• 		 *     timer = bpf_map_lookup_elem(inner_map1);
  

• 		 *     if (timer)
  

• 		 *         // mismatch would have been allowed
  

• 		 *         bpf_timer_init(timer, inner_map2);
  

adjust the comment too. Here it can only be wq.

• 		 * }
  

• 		 *
  

• 		 * Comparing map_ptr is enough to distinguish normal and outer maps.
  

• 		 */
  

• 		if (meta->map.ptr != reg->map_ptr ||
  

• 		    meta->map.uid != reg->map_uid) {
  

let's also gate this check with map->record->wq_off. Otherwise it will trigger for maps that don't have wq field.

Copy paste is a bit unfortunate, but fine. We can clean it up later.

• 			verbose(env,
  

• 				"workqueue pointer in R1 map_uid=%d doesn't match map pointer in R2 map_uid=%d\n",
  

• 				meta->map.uid, reg->map_uid);
  

• 			return -EINVAL;
  

• 		}
  

• 	}
  

• 	meta->map.ptr = reg->map_ptr;
  

• 	meta->map.uid = reg->map_uid;
  

• 	fallthrough;
  

  case KF_ARG_PTR_TO_ALLOC_BTF_ID: case KF_ARG_PTR_TO_BTF_ID: if (!is_kfunc_trusted_args(meta) && !is_kfunc_rcu(meta))

@@ -11752,6 +11828,7 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_ case KF_ARG_PTR_TO_CALLBACK: case KF_ARG_PTR_TO_REFCOUNTED_KPTR: case KF_ARG_PTR_TO_CONST_STR:

• case KF_ARG_PTR_TO_WORKQUEUE:
  /* Trusted by default */
  break;
  

  default:

@@ -12038,6 +12115,15 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_ if (ret) return ret; break;

• case KF_ARG_PTR_TO_WORKQUEUE:
  

• 	if (reg->type != PTR_TO_MAP_VALUE) {
  

• 		verbose(env, "arg#%d doesn't point to a map value\n", i);
  

• 		return -EINVAL;
  

• 	}
  

• 	ret = process_wq_func(env, regno, meta);
  

• 	if (ret < 0)
  

• 		return ret;
  

• 	break;
  

  } }

-- 2.44.0