They are implemented as a kfunc, which means a little bit of tweaks in the verifier.
Signed-off-by: Benjamin Tissoires bentiss@kernel.org
---
changes in v2 (compared to the one attaches to v1 0/9): - make use of a kfunc - add a (non-used) BPF_F_TIMER_SLEEPABLE - the callback is *not* called, it makes the kernel crashes --- include/linux/bpf_verifier.h | 2 + include/uapi/linux/bpf.h | 12 +++++ kernel/bpf/helpers.c | 105 ++++++++++++++++++++++++++++++++++++++++--- kernel/bpf/verifier.c | 72 ++++++++++++++++++++++++++--- 4 files changed, 180 insertions(+), 11 deletions(-)
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h index 84365e6dd85d..789ef5fec547 100644 --- a/include/linux/bpf_verifier.h +++ b/include/linux/bpf_verifier.h @@ -426,6 +426,7 @@ struct bpf_verifier_state { * while they are still in use. */ bool used_as_loop_entry; + bool in_sleepable;
/* first and last insn idx of this verifier state */ u32 first_insn_idx; @@ -626,6 +627,7 @@ struct bpf_subprog_info { bool is_async_cb: 1; bool is_exception_cb: 1; bool args_cached: 1; + bool is_sleepable: 1;
u8 arg_cnt; struct bpf_subprog_arg_info args[MAX_BPF_FUNC_REG_ARGS]; diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index d96708380e52..0838597028a9 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -7427,6 +7427,18 @@ enum { BPF_F_TIMER_CPU_PIN = (1ULL << 1), };
+/* Extra flags to control bpf_timer_init() behaviour, in addition to CLOCK_*. + * - BPF_F_TIMER_SLEEPABLE: Timer will run in a workqueue in a sleepable + * context. + */ +enum { + /* CLOCK_* are using bits 0 to 3 */ + BPF_F_TIMER_SLEEPABLE = (1ULL << 4), + __MAX_BPF_F_TIMER_INIT, +}; + +#define MAX_BPF_F_TIMER_INIT __MAX_BPF_F_TIMER_INIT + /* BPF numbers iterator state */ struct bpf_iter_num { /* opaque iterator state; having __u64 here allows to preserve correct diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index 4db1c658254c..2dbc09ce841a 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -1097,9 +1097,11 @@ const struct bpf_func_proto bpf_snprintf_proto = { */ struct bpf_hrtimer { struct hrtimer timer; + struct work_struct work; struct bpf_map *map; struct bpf_prog *prog; void __rcu *callback_fn; + void __rcu *sleepable_cb_fn; void *value; };
@@ -1113,18 +1115,59 @@ struct bpf_timer_kern { struct bpf_spin_lock lock; } __attribute__((aligned(8)));
+static void bpf_timer_work_cb(struct work_struct *work) +{ + struct bpf_hrtimer *t = container_of(work, struct bpf_hrtimer, work); + struct bpf_map *map = t->map; + void *value = t->value; + bpf_callback_t callback_fn; + void *key; + u32 idx; + + BTF_TYPE_EMIT(struct bpf_timer); + + rcu_read_lock(); + callback_fn = rcu_dereference(t->sleepable_cb_fn); + rcu_read_unlock(); + if (!callback_fn) + return; + + /* FIXME: do we need any locking? */ + if (map->map_type == BPF_MAP_TYPE_ARRAY) { + struct bpf_array *array = container_of(map, struct bpf_array, map); + + /* compute the key */ + idx = ((char *)value - array->value) / array->elem_size; + key = &idx; + } else { /* hash or lru */ + key = value - round_up(map->key_size, 8); + } + + /* FIXME: this crashes the system with + * BUG: kernel NULL pointer dereference, address: 000000000000000b + */ + /* callback_fn((u64)(long)map, (u64)(long)key, (u64)(long)value, 0, 0); */ + /* The verifier checked that return value is zero. */ +} + static DEFINE_PER_CPU(struct bpf_hrtimer *, hrtimer_running);
static enum hrtimer_restart bpf_timer_cb(struct hrtimer *hrtimer) { struct bpf_hrtimer *t = container_of(hrtimer, struct bpf_hrtimer, timer); + bpf_callback_t callback_fn, sleepable_cb_fn; struct bpf_map *map = t->map; void *value = t->value; - bpf_callback_t callback_fn; void *key; u32 idx;
BTF_TYPE_EMIT(struct bpf_timer); + sleepable_cb_fn = rcu_dereference_check(t->sleepable_cb_fn, rcu_read_lock_bh_held()); + if (sleepable_cb_fn) { + schedule_work(&t->work); + goto out; + } + callback_fn = rcu_dereference_check(t->callback_fn, rcu_read_lock_bh_held()); if (!callback_fn) goto out; @@ -1154,10 +1197,14 @@ static enum hrtimer_restart bpf_timer_cb(struct hrtimer *hrtimer) return HRTIMER_NORESTART; }
+#define BPF_TIMER_CLOCK_MASK (MAX_CLOCKS - 1) /* 0xf */ +#define BPF_TIMER_FLAGS_MASK GENMASK_ULL(63, 4) + BPF_CALL_3(bpf_timer_init, struct bpf_timer_kern *, timer, struct bpf_map *, map, u64, flags) { - clockid_t clockid = flags & (MAX_CLOCKS - 1); + clockid_t clockid = flags & BPF_TIMER_CLOCK_MASK; + u64 bpf_timer_flags = flags & BPF_TIMER_FLAGS_MASK; struct bpf_hrtimer *t; int ret = 0;
@@ -1168,7 +1215,7 @@ BPF_CALL_3(bpf_timer_init, struct bpf_timer_kern *, timer, struct bpf_map *, map if (in_nmi()) return -EOPNOTSUPP;
- if (flags >= MAX_CLOCKS || + if (bpf_timer_flags & ~(BPF_F_TIMER_SLEEPABLE) || /* similar to timerfd except _ALARM variants are not supported */ (clockid != CLOCK_MONOTONIC && clockid != CLOCK_REALTIME && @@ -1190,7 +1237,10 @@ BPF_CALL_3(bpf_timer_init, struct bpf_timer_kern *, timer, struct bpf_map *, map t->map = map; t->prog = NULL; rcu_assign_pointer(t->callback_fn, NULL); + rcu_assign_pointer(t->sleepable_cb_fn, NULL); + /* FIXME: probably do something about the SLEEPABLE flag */ hrtimer_init(&t->timer, clockid, HRTIMER_MODE_REL_SOFT); + INIT_WORK(&t->work, bpf_timer_work_cb); t->timer.function = bpf_timer_cb; WRITE_ONCE(timer->timer, t); /* Guarantee the order between timer->timer and map->usercnt. So @@ -1221,8 +1271,8 @@ static const struct bpf_func_proto bpf_timer_init_proto = { .arg3_type = ARG_ANYTHING, };
-BPF_CALL_3(bpf_timer_set_callback, struct bpf_timer_kern *, timer, void *, callback_fn, - struct bpf_prog_aux *, aux) +static int __bpf_timer_set_callback(struct bpf_timer_kern *timer, void *callback_fn, + struct bpf_prog_aux *aux, bool is_sleepable) { struct bpf_prog *prev, *prog = aux->prog; struct bpf_hrtimer *t; @@ -1260,12 +1310,24 @@ BPF_CALL_3(bpf_timer_set_callback, struct bpf_timer_kern *, timer, void *, callb bpf_prog_put(prev); t->prog = prog; } - rcu_assign_pointer(t->callback_fn, callback_fn); + if (is_sleepable) { + rcu_assign_pointer(t->sleepable_cb_fn, callback_fn); + rcu_assign_pointer(t->callback_fn, NULL); + } else { + rcu_assign_pointer(t->callback_fn, callback_fn); + rcu_assign_pointer(t->sleepable_cb_fn, NULL); + } out: __bpf_spin_unlock_irqrestore(&timer->lock); return ret; }
+BPF_CALL_3(bpf_timer_set_callback, struct bpf_timer_kern *, timer, void *, callback_fn, + struct bpf_prog_aux *, aux) +{ + return __bpf_timer_set_callback(timer, callback_fn, aux, false); +} + static const struct bpf_func_proto bpf_timer_set_callback_proto = { .func = bpf_timer_set_callback, .gpl_only = true, @@ -1353,6 +1415,7 @@ BPF_CALL_1(bpf_timer_cancel, struct bpf_timer_kern *, timer) * if it was running. */ ret = ret ?: hrtimer_cancel(&t->timer); + ret = ret ?: cancel_work_sync(&t->work); return ret; }
@@ -1407,6 +1470,8 @@ void bpf_timer_cancel_and_free(void *val) */ if (this_cpu_read(hrtimer_running) != t) hrtimer_cancel(&t->timer); + + cancel_work_sync(&t->work); kfree(t); }
@@ -2542,6 +2607,33 @@ __bpf_kfunc void bpf_throw(u64 cookie) WARN(1, "A call to BPF exception callback should never return\n"); }
+/* FIXME: use kernel doc style */ +/* Description + * Configure the timer to call *callback_fn* static function in a + * sleepable context. + * Return + * 0 on success. + * **-EINVAL** if *timer* was not initialized with bpf_timer_init() earlier. + * **-EPERM** if *timer* is in a map that doesn't have any user references. + * The user space should either hold a file descriptor to a map with timers + * or pin such map in bpffs. When map is unpinned or file descriptor is + * closed all timers in the map will be cancelled and freed. + */ +__bpf_kfunc int bpf_timer_set_sleepable_cb(struct bpf_timer_kern *timer, + int (callback_fn)(void *map, int *key, struct bpf_timer *timer)) +{ + struct bpf_throw_ctx ctx = {}; + + /* FIXME: definietely not sure this is OK */ + arch_bpf_stack_walk(bpf_stack_walker, &ctx); + WARN_ON_ONCE(!ctx.aux); + + if (!ctx.aux) + return -EINVAL; + + return __bpf_timer_set_callback(timer, (void *)callback_fn, ctx.aux, true); +} + __bpf_kfunc_end_defs();
BTF_KFUNCS_START(generic_btf_ids) @@ -2573,6 +2665,7 @@ BTF_ID_FLAGS(func, bpf_task_get_cgroup1, KF_ACQUIRE | KF_RCU | KF_RET_NULL) #endif BTF_ID_FLAGS(func, bpf_task_from_pid, KF_ACQUIRE | KF_RET_NULL) BTF_ID_FLAGS(func, bpf_throw) +BTF_ID_FLAGS(func, bpf_timer_set_sleepable_cb) BTF_KFUNCS_END(generic_btf_ids)
static const struct btf_kfunc_id_set generic_kfunc_set = { diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 7831adba9abf..67da3f7bddb5 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -503,6 +503,8 @@ static bool is_dynptr_ref_function(enum bpf_func_id func_id) static bool is_sync_callback_calling_kfunc(u32 btf_id); static bool is_bpf_throw_kfunc(struct bpf_insn *insn);
+static bool is_bpf_timer_set_sleepable_cb_kfunc(u32 btf_id); + static bool is_sync_callback_calling_function(enum bpf_func_id func_id) { return func_id == BPF_FUNC_for_each_map_elem || @@ -513,7 +515,8 @@ static bool is_sync_callback_calling_function(enum bpf_func_id func_id)
static bool is_async_callback_calling_function(enum bpf_func_id func_id) { - return func_id == BPF_FUNC_timer_set_callback; + return func_id == BPF_FUNC_timer_set_callback || + is_bpf_timer_set_sleepable_cb_kfunc(func_id); }
static bool is_callback_calling_function(enum bpf_func_id func_id) @@ -1414,6 +1417,7 @@ static int copy_verifier_state(struct bpf_verifier_state *dst_state, } dst_state->speculative = src->speculative; dst_state->active_rcu_lock = src->active_rcu_lock; + dst_state->in_sleepable = src->in_sleepable; dst_state->curframe = src->curframe; dst_state->active_lock.ptr = src->active_lock.ptr; dst_state->active_lock.id = src->active_lock.id; @@ -2413,6 +2417,7 @@ static struct bpf_verifier_state *push_async_cb(struct bpf_verifier_env *env, * Initialize it similar to do_check_common(). */ elem->st.branches = 1; + elem->st.in_sleepable = env->subprog_info[subprog].is_sleepable; frame = kzalloc(sizeof(*frame), GFP_KERNEL); if (!frame) goto err; @@ -5257,7 +5262,8 @@ static int map_kptr_match_type(struct bpf_verifier_env *env,
static bool in_sleepable(struct bpf_verifier_env *env) { - return env->prog->aux->sleepable; + return env->prog->aux->sleepable || + (env->cur_state && env->cur_state->in_sleepable); }
/* The non-sleepable programs and sleepable programs with explicit bpf_rcu_read_lock() @@ -5439,6 +5445,26 @@ static int check_map_access(struct bpf_verifier_env *env, u32 regno, return -EACCES; } break; + case BPF_TIMER: + /* FIXME: kptr does the above, should we use the same? */ + if (src != ACCESS_DIRECT) { + verbose(env, "bpf_timer cannot be accessed indirectly by helper\n"); + return -EACCES; + } + if (!tnum_is_const(reg->var_off)) { + verbose(env, "bpf_timer access cannot have variable offset\n"); + return -EACCES; + } + if (p != off + reg->var_off.value) { + verbose(env, "bpf_timer access misaligned expected=%u off=%llu\n", + p, off + reg->var_off.value); + return -EACCES; + } + if (size != bpf_size_to_bytes(BPF_DW)) { + verbose(env, "bpf_timer access size must be BPF_DW\n"); + return -EACCES; + } + break; default: verbose(env, "%s cannot be accessed directly by load/store\n", btf_field_type_name(field->type)); @@ -9439,11 +9465,13 @@ static int push_callback_call(struct bpf_verifier_env *env, struct bpf_insn *ins
if (insn->code == (BPF_JMP | BPF_CALL) && insn->src_reg == 0 && - insn->imm == BPF_FUNC_timer_set_callback) { + (insn->imm == BPF_FUNC_timer_set_callback || + is_bpf_timer_set_sleepable_cb_kfunc(insn->imm))) { struct bpf_verifier_state *async_cb;
/* there is no real recursion here. timer callbacks are async */ env->subprog_info[subprog].is_async_cb = true; + env->subprog_info[subprog].is_sleepable = is_bpf_timer_set_sleepable_cb_kfunc(insn->imm); async_cb = push_async_cb(env, env->subprog_info[subprog].start, insn_idx, subprog); if (!async_cb) @@ -10412,6 +10440,10 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn break; }
+ if (is_bpf_timer_set_sleepable_cb_kfunc(func_id)) + err = push_callback_call(env, insn, insn_idx, meta.subprogno, + set_timer_callback_state); + if (err) return err;
@@ -10789,6 +10821,7 @@ enum { KF_ARG_LIST_NODE_ID, KF_ARG_RB_ROOT_ID, KF_ARG_RB_NODE_ID, + KF_ARG_TIMER_ID, };
BTF_ID_LIST(kf_arg_btf_ids) @@ -10797,6 +10830,7 @@ 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_timer_kern)
static bool __is_kfunc_ptr_arg_type(const struct btf *btf, const struct btf_param *arg, int type) @@ -10840,6 +10874,12 @@ 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_timer(const struct btf *btf, const struct btf_param *arg) +{ + bool ret = __is_kfunc_ptr_arg_type(btf, arg, KF_ARG_TIMER_ID); + return ret; +} + static bool is_kfunc_arg_callback(struct bpf_verifier_env *env, const struct btf *btf, const struct btf_param *arg) { @@ -10908,6 +10948,7 @@ enum kfunc_ptr_arg_type { KF_ARG_PTR_TO_RB_NODE, KF_ARG_PTR_TO_NULL, KF_ARG_PTR_TO_CONST_STR, + KF_ARG_PTR_TO_TIMER, };
enum special_kfunc_type { @@ -10934,6 +10975,7 @@ enum special_kfunc_type { KF_bpf_percpu_obj_drop_impl, KF_bpf_throw, KF_bpf_iter_css_task_new, + KF_bpf_timer_set_sleepable_cb, };
BTF_SET_START(special_kfunc_set) @@ -10960,6 +11002,7 @@ BTF_ID(func, bpf_throw) #ifdef CONFIG_CGROUPS BTF_ID(func, bpf_iter_css_task_new) #endif +BTF_ID(func, bpf_timer_set_sleepable_cb) BTF_SET_END(special_kfunc_set)
BTF_ID_LIST(special_kfunc_list) @@ -10990,6 +11033,7 @@ BTF_ID(func, bpf_iter_css_task_new) #else BTF_ID_UNUSED #endif +BTF_ID(func, bpf_timer_set_sleepable_cb)
static bool is_kfunc_ret_null(struct bpf_kfunc_call_arg_meta *meta) { @@ -11061,6 +11105,9 @@ get_kfunc_ptr_arg_type(struct bpf_verifier_env *env, if (is_kfunc_arg_const_str(meta->btf, &args[argno])) return KF_ARG_PTR_TO_CONST_STR;
+ if (is_kfunc_arg_timer(meta->btf, &args[argno])) + return KF_ARG_PTR_TO_TIMER; + 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", @@ -11318,6 +11365,11 @@ static bool is_bpf_throw_kfunc(struct bpf_insn *insn) insn->imm == special_kfunc_list[KF_bpf_throw]; }
+static bool is_bpf_timer_set_sleepable_cb_kfunc(u32 btf_id) +{ + return btf_id == special_kfunc_list[KF_bpf_timer_set_sleepable_cb]; +} + static bool is_rbtree_lock_required_kfunc(u32 btf_id) { return is_bpf_rbtree_api_kfunc(btf_id); @@ -11693,6 +11745,7 @@ 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_TIMER: /* Trusted by default */ break; default: @@ -11973,6 +12026,9 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_ if (ret) return ret; break; + case KF_ARG_PTR_TO_TIMER: + /* FIXME: should we do anything here? */ + break; } }
@@ -15591,7 +15647,9 @@ static int visit_insn(int t, struct bpf_verifier_env *env) return DONE_EXPLORING;
case BPF_CALL: - if (insn->src_reg == 0 && insn->imm == BPF_FUNC_timer_set_callback) + if (insn->src_reg == 0 && + (insn->imm == BPF_FUNC_timer_set_callback || + is_bpf_timer_set_sleepable_cb_kfunc(insn->imm))) /* Mark this call insn as a prune point to trigger * is_state_visited() check before call itself is * processed by __check_func_call(). Otherwise new @@ -16767,6 +16825,9 @@ static bool states_equal(struct bpf_verifier_env *env, if (old->active_rcu_lock != cur->active_rcu_lock) return false;
+ if (old->in_sleepable != cur->in_sleepable) + return false; + /* for states to be equal callsites have to be the same * and all frame states need to be equivalent */ @@ -19644,7 +19705,8 @@ static int do_misc_fixups(struct bpf_verifier_env *env) continue; }
- if (insn->imm == BPF_FUNC_timer_set_callback) { + if (insn->imm == BPF_FUNC_timer_set_callback || + is_bpf_timer_set_sleepable_cb_kfunc(insn->imm)) { /* The verifier will process callback_fn as many times as necessary * with different maps and the register states prepared by * set_timer_callback_state will be accurate.