In this patch, bpf_timer_set_sleepable_cb() is functionally equivalent to bpf_timer_set_callback(), to the exception that it enforces the timer to be started with BPF_F_TIMER_SLEEPABLE.
But given that bpf_timer_set_callback() is a helper when bpf_timer_set_sleepable_cb() is a kfunc, we need to teach the verifier about its attached callback. Marking that callback as sleepable will be done in a separate patch
Signed-off-by: Benjamin Tissoires bentiss@kernel.org
---
new in v3 (split from v2 02/10) --- kernel/bpf/helpers.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++-- kernel/bpf/verifier.c | 31 +++++++++++++++++++++++++++++-- 2 files changed, 75 insertions(+), 4 deletions(-)
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index f9add0abe40a..2c6dc3d0ffff 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -1108,6 +1108,7 @@ struct bpf_hrtimer { void __rcu *callback_fn; void *value; struct semaphore sleepable_lock; + bool is_sleepable; };
/* the actual struct hidden inside uapi struct bpf_timer */ @@ -1270,8 +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; @@ -1311,12 +1312,19 @@ BPF_CALL_3(bpf_timer_set_callback, struct bpf_timer_kern *, timer, void *, callb t->prog = prog; } rcu_assign_pointer(t->callback_fn, callback_fn); + t->is_sleepable = is_sleepable; up(&t->sleepable_lock); 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, @@ -1342,6 +1350,11 @@ BPF_CALL_3(bpf_timer_start, struct bpf_timer_kern *, timer, u64, nsecs, u64, fla goto out; }
+ if (t->is_sleepable && !(flags & BPF_F_TIMER_SLEEPABLE)) { + ret = -EINVAL; + goto out; + } + if (flags & BPF_F_TIMER_ABS) mode = HRTIMER_MODE_ABS_SOFT; else @@ -2606,6 +2619,36 @@ __bpf_kfunc void bpf_throw(u64 cookie) WARN(1, "A call to BPF exception callback should never return\n"); }
+/** + * bpf_timer_set_sleepable_cb() - Configure the timer to call %callback_fn + * static function in a sleepable context. + * @timer: The bpf_timer that needs to be configured + * @callback_fn: a static bpf function + * + * @returns %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. + * + * This kfunc is equivalent to %bpf_timer_set_callback except that it tells + * the verifier that the target callback is run in a sleepable context. + */ +__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 = {}; + + 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) @@ -2682,6 +2725,7 @@ BTF_ID_FLAGS(func, bpf_dynptr_is_null) BTF_ID_FLAGS(func, bpf_dynptr_is_rdonly) BTF_ID_FLAGS(func, bpf_dynptr_size) BTF_ID_FLAGS(func, bpf_dynptr_clone) +BTF_ID_FLAGS(func, bpf_timer_set_sleepable_cb) BTF_KFUNCS_END(common_btf_ids)
static const struct btf_kfunc_id_set common_kfunc_set = { diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 2b11687063ff..91e583c6feba 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -501,6 +501,8 @@ 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_async_callback_calling_kfunc(u32 btf_id); +static bool is_callback_calling_kfunc(u32 btf_id); static bool is_bpf_throw_kfunc(struct bpf_insn *insn);
static bool is_sync_callback_calling_function(enum bpf_func_id func_id) @@ -530,7 +532,8 @@ static bool is_sync_callback_calling_insn(struct bpf_insn *insn)
static bool is_async_callback_calling_insn(struct bpf_insn *insn) { - return (bpf_helper_call(insn) && is_async_callback_calling_function(insn->imm)); + return (bpf_helper_call(insn) && is_async_callback_calling_function(insn->imm)) || + (bpf_pseudo_kfunc_call(insn) && is_async_callback_calling_kfunc(insn->imm)); }
static bool is_storage_get_function(enum bpf_func_id func_id) @@ -9459,7 +9462,7 @@ static int push_callback_call(struct bpf_verifier_env *env, struct bpf_insn *ins */ env->subprog_info[subprog].is_cb = true; if (bpf_pseudo_kfunc_call(insn) && - !is_sync_callback_calling_kfunc(insn->imm)) { + !is_callback_calling_kfunc(insn->imm)) { verbose(env, "verifier bug: kfunc %s#%d not marked as callback-calling\n", func_id_name(insn->imm), insn->imm); return -EFAULT; @@ -10963,6 +10966,7 @@ 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) @@ -10989,6 +10993,7 @@ 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) @@ -11019,6 +11024,7 @@ 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) { @@ -11344,12 +11350,23 @@ static bool is_sync_callback_calling_kfunc(u32 btf_id) return btf_id == special_kfunc_list[KF_bpf_rbtree_add_impl]; }
+static bool is_async_callback_calling_kfunc(u32 btf_id) +{ + return btf_id == special_kfunc_list[KF_bpf_timer_set_sleepable_cb]; +} + static bool is_bpf_throw_kfunc(struct bpf_insn *insn) { return bpf_pseudo_kfunc_call(insn) && insn->off == 0 && insn->imm == special_kfunc_list[KF_bpf_throw]; }
+static bool is_callback_calling_kfunc(u32 btf_id) +{ + return is_sync_callback_calling_kfunc(btf_id) || + is_async_callback_calling_kfunc(btf_id); +} + static bool is_rbtree_lock_required_kfunc(u32 btf_id) { return is_bpf_rbtree_api_kfunc(btf_id); @@ -12120,6 +12137,16 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn, } }
+ if (is_async_callback_calling_kfunc(meta.func_id)) { + err = push_callback_call(env, insn, insn_idx, meta.subprogno, + set_timer_callback_state); + if (err) { + verbose(env, "kfunc %s#%d failed callback verification\n", + func_name, meta.func_id); + return err; + } + } + rcu_lock = is_kfunc_bpf_rcu_read_lock(&meta); rcu_unlock = is_kfunc_bpf_rcu_read_unlock(&meta);