diff mbox series

[RFC,bpf-next,v3,06/16] bpf/helpers: introduce bpf_timer_set_sleepable_cb() kfunc

Message ID 20240221-hid-bpf-sleepable-v3-6-1fb378ca6301@kernel.org
State New
Headers show
Series sleepable bpf_timer (was: allow HID-BPF to do device IOs) | expand

Commit Message

Benjamin Tissoires Feb. 21, 2024, 4:25 p.m. UTC 
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(-)

Comments

Alexei Starovoitov Feb. 22, 2024, 8:53 p.m. UTC | #1 
On Wed, Feb 21, 2024 at 8:25 AM Benjamin Tissoires <bentiss@kernel.org> wrote:
>
> 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);

Sorry. Why such complexity?
Please see how do_misc_fixups() handles BPF_FUNC_timer_set_callback.
Eduard Zingerman Feb. 23, 2024, 3:10 p.m. UTC | #2 
On Wed, 2024-02-21 at 17:25 +0100, Benjamin Tissoires wrote:

[...]

> @@ -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)) {

I think that it's better to check specific kfunc id here:

  meta.func_id == special_kfunc_list[KF_bpf_timer_set_sleepable_cb_impl]

In case if some new async callback calling kfunc would be added,
for which set_timer_callback_state() won't be correct.

> +		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);
>  
>
diff mbox series

Patch

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);