On Wed, Feb 21, 2024 at 8:25 AM Benjamin Tissoires <bentiss@xxxxxxxxxx> 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@xxxxxxxxxx>
>
> ---
>
> 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.
