Re: [PATCH bpf-next v4 2/6] bpf/verifier: add bpf_timer as a kfunc capable type

[Benjamin Tissoires <benjamin.tissoires@redhat.com>]

On Mon, Mar 18, 2024 at 10:59 PM Eduard Zingerman <eddyz87@gmail.com> wrote:
>
> On Fri, 2024-03-15 at 15:29 +0100, Benjamin Tissoires wrote:
> [...]
>
> > @@ -12021,6 +12034,12 @@ 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:
> > +                     if (reg->type != PTR_TO_MAP_VALUE) {
> > +                             verbose(env, "arg#%d doesn't point to a map value\n", i);
> > +                             return -EINVAL;
> > +                     }
> > +                     break;
>
> I think that pointer offset has to be checked as well,
> otherwise the following program verifies w/o error:

I initially thought it would be harder than it actually was.

Fixed (with the new test below) in v5.

Cheers,
Benjamin

>
> --- 8< ----------------------------
>
> #include <linux/bpf.h>
> #include <time.h>
> #include <errno.h>
> #include <bpf/bpf_helpers.h>
> #include "bpf_tcp_helpers.h"
>
> extern int bpf_timer_set_sleepable_cb_impl(struct bpf_timer *timer,
>                 int (callback_fn)(void *map, int *key, struct bpf_timer *timer), void *aux__ign) __ksym;
>
> #define bpf_timer_set_sleepable_cb(timer, cb) \
>         bpf_timer_set_sleepable_cb_impl(timer, cb, NULL)
>
> struct elem {
>         struct bpf_timer t;
> };
>
> struct {
>         __uint(type, BPF_MAP_TYPE_ARRAY);
>         __uint(max_entries, 2);
>         __type(key, int);
>         __type(value, struct elem);
> } array SEC(".maps");
>
> static int cb_sleepable(void *map, int *key, struct bpf_timer *timer)
> {
>         return 0;
> }
>
> SEC("fentry/bpf_fentry_test5")
> int BPF_PROG2(test_sleepable, int, a)
> {
>         struct bpf_timer *arr_timer;
>         int array_key = 1;
>
>         arr_timer = bpf_map_lookup_elem(&array, &array_key);
>         if (!arr_timer)
>                 return 0;
>         bpf_timer_init(arr_timer, &array, CLOCK_MONOTONIC);
>         bpf_timer_set_sleepable_cb((void *)arr_timer + 1, // <-- note incorrect offset
>                                    cb_sleepable);
>         bpf_timer_start(arr_timer, 0, 0);
>         return 0;
> }
>
> char _license[] SEC("license") = "GPL";
>
> ---------------------------- >8 ---
>