linux-kernel - Re: [PATCH bpf-next v4 2/6] bpf/verifier: add bpf

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Date: Thu, 21 Mar 2024 16:58:38 +0100
From: Benjamin Tissoires <benjamin.tissoires@...hat.com>
To: Eduard Zingerman <eddyz87@...il.com>
Cc: Benjamin Tissoires <bentiss@...nel.org>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>, 
	bpf@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-kselftest@...r.kernel.org
Subject: Re: [PATCH bpf-next v4 2/6] bpf/verifier: add bpf_timer as a kfunc
 capable type

On Mon, Mar 18, 2024 at 10:59 PM Eduard Zingerman <eddyz87@...il.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 ---
>