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

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Date: Mon, 18 Mar 2024 23:53:39 +0200
From: Eduard Zingerman <eddyz87@...il.com>
To: 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>
Cc: 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 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:

--- 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";

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