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@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";

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