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From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Andrii Nakryiko <andriin@fb.com>, bpf <bpf@vger.kernel.org>,
	Networking <netdev@vger.kernel.org>,
	Alexei Starovoitov <ast@fb.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Kernel Team <kernel-team@fb.com>,
	"Paul E . McKenney" <paulmck@kernel.org>,
	Jonathan Lemon <jonathan.lemon@gmail.com>
Subject: Re: [PATCH v2 bpf-next 1/7] bpf: implement BPF ring buffer and verifier support for it
Date: Fri, 22 May 2020 11:48:09 -0700
Message-ID: <CAEf4BzZLYtgZg8caSpMkFf4-NJXQHbiTXhwnY7wnq7qDbgA9Gw@mail.gmail.com> (raw)
In-Reply-To: <20200522010722.2lgagrt6cmw6dzmm@ast-mbp.dhcp.thefacebook.com>

On Thu, May 21, 2020 at 6:07 PM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Sun, May 17, 2020 at 12:57:21PM -0700, Andrii Nakryiko wrote:
> > -     if (off < 0 || size < 0 || (size == 0 && !zero_size_allowed) ||
> > -         off + size > map->value_size) {
> > -             verbose(env, "invalid access to map value, value_size=%d off=%d size=%d\n",
> > -                     map->value_size, off, size);
> > -             return -EACCES;
> > -     }
> > -     return 0;
> > +     if (off >= 0 && size_ok && off + size <= mem_size)
> > +             return 0;
> > +
> > +     verbose(env, "invalid access to memory, mem_size=%u off=%d size=%d\n",
> > +             mem_size, off, size);
> > +     return -EACCES;
>
> iirc invalid access to map value is one of most common verifier errors that
> people see when they're use unbounded access. Generalizing it to memory is
> technically correct, but it makes the message harder to decipher.
> What is 'mem_size' ? Without context it is difficult to guess that
> it's actually size of map value element.
> Could you make this error message more human friendly depending on
> type of pointer?

yep, sure, better verifier errors are extremely important, I think

>
> >       if (err) {
> > -             verbose(env, "R%d min value is outside of the array range\n",
> > +             verbose(env, "R%d min value is outside of the memory region\n",
> >                       regno);
> >               return err;
> >       }
> > @@ -2518,18 +2527,38 @@ static int check_map_access(struct bpf_verifier_env *env, u32 regno,
> >        * If reg->umax_value + off could overflow, treat that as unbounded too.
> >        */
> >       if (reg->umax_value >= BPF_MAX_VAR_OFF) {
> > -             verbose(env, "R%d unbounded memory access, make sure to bounds check any array access into a map\n",
> > +             verbose(env, "R%d unbounded memory access, make sure to bounds check any memory region access\n",
> >                       regno);
> >               return -EACCES;
> >       }
> > -     err = __check_map_access(env, regno, reg->umax_value + off, size,
> > +     err = __check_mem_access(env, reg->umax_value + off, size, mem_size,
> >                                zero_size_allowed);
> > -     if (err)
> > -             verbose(env, "R%d max value is outside of the array range\n",
> > +     if (err) {
> > +             verbose(env, "R%d max value is outside of the memory region\n",
> >                       regno);
>
> I'm not that worried about above three generalizations of errors,
> but if you can make it friendly by describing type of memory region
> I think it will be a plus.

I agree, will update

  reply index

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-17 19:57 [PATCH v2 bpf-next 0/7] BPF ring buffer Andrii Nakryiko
2020-05-17 19:57 ` [PATCH v2 bpf-next 1/7] bpf: implement BPF ring buffer and verifier support for it Andrii Nakryiko
2020-05-19 12:57   ` kbuild test robot
2020-05-19 23:53   ` kbuild test robot
2020-05-22  0:25   ` Paul E. McKenney
2020-05-22 18:46     ` Andrii Nakryiko
2020-05-25 16:01       ` Paul E. McKenney
2020-05-25 18:45         ` Andrii Nakryiko
2020-05-22  1:07   ` Alexei Starovoitov
2020-05-22 18:48     ` Andrii Nakryiko [this message]
2020-05-25 20:34     ` Andrii Nakryiko
2020-05-17 19:57 ` [PATCH v2 bpf-next 2/7] tools/memory-model: add BPF ringbuf MPSC litmus tests Andrii Nakryiko
2020-05-22  0:34   ` Paul E. McKenney
2020-05-22 18:51     ` Andrii Nakryiko
2020-05-25 23:33       ` Andrii Nakryiko
2020-05-26  3:05         ` Paul E. McKenney
2020-05-17 19:57 ` [PATCH v2 bpf-next 3/7] bpf: track reference type in verifier Andrii Nakryiko
2020-05-22  1:13   ` Alexei Starovoitov
2020-05-22 18:53     ` Andrii Nakryiko
2020-05-17 19:57 ` [PATCH v2 bpf-next 4/7] libbpf: add BPF ring buffer support Andrii Nakryiko
2020-05-22  1:15   ` Alexei Starovoitov
2020-05-22 18:56     ` Andrii Nakryiko
2020-05-17 19:57 ` [PATCH v2 bpf-next 5/7] selftests/bpf: add BPF ringbuf selftests Andrii Nakryiko
2020-05-22  1:20   ` Alexei Starovoitov
2020-05-22 18:58     ` Andrii Nakryiko
2020-05-17 19:57 ` [PATCH v2 bpf-next 6/7] bpf: add BPF ringbuf and perf buffer benchmarks Andrii Nakryiko
2020-05-22  1:21   ` Alexei Starovoitov
2020-05-22 19:07     ` Andrii Nakryiko
2020-05-17 19:57 ` [PATCH v2 bpf-next 7/7] docs/bpf: add BPF ring buffer design notes Andrii Nakryiko
2020-05-22  1:23   ` Alexei Starovoitov
2020-05-22 19:08     ` Andrii Nakryiko
2020-05-25  9:59   ` Alban Crequy
2020-05-25 19:12     ` Andrii Nakryiko

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