From: Daniel Borkmann <daniel@iogearbox.net>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>,
Jiri Olsa <jolsa@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andriin@fb.com>,
Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
Yonghong Song <yhs@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@chromium.org>
Subject: Re: [PATCH] bpf: Forbid trampoline attach for functions with variable arguments
Date: Fri, 7 May 2021 01:31:54 +0200 [thread overview]
Message-ID: <c21b54a6-8d6e-f76d-e6c1-95abd8544d9d@iogearbox.net> (raw)
In-Reply-To: <CAEf4BzazQgrPVqKOGP8z=MPZhjZHCZDdcWQB0xBuudXbxXwaXg@mail.gmail.com>
On 5/5/21 8:45 PM, Andrii Nakryiko wrote:
> On Wed, May 5, 2021 at 6:42 AM Jiri Olsa <jolsa@kernel.org> wrote:
>>
>> We can't currently allow to attach functions with variable arguments.
>> The problem is that we should save all the registers for arguments,
>> which is probably doable, but if caller uses more than 6 arguments,
>> we need stack data, which will be wrong, because of the extra stack
>> frame we do in bpf trampoline, so we could crash.
>>
>> Also currently there's malformed trampoline code generated for such
>> functions at the moment as described in:
>> https://lore.kernel.org/bpf/20210429212834.82621-1-jolsa@kernel.org/
>>
>> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
>> ---
>
> LGTM.
>
> Acked-by: Andrii Nakryiko <andrii@kernel.org>
>
>> kernel/bpf/btf.c | 13 +++++++++++++
>> 1 file changed, 13 insertions(+)
>>
>> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
>> index 0600ed325fa0..161511bb3e51 100644
>> --- a/kernel/bpf/btf.c
>> +++ b/kernel/bpf/btf.c
>> @@ -5206,6 +5206,13 @@ int btf_distill_func_proto(struct bpf_verifier_log *log,
>> m->ret_size = ret;
>>
>> for (i = 0; i < nargs; i++) {
>> + if (i == nargs - 1 && args[i].type == 0) {
>> + bpf_log(log,
>> + "The function %s with variable args is unsupported.\n",
>> + tname);
>> + return -EINVAL;
>> +
(Jiri, fyi, I removed this extra newline while applying. Please scan for such
things before submitting.)
>> + }
>> ret = __get_type_size(btf, args[i].type, &t);
>> if (ret < 0) {
>> bpf_log(log,
>> @@ -5213,6 +5220,12 @@ int btf_distill_func_proto(struct bpf_verifier_log *log,
>> tname, i, btf_kind_str[BTF_INFO_KIND(t->info)]);
>> return -EINVAL;
>> }
>> + if (ret == 0) {
>> + bpf_log(log,
>> + "The function %s has malformed void argument.\n",
>> + tname);
>> + return -EINVAL;
>> + }
>> m->arg_size[i] = ret;
>> }
>> m->nr_args = nargs;
>> --
>> 2.30.2
>>
next prev parent reply other threads:[~2021-05-06 23:32 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-05 13:25 [PATCH] bpf: Forbid trampoline attach for functions with variable arguments Jiri Olsa
2021-05-05 18:45 ` Andrii Nakryiko
2021-05-06 23:31 ` Daniel Borkmann [this message]
2021-05-07 8:13 ` Jiri Olsa
2021-05-06 23:30 ` patchwork-bot+netdevbpf
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