From: Jiri Olsa <jolsa@redhat.com>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>,
Jiri Olsa <jolsa@kernel.org>, Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
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 RFC] bpf: Fix trampoline for functions with variable arguments
Date: Wed, 5 May 2021 14:42:47 +0200 [thread overview]
Message-ID: <YJKSx9qLB432dCWs@krava> (raw)
In-Reply-To: <CAADnVQ+V=2qOqkVMaC72uhQKEbC=2uFa80J57xdF_4ffoZHYNQ@mail.gmail.com>
On Tue, May 04, 2021 at 09:11:26PM -0700, Alexei Starovoitov wrote:
SNIP
> > > > >
> > > > > actualy looks like we need to disable functions with variable arguments
> > > > > completely, because we don't know how many arguments to save
> > > > >
> > > > > I tried to disable them in pahole and it's easy fix, will post new fix
> > > >
> > > > Can we still allow access to fixed arguments for such functions and
> > > > just disallow the vararg ones?
> > >
> > > 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
> > >
> > > the patch below prevents to attach these functions directly in kernel,
> > > so we could keep these functions in BTF
> > >
> > > jirka
> > >
> > >
> > > ---
> > > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> > > index 0600ed325fa0..f9709dc08c44 100644
> > > --- a/kernel/bpf/btf.c
> > > +++ b/kernel/bpf/btf.c
> > > @@ -5213,6 +5213,13 @@ 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 variable args, it's unsupported.\n",
> > > + tname);
> > > + return -EINVAL;
> > > +
> > > + }
> >
> > this will work, but the explicit check for vararg should be `i ==
> > nargs - 1 && args[i].type == 0`. Everything else (if it happens) is
> > probably a bad BTF data.
>
> Jiri,
> could you please resubmit with the check like Andrii suggested?
> Thanks!
>
yes, will send it later today
jirka
prev parent reply other threads:[~2021-05-05 12:42 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-29 21:28 [PATCH RFC] bpf: Fix trampoline for functions with variable arguments Jiri Olsa
2021-05-02 21:16 ` Jiri Olsa
2021-05-03 22:32 ` Andrii Nakryiko
2021-05-04 13:27 ` Jiri Olsa
2021-05-04 22:37 ` Andrii Nakryiko
2021-05-05 4:11 ` Alexei Starovoitov
2021-05-05 12:42 ` Jiri Olsa [this message]
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