From: Jiri Olsa <jolsa@redhat.com>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>, Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
Martin KaFai Lau <kafai@fb.com>, David Miller <davem@redhat.com>,
John Fastabend <john.fastabend@gmail.com>,
Wenbo Zhang <ethercflow@gmail.com>,
KP Singh <kpsingh@chromium.org>, Andrii Nakryiko <andriin@fb.com>,
Brendan Gregg <bgregg@netflix.com>,
Florent Revest <revest@chromium.org>,
Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH v4 bpf-next 07/14] bpf: Allow nested BTF object to be refferenced by BTF object + offset
Date: Tue, 30 Jun 2020 15:54:49 +0200 [thread overview]
Message-ID: <20200630135449.GA3071036@krava> (raw)
In-Reply-To: <CAEf4Bzb+Oey2pQMJvBpRR6dVqFDeV+OtyQVoCvk-1rmvb6XYPA@mail.gmail.com>
On Mon, Jun 29, 2020 at 06:52:21PM -0700, Andrii Nakryiko wrote:
> On Thu, Jun 25, 2020 at 4:49 PM Jiri Olsa <jolsa@kernel.org> wrote:
> >
> > Adding btf_struct_address function that takes 2 BTF objects
> > and offset as arguments and checks whether object A is nested
> > in object B on given offset.
> >
> > This function will be used when checking the helper function
> > PTR_TO_BTF_ID arguments. If the argument has an offset value,
> > the btf_struct_address will check if the final address is
> > the expected BTF ID.
> >
> > This way we can access nested BTF objects under PTR_TO_BTF_ID
> > pointer type and pass them to helpers, while they still point
> > to valid kernel BTF objects.
> >
> > Using btf_struct_access to implement new btf_struct_address
> > function, because it already walks down the given BTF object.
> >
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > ---
>
> This logic is very hard to follow. Each type I try to review it, I get
> lost very fast. TBH, this access_data struct is not just not helpful,
> but actually just complicates everything.
yea, it's one of the reasons I added extra function for that in first version
>
> I'll get to this tomorrow morning with fresh brains and will try to do
> another pass.
>
> [...]
>
> > int btf_resolve_helper_id(struct bpf_verifier_log *log,
> > const struct bpf_func_proto *fn, int arg)
> > {
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index 7de98906ddf4..da7351184295 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -3808,6 +3808,7 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
> > struct bpf_reg_state *regs = cur_regs(env), *reg = ®s[regno];
> > enum bpf_reg_type expected_type, type = reg->type;
> > enum bpf_arg_type arg_type = fn->arg_type[arg];
> > + const struct btf_type *btf_type;
> > int err = 0;
> >
> > if (arg_type == ARG_DONTCARE)
> > @@ -3887,24 +3888,34 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
> > expected_type = PTR_TO_BTF_ID;
> > if (type != expected_type)
> > goto err_type;
> > - if (!fn->check_btf_id) {
> > - if (reg->btf_id != meta->btf_id) {
> > - verbose(env, "Helper has type %s got %s in R%d\n",
> > + if (reg->off) {
>
>
> This non-zero offset only logic looks fishy, tbh. What if the struct
> you are trying to access is at offset zero? E.g., bpf_link is pretty
> much always a first field of whatever specific link struct it is
> contained within. The fact that we allow only non-zero offsets for
> such use case looks like an arbitrary limitation.
right, that's mistake, I was after path under struct file,
and did not realize this needs to be generic
thanks,
jirka
>
> > + btf_type = btf_type_by_id(btf_vmlinux, reg->btf_id);
> > + if (btf_struct_address(&env->log, btf_type, reg->off, meta->btf_id)) {
> > + verbose(env, "Helper has type %s got %s in R%d, off %d\n",
> > kernel_type_name(meta->btf_id),
> > + kernel_type_name(reg->btf_id), regno, reg->off);
> > + return -EACCES;
> > + }
>
> [...]
>
next prev parent reply other threads:[~2020-06-30 13:55 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-25 22:12 [PATCH v4 bpf-next 00/14] bpf: Add d_path helper Jiri Olsa
2020-06-25 22:12 ` [PATCH v4 bpf-next 01/14] bpf: Add resolve_btfids tool to resolve BTF IDs in ELF object Jiri Olsa
2020-06-26 20:53 ` Andrii Nakryiko
2020-06-26 21:09 ` Yonghong Song
2020-06-28 19:09 ` Alexei Starovoitov
2020-06-28 19:35 ` Jiri Olsa
2020-06-28 20:53 ` Yonghong Song
2020-06-25 22:12 ` [PATCH v4 bpf-next 02/14] bpf: Compile resolve_btfids tool at kernel compilation start Jiri Olsa
2020-06-26 21:28 ` Andrii Nakryiko
2020-06-28 19:48 ` Jiri Olsa
2020-06-25 22:12 ` [PATCH v4 bpf-next 03/14] bpf: Add BTF_ID_LIST/BTF_ID macros Jiri Olsa
2020-06-26 21:32 ` Andrii Nakryiko
2020-06-28 19:50 ` Jiri Olsa
2020-06-25 22:12 ` [PATCH v4 bpf-next 04/14] bpf: Resolve BTF IDs in vmlinux image Jiri Olsa
2020-06-26 21:34 ` Andrii Nakryiko
2020-06-25 22:12 ` [PATCH v4 bpf-next 05/14] bpf: Remove btf_id helpers resolving Jiri Olsa
2020-06-26 21:36 ` Yonghong Song
2020-06-26 21:40 ` Andrii Nakryiko
2020-06-26 23:29 ` Yonghong Song
2020-06-28 18:50 ` Alexei Starovoitov
2020-06-28 20:00 ` Andrii Nakryiko
2020-06-28 20:16 ` Jiri Olsa
2020-06-28 20:59 ` Yonghong Song
2020-06-28 21:20 ` Jiri Olsa
2020-06-25 22:12 ` [PATCH v4 bpf-next 06/14] bpf: Use BTF_ID to resolve bpf_ctx_convert struct Jiri Olsa
2020-06-26 21:44 ` Andrii Nakryiko
2020-06-26 21:44 ` Yonghong Song
2020-06-28 19:52 ` Jiri Olsa
2020-06-25 22:12 ` [PATCH v4 bpf-next 07/14] bpf: Allow nested BTF object to be refferenced by BTF object + offset Jiri Olsa
2020-06-30 1:52 ` Andrii Nakryiko
2020-06-30 13:54 ` Jiri Olsa [this message]
2020-06-30 20:05 ` Andrii Nakryiko
2020-06-30 20:07 ` Andrii Nakryiko
2020-07-02 10:08 ` Jiri Olsa
2020-07-06 23:15 ` Andrii Nakryiko
2020-06-25 22:12 ` [PATCH v4 bpf-next 08/14] bpf: Add BTF_SET_START/END macros Jiri Olsa
2020-06-26 21:49 ` Andrii Nakryiko
2020-06-25 22:12 ` [PATCH v4 bpf-next 09/14] bpf: Add info about .BTF.ids section to btf.rst Jiri Olsa
2020-06-25 22:13 ` [PATCH v4 bpf-next 10/14] bpf: Add d_path helper Jiri Olsa
2020-06-26 20:38 ` Andrii Nakryiko
2020-06-28 19:42 ` Jiri Olsa
2020-07-16 23:13 ` KP Singh
2020-07-17 8:28 ` Jiri Olsa
2020-06-25 22:13 ` [PATCH v4 bpf-next 11/14] tools headers: Adopt verbatim copy of btf_ids.h from kernel sources Jiri Olsa
2020-06-26 21:51 ` Andrii Nakryiko
2020-06-25 22:13 ` [PATCH v4 bpf-next 12/14] selftests/bpf: Add verifier test for d_path helper Jiri Olsa
2020-06-30 1:30 ` Andrii Nakryiko
2020-06-25 22:13 ` [PATCH v4 bpf-next 13/14] selftests/bpf: Add " Jiri Olsa
2020-06-26 21:55 ` Andrii Nakryiko
2020-06-28 19:55 ` Jiri Olsa
2020-06-25 22:13 ` [PATCH v4 bpf-next 14/14] selftests/bpf: Add test for resolve_btfids Jiri Olsa
2020-06-30 1:43 ` Andrii Nakryiko
2020-06-30 14:27 ` Jiri Olsa
2020-06-30 18:13 ` Andrii Nakryiko
2020-06-30 1:54 ` [PATCH v4 bpf-next 00/14] bpf: Add d_path helper Andrii Nakryiko
2020-06-30 13:55 ` Jiri Olsa
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