From: Martin Lau <kafai@fb.com>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: bpf <bpf@vger.kernel.org>, Alexei Starovoitov <ast@kernel.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
David Miller <davem@davemloft.net>,
"Kernel Team" <Kernel-team@fb.com>,
Networking <netdev@vger.kernel.org>
Subject: Re: [PATCH bpf-next v2 05/11] bpf: Introduce BPF_PROG_TYPE_STRUCT_OPS
Date: Mon, 23 Dec 2019 22:29:59 +0000 [thread overview]
Message-ID: <20191223222955.2d2hxboqzgp7662r@kafai-mbp> (raw)
In-Reply-To: <CAEf4BzYF8mBrkzM3=+XtyCwoQrLGvkA-6Uc3KXJ9CWmaKePX8Q@mail.gmail.com>
On Mon, Dec 23, 2019 at 12:29:37PM -0800, Andrii Nakryiko wrote:
> On Fri, Dec 20, 2019 at 10:26 PM Martin KaFai Lau <kafai@fb.com> wrote:
> >
> > This patch allows the kernel's struct ops (i.e. func ptr) to be
> > implemented in BPF. The first use case in this series is the
> > "struct tcp_congestion_ops" which will be introduced in a
> > latter patch.
> >
> > This patch introduces a new prog type BPF_PROG_TYPE_STRUCT_OPS.
> > The BPF_PROG_TYPE_STRUCT_OPS prog is verified against a particular
> > func ptr of a kernel struct. The attr->attach_btf_id is the btf id
> > of a kernel struct. The attr->expected_attach_type is the member
> > "index" of that kernel struct. The first member of a struct starts
> > with member index 0. That will avoid ambiguity when a kernel struct
> > has multiple func ptrs with the same func signature.
> >
> > For example, a BPF_PROG_TYPE_STRUCT_OPS prog is written
> > to implement the "init" func ptr of the "struct tcp_congestion_ops".
> > The attr->attach_btf_id is the btf id of the "struct tcp_congestion_ops"
> > of the _running_ kernel. The attr->expected_attach_type is 3.
> >
> > The ctx of BPF_PROG_TYPE_STRUCT_OPS is an array of u64 args saved
> > by arch_prepare_bpf_trampoline that will be done in the next
> > patch when introducing BPF_MAP_TYPE_STRUCT_OPS.
> >
> > "struct bpf_struct_ops" is introduced as a common interface for the kernel
> > struct that supports BPF_PROG_TYPE_STRUCT_OPS prog. The supporting kernel
> > struct will need to implement an instance of the "struct bpf_struct_ops".
> >
> > The supporting kernel struct also needs to implement a bpf_verifier_ops.
> > During BPF_PROG_LOAD, bpf_struct_ops_find() will find the right
> > bpf_verifier_ops by searching the attr->attach_btf_id.
> >
> > A new "btf_struct_access" is also added to the bpf_verifier_ops such
> > that the supporting kernel struct can optionally provide its own specific
> > check on accessing the func arg (e.g. provide limited write access).
> >
> > After btf_vmlinux is parsed, the new bpf_struct_ops_init() is called
> > to initialize some values (e.g. the btf id of the supporting kernel
> > struct) and it can only be done once the btf_vmlinux is available.
> >
> > The R0 checks at BPF_EXIT is excluded for the BPF_PROG_TYPE_STRUCT_OPS prog
> > if the return type of the prog->aux->attach_func_proto is "void".
> >
> > Signed-off-by: Martin KaFai Lau <kafai@fb.com>
> > ---
> > include/linux/bpf.h | 30 +++++++
> > include/linux/bpf_types.h | 4 +
> > include/linux/btf.h | 34 ++++++++
> > include/uapi/linux/bpf.h | 1 +
> > kernel/bpf/Makefile | 2 +-
> > kernel/bpf/bpf_struct_ops.c | 122 +++++++++++++++++++++++++++
> > kernel/bpf/bpf_struct_ops_types.h | 4 +
> > kernel/bpf/btf.c | 88 ++++++++++++++------
> > kernel/bpf/syscall.c | 17 ++--
> > kernel/bpf/verifier.c | 134 +++++++++++++++++++++++-------
> > 10 files changed, 372 insertions(+), 64 deletions(-)
> > create mode 100644 kernel/bpf/bpf_struct_ops.c
> > create mode 100644 kernel/bpf/bpf_struct_ops_types.h
> >
>
> All looks good, apart from the concern with partially-initialized
> bpf_struct_ops.
>
> [...]
>
> > +const struct bpf_prog_ops bpf_struct_ops_prog_ops = {
> > +};
> > +
> > +void bpf_struct_ops_init(struct btf *_btf_vmlinux)
>
> this is always get passed vmlinux's btf, so why not call it short and
> sweet "btf"? _btf_vmlinux is kind of ugly and verbose.
>
> > +{
> > + const struct btf_member *member;
> > + struct bpf_struct_ops *st_ops;
> > + struct bpf_verifier_log log = {};
> > + const struct btf_type *t;
> > + const char *mname;
> > + s32 type_id;
> > + u32 i, j;
> > +
>
> [...]
>
> > +static int check_struct_ops_btf_id(struct bpf_verifier_env *env)
> > +{
> > + const struct btf_type *t, *func_proto;
> > + const struct bpf_struct_ops *st_ops;
> > + const struct btf_member *member;
> > + struct bpf_prog *prog = env->prog;
> > + u32 btf_id, member_idx;
> > + const char *mname;
> > +
> > + btf_id = prog->aux->attach_btf_id;
> > + st_ops = bpf_struct_ops_find(btf_id);
>
> if struct_ops initialization fails, type will be NULL and type_id will
> be 0, which we rely on here to not get partially-initialized
> bpf_struct_ops, right? Small comment mentioning this would be helpful.
>
>
> > + if (!st_ops) {
> > + verbose(env, "attach_btf_id %u is not a supported struct\n",
> > + btf_id);
> > + return -ENOTSUPP;
> > + }
> > +
>
> [...]
>
> > static int check_attach_btf_id(struct bpf_verifier_env *env)
> > {
> > struct bpf_prog *prog = env->prog;
> > @@ -9520,6 +9591,9 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
> > long addr;
> > u64 key;
> >
> > + if (prog->type == BPF_PROG_TYPE_STRUCT_OPS)
> > + return check_struct_ops_btf_id(env);
> > +
>
> There is a btf_id == 0 check below, you need to check that for
> STRUCT_OPS as well, otherwise you can get partially-initialized
> bpf_struct_ops struct in check_struct_ops_btf_id.
This btf_id == 0 check is done at the beginning of bpf_struct_ops_find().
Hence, bpf_struct_ops_find() won't try to search if btf_id is 0.
st_ops fields is only set when everything passed, so individual st_ops
will not be partially initialized.
>
> > if (prog->type != BPF_PROG_TYPE_TRACING)
> > return 0;
> >
> > --
> > 2.17.1
> >
next prev parent reply other threads:[~2019-12-23 22:30 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-21 6:25 [PATCH bpf-next v2 00/11] Introduce BPF STRUCT_OPS Martin KaFai Lau
2019-12-21 6:25 ` [PATCH bpf-next v2 01/11] bpf: Save PTR_TO_BTF_ID register state when spilling to stack Martin KaFai Lau
2019-12-21 6:25 ` [PATCH bpf-next v2 02/11] bpf: Avoid storing modifier to info->btf_id Martin KaFai Lau
2019-12-21 6:26 ` [PATCH bpf-next v2 03/11] bpf: Add enum support to btf_ctx_access() Martin KaFai Lau
2019-12-21 6:26 ` [PATCH bpf-next v2 04/11] bpf: Support bitfield read access in btf_struct_access Martin KaFai Lau
2019-12-23 7:49 ` Yonghong Song
2019-12-23 20:05 ` Andrii Nakryiko
2019-12-23 21:21 ` Yonghong Song
2019-12-21 6:26 ` [PATCH bpf-next v2 05/11] bpf: Introduce BPF_PROG_TYPE_STRUCT_OPS Martin KaFai Lau
2019-12-23 19:33 ` Yonghong Song
2019-12-23 20:29 ` Andrii Nakryiko
2019-12-23 22:29 ` Martin Lau [this message]
2019-12-23 22:55 ` Andrii Nakryiko
2019-12-24 11:46 ` kbuild test robot
2019-12-21 6:26 ` [PATCH bpf-next v2 06/11] bpf: Introduce BPF_MAP_TYPE_STRUCT_OPS Martin KaFai Lau
2019-12-23 19:57 ` Yonghong Song
2019-12-23 21:44 ` Andrii Nakryiko
2019-12-23 22:15 ` Martin Lau
2019-12-27 6:16 ` Martin Lau
2019-12-23 23:05 ` Andrii Nakryiko
2019-12-28 1:47 ` Martin Lau
2019-12-28 2:24 ` Andrii Nakryiko
2019-12-28 5:16 ` Martin Lau
2019-12-24 12:28 ` kbuild test robot
2019-12-21 6:26 ` [PATCH bpf-next v2 07/11] bpf: tcp: Support tcp_congestion_ops in bpf Martin KaFai Lau
2019-12-23 20:18 ` Yonghong Song
2019-12-23 23:20 ` Andrii Nakryiko
2019-12-24 7:16 ` kbuild test robot
2019-12-24 13:06 ` kbuild test robot
2019-12-21 6:26 ` [PATCH bpf-next v2 08/11] bpf: Add BPF_FUNC_tcp_send_ack helper Martin KaFai Lau
2019-12-21 6:26 ` [PATCH bpf-next v2 09/11] bpf: Synch uapi bpf.h to tools/ Martin KaFai Lau
2019-12-21 6:26 ` [PATCH bpf-next v2 10/11] bpf: libbpf: Add STRUCT_OPS support Martin KaFai Lau
2019-12-23 19:54 ` Andrii Nakryiko
2019-12-26 22:47 ` Martin Lau
2019-12-21 6:26 ` [PATCH bpf-next v2 11/11] bpf: Add bpf_dctcp example Martin KaFai Lau
2019-12-23 23:26 ` Andrii Nakryiko
2019-12-24 1:31 ` Martin Lau
2019-12-24 7:01 ` Andrii Nakryiko
2019-12-24 7:32 ` Martin Lau
2019-12-24 16:50 ` Martin Lau
2019-12-26 19:02 ` Andrii Nakryiko
2019-12-26 20:25 ` Martin Lau
2019-12-26 20:48 ` Andrii Nakryiko
2019-12-26 22:20 ` Martin Lau
2019-12-26 22:25 ` Andrii Nakryiko
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20191223222955.2d2hxboqzgp7662r@kafai-mbp \
--to=kafai@fb.com \
--cc=Kernel-team@fb.com \
--cc=andrii.nakryiko@gmail.com \
--cc=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=daniel@iogearbox.net \
--cc=davem@davemloft.net \
--cc=netdev@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).