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From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: Daniel Borkmann <daniel@iogearbox.net>
Cc: Alexei Starovoitov <ast@kernel.org>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>,
	Marek Majkowski <marek@cloudflare.com>,
	Lorenz Bauer <lmb@cloudflare.com>,
	Alan Maguire <alan.maguire@oracle.com>,
	Jesper Dangaard Brouer <brouer@redhat.com>,
	David Miller <davem@davemloft.net>,
	netdev@vger.kernel.org, bpf@vger.kernel.org
Subject: Re: [PATCH bpf-next v3 2/5] bpf: Add support for setting chain call sequence for programs
Date: Tue, 08 Oct 2019 10:09:34 +0200	[thread overview]
Message-ID: <87pnj7lku9.fsf@toke.dk> (raw)
In-Reply-To: <20191007203855.GE27307@pc-66.home>

Daniel Borkmann <daniel@iogearbox.net> writes:

> On Mon, Oct 07, 2019 at 07:20:37PM +0200, Toke Høiland-Jørgensen wrote:
>> From: Toke Høiland-Jørgensen <toke@redhat.com>
>> 
>> This adds support for setting and deleting bpf chain call programs through
>> a couple of new commands in the bpf() syscall. The CHAIN_ADD and CHAIN_DEL
>> commands take two eBPF program fds and a return code, and install the
>> 'next' program to be chain called after the 'prev' program if that program
>> returns 'retcode'. A retcode of -1 means "wildcard", so that the program
>> will be executed regardless of the previous program's return code.
>> 
>> 
>> The syscall command names are based on Alexei's prog_chain example[0],
>> which Alan helpfully rebased on current bpf-next. However, the logic and
>> program storage is obviously adapted to the execution logic in the previous
>> commit.
>> 
>> [0] https://git.kernel.org/pub/scm/linux/kernel/git/ast/bpf.git/commit/?h=prog_chain&id=f54f45d00f91e083f6aec2abe35b6f0be52ae85b&context=15
>> 
>> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
>> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
>> ---
>>  include/uapi/linux/bpf.h |   10 ++++++
>>  kernel/bpf/syscall.c     |   78 ++++++++++++++++++++++++++++++++++++++++++++++
>>  2 files changed, 88 insertions(+)
>> 
>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
>> index 1ce80a227be3..b03c23963af8 100644
>> --- a/include/uapi/linux/bpf.h
>> +++ b/include/uapi/linux/bpf.h
>> @@ -107,6 +107,9 @@ enum bpf_cmd {
>>  	BPF_MAP_LOOKUP_AND_DELETE_ELEM,
>>  	BPF_MAP_FREEZE,
>>  	BPF_BTF_GET_NEXT_ID,
>> +	BPF_PROG_CHAIN_ADD,
>> +	BPF_PROG_CHAIN_DEL,
>> +	BPF_PROG_CHAIN_GET,
>>  };
>>  
>>  enum bpf_map_type {
>> @@ -516,6 +519,13 @@ union bpf_attr {
>>  		__u64		probe_offset;	/* output: probe_offset */
>>  		__u64		probe_addr;	/* output: probe_addr */
>>  	} task_fd_query;
>> +
>> +	struct { /* anonymous struct used by BPF_PROG_CHAIN_* commands */
>> +		__u32		prev_prog_fd;
>> +		__u32		next_prog_fd;
>> +		__u32		retcode;
>> +		__u32		next_prog_id;   /* output: prog_id */
>> +	};
>>  } __attribute__((aligned(8)));
>>  
>>  /* The description below is an attempt at providing documentation to eBPF
>> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
>> index b8a203a05881..be8112e08a88 100644
>> --- a/kernel/bpf/syscall.c
>> +++ b/kernel/bpf/syscall.c
>> @@ -2113,6 +2113,79 @@ static int bpf_prog_test_run(const union bpf_attr *attr,
>>  	return ret;
>>  }
>>  
>> +#define BPF_PROG_CHAIN_LAST_FIELD next_prog_id
>> +
>> +static int bpf_prog_chain(int cmd, const union bpf_attr *attr,
>> +			  union bpf_attr __user *uattr)
>> +{
>> +	struct bpf_prog *prog, *next_prog, *old_prog;
>> +	struct bpf_prog **array;
>> +	int ret = -EOPNOTSUPP;
>> +	u32 index, prog_id;
>> +
>> +	if (CHECK_ATTR(BPF_PROG_CHAIN))
>> +		return -EINVAL;
>> +
>> +	/* Index 0 is wildcard, encoded as ~0 by userspace */
>> +	if (attr->retcode == ((u32) ~0))
>> +		index = 0;
>> +	else
>> +		index = attr->retcode + 1;
>> +
>> +	if (index >= BPF_NUM_CHAIN_SLOTS)
>> +		return -E2BIG;
>> +
>> +	prog = bpf_prog_get(attr->prev_prog_fd);
>> +	if (IS_ERR(prog))
>> +		return PTR_ERR(prog);
>> +
>> +	/* If the chain_calls bit is not set, that's because the chain call flag
>> +	 * was not set on program load, and so we can't support chain calls.
>> +	 */
>> +	if (!prog->chain_calls)
>> +		goto out;
>> +
>> +	array = prog->aux->chain_progs;
>> +
>> +	switch (cmd) {
>> +	case BPF_PROG_CHAIN_ADD:
>> +		next_prog = bpf_prog_get(attr->next_prog_fd);
>> +		if (IS_ERR(next_prog)) {
>> +			ret = PTR_ERR(next_prog);
>> +			break;
>> +		}
>> +		old_prog = xchg(array + index, next_prog);
>> +		if (old_prog)
>> +			bpf_prog_put(old_prog);
>> +		ret = 0;
>> +		break;
>
> How are circular dependencies resolved here? Seems the situation is
> not prevented, so progs unloaded via XDP won't get the __bpf_prog_free()
> call where they then drop the references of all the other progs in the
> chain.

Yeah, that's true. My plan was to just walk the "call graph" on insert
and reject any circular inserts. Just haven't gotten around to adding
that yet; will fix that in the next version.

-Toke

  reply	other threads:[~2019-10-08  8:09 UTC|newest]

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-07 17:20 [PATCH bpf-next v3 0/5] xdp: Support multiple programs on a single interface through chain calls Toke Høiland-Jørgensen
2019-10-07 17:20 ` [PATCH bpf-next v3 1/5] bpf: Support chain calling multiple BPF programs after each other Toke Høiland-Jørgensen
2019-10-07 20:42   ` Alexei Starovoitov
2019-10-08  8:07     ` Toke Høiland-Jørgensen
2019-10-09  1:51       ` Alexei Starovoitov
2019-10-09  8:03         ` Toke Høiland-Jørgensen
2019-10-10  4:41           ` Alexei Starovoitov
2019-10-14 12:35             ` Toke Høiland-Jørgensen
2019-10-14 17:08               ` John Fastabend
2019-10-14 18:48                 ` Toke Høiland-Jørgensen
2019-10-15 16:30                   ` Edward Cree
2019-10-15 16:42                     ` Toke Høiland-Jørgensen
2019-10-15 18:33                       ` Edward Cree
2019-10-17 12:11                         ` Toke Høiland-Jørgensen
2019-10-22 17:27                           ` Edward Cree
2019-10-22 18:07                             ` Toke Høiland-Jørgensen
2019-11-12  2:51                               ` static and dynamic linking. Was: [PATCH bpf-next v3 1/5] bpf: Support chain calling multiple BPF Alexei Starovoitov
2019-11-12 16:20                                 ` Toke Høiland-Jørgensen
2019-11-12 19:52                                   ` Alexei Starovoitov
2019-11-12 21:25                                     ` Edward Cree
2019-11-12 23:18                                       ` Alexei Starovoitov
2019-11-13 18:30                                         ` Edward Cree
2019-11-13 18:51                                           ` Andrii Nakryiko
2019-11-15  2:13                                           ` Alexei Starovoitov
2019-11-15 16:56                                             ` John Fastabend
2019-11-12 23:25                                     ` John Fastabend
2019-11-13  0:21                                       ` Alexei Starovoitov
2019-11-13  5:33                                         ` John Fastabend
2019-11-15  1:50                                           ` Alexei Starovoitov
2019-11-15 16:39                                             ` John Fastabend
2019-11-14 15:41                                     ` Toke Høiland-Jørgensen
2019-11-12 16:32                                 ` Edward Cree
2019-11-15 11:48                                 ` Lorenz Bauer
2019-11-15 23:02                                   ` Alexei Starovoitov
2019-11-18 13:29                                     ` Lorenz Bauer
2019-10-21 23:51                         ` [PATCH bpf-next v3 1/5] bpf: Support chain calling multiple BPF programs after each other Edward Cree
2019-10-16  2:28               ` Alexei Starovoitov
2019-10-16  8:27                 ` Jesper Dangaard Brouer
2019-10-16 10:35                   ` Daniel Borkmann
2019-10-16 11:16                     ` Toke Høiland-Jørgensen
2019-10-16 13:51                 ` Toke Høiland-Jørgensen
2019-10-19 20:09                   ` bpf indirect calls Alexei Starovoitov
2019-10-20 10:58                     ` Toke Høiland-Jørgensen
2019-10-25 16:30                       ` Alexei Starovoitov
2019-10-27 12:15                         ` Toke Høiland-Jørgensen
2019-10-09 10:19         ` [PATCH bpf-next v3 1/5] bpf: Support chain calling multiple BPF programs after each other Jesper Dangaard Brouer
2019-10-09 17:57           ` Alexei Starovoitov
2019-10-07 17:20 ` [PATCH bpf-next v3 2/5] bpf: Add support for setting chain call sequence for programs Toke Høiland-Jørgensen
2019-10-07 20:38   ` Daniel Borkmann
2019-10-08  8:09     ` Toke Høiland-Jørgensen [this message]
2019-10-07 17:20 ` [PATCH bpf-next v3 3/5] tools: Update bpf.h header for program chain calls Toke Høiland-Jørgensen
2019-10-07 17:20 ` [PATCH bpf-next v3 4/5] libbpf: Add syscall wrappers for BPF_PROG_CHAIN_* commands Toke Høiland-Jørgensen
2019-10-07 17:20 ` [PATCH bpf-next v3 5/5] selftests: Add tests for XDP chain calls Toke Høiland-Jørgensen
2019-10-07 18:58 ` [PATCH bpf-next v3 0/5] xdp: Support multiple programs on a single interface through " John Fastabend
2019-10-08  8:42   ` Toke Høiland-Jørgensen

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