From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: Jakub Kicinski <jakub.kicinski@netronome.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>,
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 v2 1/5] bpf: Support injecting chain calls into BPF programs on load
Date: Sun, 06 Oct 2019 17:52:09 +0200 [thread overview]
Message-ID: <87v9t1na6u.fsf@toke.dk> (raw)
In-Reply-To: <20191005203945.6b3845a9@cakuba.netronome.com>
Jakub Kicinski <jakub.kicinski@netronome.com> writes:
> On Sat, 05 Oct 2019 12:29:14 +0200, Toke Høiland-Jørgensen wrote:
>> >> +static int bpf_inject_chain_calls(struct bpf_verifier_env *env)
>> >> +{
>> >> + struct bpf_prog *prog = env->prog;
>> >> + struct bpf_insn *insn = prog->insnsi;
>> >> + int i, cnt, delta = 0, ret = -ENOMEM;
>> >> + const int insn_cnt = prog->len;
>> >> + struct bpf_array *prog_array;
>> >> + struct bpf_prog *new_prog;
>> >> + size_t array_size;
>> >> +
>> >> + struct bpf_insn call_next[] = {
>> >> + BPF_LD_IMM64(BPF_REG_2, 0),
>> >> + /* Save real return value for later */
>> >> + BPF_MOV64_REG(BPF_REG_6, BPF_REG_0),
>> >> + /* First try tail call with index ret+1 */
>> >> + BPF_MOV64_REG(BPF_REG_3, BPF_REG_0),
>> >
>> > Don't we need to check against the max here, and spectre-proofing
>> > here?
>>
>> No, I don't think so. This is just setting up the arguments for the
>> BPF_TAIL_CALL instruction below. The JIT will do its thing with that and
>> emit the range check and the retpoline stuff...
>
> Sorry, wrong CPU bug, I meant Meltdown :)
>
> https://elixir.bootlin.com/linux/v5.4-rc1/source/kernel/bpf/verifier.c#L9029
Ah, right. Well, it only adds those extra instructions if
bpf_map_ptr_unpriv() returns true. So I figured that since we're
injecting a pointer here that is not from a userspace map, it was not
needed. Though I must admit I didn't look too closely at exactly which
conditions would make bpf_map_ptr_unpriv() return true... :)
-Toke
next prev parent reply other threads:[~2019-10-06 15:52 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-04 17:22 [PATCH bpf-next v2 0/5] xdp: Support multiple programs on a single interface through chain calls Toke Høiland-Jørgensen
2019-10-04 17:22 ` [PATCH bpf-next v2 1/5] bpf: Support injecting chain calls into BPF programs on load Toke Høiland-Jørgensen
2019-10-04 20:51 ` kbuild test robot
2019-10-04 21:12 ` kbuild test robot
2019-10-04 23:17 ` Jakub Kicinski
2019-10-05 10:29 ` Toke Høiland-Jørgensen
2019-10-06 3:39 ` Jakub Kicinski
2019-10-06 15:52 ` Toke Høiland-Jørgensen [this message]
2019-10-05 10:32 ` Toke Høiland-Jørgensen
2019-10-07 0:27 ` Alexei Starovoitov
2019-10-07 10:11 ` Toke Høiland-Jørgensen
2019-10-07 20:22 ` Daniel Borkmann
2019-10-08 9:00 ` Toke Høiland-Jørgensen
2019-10-07 20:45 ` Alexei Starovoitov
2019-10-08 9:02 ` Toke Høiland-Jørgensen
2019-10-04 17:22 ` [PATCH bpf-next v2 2/5] bpf: Add support for setting chain call sequence for programs Toke Høiland-Jørgensen
2019-10-04 23:18 ` Jakub Kicinski
2019-10-05 10:30 ` Toke Høiland-Jørgensen
2019-10-04 17:22 ` [PATCH bpf-next v2 3/5] tools: Update bpf.h header for program chain calls Toke Høiland-Jørgensen
2019-10-04 17:22 ` [PATCH bpf-next v2 4/5] libbpf: Add syscall wrappers for BPF_PROG_CHAIN_* commands Toke Høiland-Jørgensen
2019-10-04 17:22 ` [PATCH bpf-next v2 5/5] selftests: Add tests for XDP chain calls Toke Høiland-Jørgensen
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