From: Jiri Olsa <jolsa@redhat.com>
To: Yonghong Song <yhs@fb.com>
Cc: Jiri Olsa <jolsa@kernel.org>, Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"bpf@vger.kernel.org" <bpf@vger.kernel.org>,
Andrii Nakryiko <andriin@fb.com>, Martin Lau <kafai@fb.com>,
Jakub Kicinski <jakub.kicinski@netronome.com>,
David Miller <davem@redhat.com>
Subject: Re: Re: [PATCH 1/5] bpf: Allow non struct type for btf ctx access
Date: Wed, 8 Jan 2020 15:38:59 +0100 [thread overview]
Message-ID: <20200108143859.GF387467@krava> (raw)
In-Reply-To: <962209d7-cdfa-9ee3-8a12-6375091843cf@fb.com>
On Tue, Jan 07, 2020 at 06:28:11PM +0000, Yonghong Song wrote:
SNIP
> >> index ed2075884724..650df4ed346e 100644
> >> --- a/kernel/bpf/btf.c
> >> +++ b/kernel/bpf/btf.c
> >> @@ -3633,7 +3633,7 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
> >> const struct bpf_prog *prog,
> >> struct bpf_insn_access_aux *info)
> >> {
> >> - const struct btf_type *t = prog->aux->attach_func_proto;
> >> + const struct btf_type *tp, *t = prog->aux->attach_func_proto;
> >> struct bpf_prog *tgt_prog = prog->aux->linked_prog;
> >> struct btf *btf = bpf_prog_get_target_btf(prog);
> >> const char *tname = prog->aux->attach_func_name;
> >> @@ -3695,6 +3695,17 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
> >> */
> >> return true;
> >>
> >> + tp = btf_type_by_id(btf, t->type);
> >> + /* skip modifiers */
> >> + while (btf_type_is_modifier(tp))
> >> + tp = btf_type_by_id(btf, tp->type);
> >> +
> >> + if (btf_type_is_int(tp))
> >> + /* This is a pointer scalar.
> >> + * It is the same as scalar from the verifier safety pov.
> >> + */
> >> + return true;
> >
> > This should work since:
> > - the int pointer will be treated as a scalar later on
> > - bpf_probe_read() will be used to read the contents
> >
> > I am wondering whether we should add proper verifier support
> > to allow pointer to int ctx access. There, users do not need
> > to use bpf_probe_read() to dereference the pointer.
> >
> > Discussed with Martin, maybe somewhere in check_ptr_to_btf_access(),
> > before btf_struct_access(), checking if it is a pointer to int/enum,
> > it should just allow and return SCALAR_VALUE.
>
> double checked check_ptr_to_btf_access() and btf_struct_access().
> btf_struct_access() already returns SCALAR_VALUE for pointer to
> int/enum. So verifier change is probably not needed.
ok, great
>
> In your above code, could you do
> btf_type_is_int(t) || btf_type_is_enum(t)
> which will cover pointer to enum as well?
sure, I'll include that
thanks,
jirka
next prev parent reply other threads:[~2020-01-08 14:39 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-29 14:37 [RFC 0/5] bpf: Add trampoline helpers Jiri Olsa
2019-12-29 14:37 ` [PATCH 1/5] bpf: Allow non struct type for btf ctx access Jiri Olsa
2020-01-06 21:36 ` Yonghong Song
2020-01-07 12:13 ` Jiri Olsa
2020-01-07 15:50 ` Jiri Olsa
2020-01-07 17:55 ` Yonghong Song
2020-01-07 18:28 ` Yonghong Song
2020-01-08 14:38 ` Jiri Olsa [this message]
2019-12-29 14:37 ` [PATCH 2/5] bpf: Add bpf_perf_event_output_kfunc Jiri Olsa
2020-01-06 23:27 ` Alexei Starovoitov
2020-01-07 12:25 ` Jiri Olsa
2020-01-07 22:13 ` Alexei Starovoitov
2020-01-08 10:24 ` Jiri Olsa
2019-12-29 14:37 ` [PATCH 3/5] bpf: Add bpf_get_stackid_kfunc Jiri Olsa
2019-12-29 14:37 ` [PATCH 4/5] bpf: Add bpf_get_stack_kfunc Jiri Olsa
2019-12-29 14:37 ` [PATCH 5/5] bpf: Allow to resolve bpf trampoline in unwind Jiri Olsa
2020-01-06 23:46 ` Alexei Starovoitov
2020-01-07 8:30 ` Daniel Borkmann
2020-01-07 13:15 ` Jiri Olsa
2020-01-07 19:30 ` Daniel Borkmann
2020-01-07 13:05 ` Jiri Olsa
2020-01-07 13:30 ` Björn Töpel
2020-01-13 9:43 ` Jiri Olsa
2020-01-13 12:21 ` Björn Töpel
2020-01-13 12:31 ` Björn Töpel
2020-01-13 12:37 ` Jiri Olsa
2020-02-03 19:58 ` Jiri Olsa
2020-02-03 20:27 ` Björn Töpel
2020-02-03 20:45 ` Toke Høiland-Jørgensen
2020-02-04 8:18 ` Jiri Olsa
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