From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Yonghong Song <yhs@fb.com>
Cc: Andrii Nakryiko <andrii@kernel.org>, bpf <bpf@vger.kernel.org>,
Networking <netdev@vger.kernel.org>,
Alexei Starovoitov <ast@fb.com>,
Daniel Borkmann <daniel@iogearbox.net>,
Kernel Team <kernel-team@fb.com>
Subject: Re: [PATCH v2 bpf-next 04/17] libbpf: mark BPF subprogs with hidden visibility as static for BPF verifier
Date: Thu, 22 Apr 2021 11:09:17 -0700 [thread overview]
Message-ID: <CAEf4BzYFHp8vt6rwgcZG5Lp-DQU0xrVq8QXvDqOyVOtx0gosnw@mail.gmail.com> (raw)
In-Reply-To: <8cde2756-e62f-7103-05b1-7d9a9d97442a@fb.com>
On Wed, Apr 21, 2021 at 10:43 PM Yonghong Song <yhs@fb.com> wrote:
>
>
>
> On 4/16/21 1:23 PM, Andrii Nakryiko wrote:
> > Define __hidden helper macro in bpf_helpers.h, which is a short-hand for
> > __attribute__((visibility("hidden"))). Add libbpf support to mark BPF
> > subprograms marked with __hidden as static in BTF information to enforce BPF
> > verifier's static function validation algorithm, which takes more information
> > (caller's context) into account during a subprogram validation.
> >
> > Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> > ---
> > tools/lib/bpf/bpf_helpers.h | 8 ++++++
> > tools/lib/bpf/btf.c | 5 ----
> > tools/lib/bpf/libbpf.c | 45 ++++++++++++++++++++++++++++++++-
> > tools/lib/bpf/libbpf_internal.h | 6 +++++
> > 4 files changed, 58 insertions(+), 6 deletions(-)
> >
> > diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
> > index 75c7581b304c..9720dc0b4605 100644
> > --- a/tools/lib/bpf/bpf_helpers.h
> > +++ b/tools/lib/bpf/bpf_helpers.h
> > @@ -47,6 +47,14 @@
> > #define __weak __attribute__((weak))
> > #endif
> >
> > +/*
> > + * Use __hidden attribute to mark a non-static BPF subprogram effectively
> > + * static for BPF verifier's verification algorithm purposes, allowing more
> > + * extensive and permissive BPF verification process, taking into account
> > + * subprogram's caller context.
> > + */
> > +#define __hidden __attribute__((visibility("hidden")))
>
> To prevent potential external __hidden macro definition conflict, how
> about
>
> #ifdef __hidden
> #undef __hidden
> #define __hidden __attribute__((visibility("hidden")))
> #endif
>
We do force #undef only with __always_inline because of the bad
definition in linux/stddef.h And we check #ifndef for __weak, because
__weak is defined in kernel headers. This is not really the case for
__hidden, the only definition is in
tools/lib/traceevent/event-parse-local.h, which I don't think we
should worry about in BPF context. So I wanted to keep it simple and
fix only if that really causes some real conflicts.
And keep in mind that in BPF code bpf_helpers.h is usually included as
one of the first few headers anyways.
> > +
> > /* When utilizing vmlinux.h with BPF CO-RE, user BPF programs can't include
> > * any system-level headers (such as stddef.h, linux/version.h, etc), and
> > * commonly-used macros like NULL and KERNEL_VERSION aren't available through
[...]
> > @@ -698,6 +700,15 @@ bpf_object__add_programs(struct bpf_object *obj, Elf_Data *sec_data,
> > if (err)
> > return err;
> >
> > + /* if function is a global/weak symbol, but has hidden
> > + * visibility (or any non-default one), mark its BTF FUNC as
> > + * static to enable more permissive BPF verification mode with
> > + * more outside context available to BPF verifier
> > + */
> > + if (GELF_ST_BIND(sym.st_info) != STB_LOCAL
> > + && GELF_ST_VISIBILITY(sym.st_other) != STV_DEFAULT)
>
> Maybe we should check GELF_ST_VISIBILITY(sym.st_other) == STV_HIDDEN
> instead?
It felt like only STV_DEFAULT should be "exported", semantically
speaking. Everything else would be treated as if it was static, except
that C rules require that function has to be global. Do you think
there is some danger to do it this way?
Currently static linker doesn't do anything special for STV_INTERNAL
and STV_PROTECTED, so we could just disable those. Do you prefer that?
I just felt that there is no risk of regression if we do this for
non-STV_DEFAULT generically.
>
> > + prog->mark_btf_static = true;
> > +
> > nr_progs++;
> > obj->nr_programs = nr_progs;
> >
[...]
next prev parent reply other threads:[~2021-04-22 18:09 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-16 20:23 [PATCH v2 bpf-next 00/17] BPF static linker: support externs Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 01/17] bpftool: support dumping BTF VAR's "extern" linkage Andrii Nakryiko
2021-04-22 3:02 ` Yonghong Song
2021-04-16 20:23 ` [PATCH v2 bpf-next 02/17] bpftool: dump more info about DATASEC members Andrii Nakryiko
2021-04-22 3:09 ` Yonghong Song
2021-04-16 20:23 ` [PATCH v2 bpf-next 03/17] libbpf: suppress compiler warning when using SEC() macro with externs Andrii Nakryiko
2021-04-22 3:47 ` Yonghong Song
2021-04-22 3:59 ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 04/17] libbpf: mark BPF subprogs with hidden visibility as static for BPF verifier Andrii Nakryiko
2021-04-22 5:43 ` Yonghong Song
2021-04-22 18:09 ` Andrii Nakryiko [this message]
2021-04-22 23:00 ` Yonghong Song
2021-04-22 23:28 ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 05/17] libbpf: allow gaps in BPF program sections to support overriden weak functions Andrii Nakryiko
2021-04-22 6:25 ` Yonghong Song
2021-04-22 18:10 ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 06/17] libbpf: refactor BTF map definition parsing Andrii Nakryiko
2021-04-22 15:33 ` Yonghong Song
2021-04-22 18:40 ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 07/17] libbpf: factor out symtab and relos sanity checks Andrii Nakryiko
2021-04-22 16:06 ` Yonghong Song
2021-04-22 18:16 ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 08/17] libbpf: make few internal helpers available outside of libbpf.c Andrii Nakryiko
2021-04-22 16:19 ` Yonghong Song
2021-04-22 18:18 ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 09/17] libbpf: extend sanity checking ELF symbols with externs validation Andrii Nakryiko
2021-04-22 16:35 ` Yonghong Song
2021-04-22 18:20 ` Andrii Nakryiko
2021-04-22 23:13 ` Yonghong Song
2021-04-16 20:23 ` [PATCH v2 bpf-next 10/17] libbpf: tighten BTF type ID rewriting with error checking Andrii Nakryiko
2021-04-22 16:50 ` Yonghong Song
2021-04-22 18:24 ` Andrii Nakryiko
2021-04-23 2:54 ` Alexei Starovoitov
2021-04-23 4:25 ` Andrii Nakryiko
2021-04-23 5:11 ` Alexei Starovoitov
2021-04-23 16:09 ` Andrii Nakryiko
2021-04-23 16:18 ` Alexei Starovoitov
2021-04-23 16:30 ` Andrii Nakryiko
2021-04-23 16:34 ` Alexei Starovoitov
2021-04-23 17:02 ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 11/17] libbpf: add linker extern resolution support for functions and global variables Andrii Nakryiko
2021-04-22 21:27 ` Yonghong Song
2021-04-22 22:12 ` Andrii Nakryiko
2021-04-22 23:57 ` Yonghong Song
2021-04-23 2:36 ` Yonghong Song
2021-04-23 4:28 ` Andrii Nakryiko
2021-04-23 4:27 ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 12/17] libbpf: support extern resolution for BTF-defined maps in .maps section Andrii Nakryiko
2021-04-22 22:56 ` Yonghong Song
2021-04-22 23:32 ` Andrii Nakryiko
2021-04-16 20:24 ` [PATCH v2 bpf-next 13/17] selftests/bpf: use -O0 instead of -Og in selftests builds Andrii Nakryiko
2021-04-23 0:05 ` Yonghong Song
2021-04-16 20:24 ` [PATCH v2 bpf-next 14/17] selftests/bpf: omit skeleton generation for multi-linked BPF object files Andrii Nakryiko
2021-04-23 0:13 ` Yonghong Song
2021-04-16 20:24 ` [PATCH v2 bpf-next 15/17] selftests/bpf: add function linking selftest Andrii Nakryiko
2021-04-23 0:50 ` Yonghong Song
2021-04-23 2:34 ` Alexei Starovoitov
2021-04-23 4:29 ` Andrii Nakryiko
2021-04-23 17:18 ` Andrii Nakryiko
2021-04-23 17:35 ` Yonghong Song
2021-04-23 17:55 ` Andrii Nakryiko
2021-04-23 17:58 ` Yonghong Song
2021-04-23 17:59 ` Andrii Nakryiko
2021-04-16 20:24 ` [PATCH v2 bpf-next 16/17] selftests/bpf: add global variables " Andrii Nakryiko
2021-04-23 1:01 ` Yonghong Song
2021-04-16 20:24 ` [PATCH v2 bpf-next 17/17] sleftests/bpf: add map " Andrii Nakryiko
2021-04-23 1:20 ` Yonghong Song
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