From: Andrii Nakryiko <andriin@fb.com>
To: Daniel Xu <dxu@dxuuu.xyz>, Daniel Borkmann <daniel@iogearbox.net>,
"John Fastabend" <john.fastabend@gmail.com>,
"bpf@vger.kernel.org" <bpf@vger.kernel.org>,
"ast@kernel.org" <ast@kernel.org>,
Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Kernel Team <Kernel-team@fb.com>,
"peterz@infradead.org" <peterz@infradead.org>,
"mingo@redhat.com" <mingo@redhat.com>,
"acme@kernel.org" <acme@kernel.org>
Subject: Re: [PATCH v2 bpf-next 1/3] bpf: Add bpf_perf_prog_read_branches() helper
Date: Thu, 23 Jan 2020 22:41:15 +0000 [thread overview]
Message-ID: <2b11467f-9d93-8109-4561-d25ac605ef10@fb.com> (raw)
In-Reply-To: <C03IYDPABSU1.1C6OL4DJ7ID1H@dlxu-fedora-R90QNFJV>
On 1/23/20 2:30 PM, Daniel Xu wrote:
> On Thu Jan 23, 2020 at 11:23 PM, Daniel Borkmann wrote:
> [...]
>>
>> Yes, so we've been following this practice for all the BPF helpers no
>> matter
>> which program type. Though for tracing it may be up to debate whether it
>> makes
>> still sense given there's nothing to be leaked here since you can read
>> this data
>> anyway via probe read if you'd wanted to. So we might as well get rid of
>> the
>> clearing for all tracing helpers.
>
> Right, that makes sense. Do you want me to leave it in for this patchset
> and then remove all of them in a followup patchset?
>
I don't think we can remove that for existing tracing helpers (e.g.,
bpf_probe_read). There are applications that explicitly expect
destination memory to be zeroed out on failure. It's a BPF world's
memset(0).
I also wonder if BPF verifier has any extra assumptions for
ARG_PTR_TO_UNINIT_MEM w.r.t. it being initialized after helper call
(e.g., for liveness tracking).
>>
>> Different question related to your set. It looks like br_stack is only
>> available
>> on x86, is that correct? For other archs this will always bail out on
>> !br_stack
>> test. Perhaps we should document this fact so users are not surprised
>> why their
>> prog using this helper is not working on !x86. Wdyt?
>
> I think perf_event_open() should fail on !x86 if a user tries to configure
> it with branch stack collection. So there would not be the opportunity for
> the bpf prog to be attached and run. I haven't tested this, though. I'll
> look through the code / install a VM and test it.
>
> [...]
>
> Thanks,
> Daniel
>
next prev parent reply other threads:[~2020-01-23 22:41 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-22 20:22 [PATCH v2 bpf-next 0/3] Add bpf_perf_prog_read_branches() helper Daniel Xu
2020-01-22 20:22 ` [PATCH v2 bpf-next 1/3] bpf: " Daniel Xu
2020-01-23 5:39 ` John Fastabend
2020-01-23 20:09 ` Daniel Xu
2020-01-23 22:23 ` Daniel Borkmann
2020-01-23 22:30 ` Daniel Xu
2020-01-23 22:41 ` Andrii Nakryiko [this message]
2020-01-23 23:09 ` Daniel Borkmann
2020-01-23 22:44 ` Daniel Borkmann
2020-01-23 23:07 ` Martin Lau
2020-01-23 23:27 ` Daniel Xu
2020-01-22 20:22 ` [PATCH v2 bpf-next 2/3] tools/bpf: Sync uapi header bpf.h Daniel Xu
2020-01-22 20:22 ` [PATCH v2 bpf-next 3/3] selftests/bpf: add bpf_perf_prog_read_branches() selftest Daniel Xu
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=2b11467f-9d93-8109-4561-d25ac605ef10@fb.com \
--to=andriin@fb.com \
--cc=Kernel-team@fb.com \
--cc=acme@kernel.org \
--cc=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=daniel@iogearbox.net \
--cc=dxu@dxuuu.xyz \
--cc=john.fastabend@gmail.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=songliubraving@fb.com \
--cc=yhs@fb.com \
/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).