Re: [PATCH] RISC-V/bpf: Enable bpf_probe_read{, str}()

From: Yixun Lan <dlan@gentoo.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: Yonghong Song <yhs@fb.com>,
	Andrii Nakryiko <andrii.nakryiko@gmail.com>,
	Alan Maguire <alan.maguire@oracle.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	linux-riscv@lists.infradead.org,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@kernel.org>,
	open list <linux-kernel@vger.kernel.org>,
	Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>
Subject: Re: [PATCH] RISC-V/bpf: Enable bpf_probe_read{, str}()
Date: Sat, 9 Jul 2022 09:01:10 +0800	[thread overview]
Message-ID: <YsjTVvyqdVGy1uYZ@ofant> (raw)
In-Reply-To: <YsUzX2IeNb/u9VmN@infradead.org>

Hi Christoph, YongHong

On 00:01 Wed 06 Jul     , Christoph Hellwig wrote:
> On Tue, Jul 05, 2022 at 11:41:30PM -0700, Yonghong Song wrote:
> > 
> > 
> > On 7/5/22 10:00 PM, Andrii Nakryiko wrote:
> > > On Sun, Jul 3, 2022 at 10:53 PM Christoph Hellwig <hch@infradead.org> wrote:
> > > > 
> > > > On Sun, Jul 03, 2022 at 09:09:24PM +0800, Yixun Lan wrote:
> > > > > Enable this option to fix a bcc error in RISC-V platform
> > > > > 
> > > > > And, the error shows as follows:
> > > > 
> > > > These should not be enabled on new platforms.  Use the proper helpers
> > > > to probe kernel vs user pointers instead.
> > > 
> > > riscv existed as of [0], so I'd argue it is a proper bug fix, as
> > > corresponding select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE should
> > > have been added back then.
> > > 
> > > But I also agree that BCC tools should be updated to use proper
> > > bpf_probe_read_{kernel,user}[_str()] helpers, please contribute such
> > > fixes to BCC tools and BCC itself as well. Cc'ed Alan as his ksnoop in
> > > libbpf-tools seems to be using bpf_probe_read() as well and needs to
> > > be fixed.
> > 
> > Yixun, the bcc change looks like below:
> 
> No, this is broken.  bcc needs to stop using bpf_probe_read entirely
> for user addresses and unconditionally use bpf_probe_read_user first
> and only fall back to bpf_probe_read if not supported.
I agree with Christoph, there is something in the bcc tools that
need to adjust in order to use new bpf_probe_read_{kernel,user}

Please check the ongoing discussion [0] in the bcc tools if you're
interested in, advice and comments are welcome

[0] https://github.com/iovisor/bcc/pull/4085#issuecomment-1179446738

-- 
Yixun Lan (dlan)
Gentoo Linux Developer
GPG Key ID AABEFD55