linux-kernel - [PATCH bpf v2 0/2] bpf, xdp: clean adjust

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Message-ID: <20250331032354.75808-1-jiayuan.chen@linux.dev>
Date: Mon, 31 Mar 2025 11:23:43 +0800
From: Jiayuan Chen <jiayuan.chen@...ux.dev>
To: bpf@...r.kernel.org
Cc: mrpre@....com,
	Jiayuan Chen <jiayuan.chen@...ux.dev>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Eduard Zingerman <eddyz87@...il.com>,
	Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>,
	Stanislav Fomichev <sdf@...ichev.me>,
	Hao Luo <haoluo@...gle.com>,
	Jiri Olsa <jolsa@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
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	Mykola Lysenko <mykolal@...com>,
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	Willem de Bruijn <willemb@...gle.com>,
	Jason Xing <kerneljasonxing@...il.com>,
	Anton Protopopov <aspsk@...valent.com>,
	Abhishek Chauhan <quic_abchauha@...cinc.com>,
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	David Lechner <dlechner@...libre.com>,
	linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org,
	linux-kselftest@...r.kernel.org
Subject: [PATCH bpf v2 0/2] bpf, xdp: clean adjust_{head,meta} memory when offset < 0

This patchset originates from my attempt to resolve a KMSAN warning that
has existed for over 3 years:
https://syzkaller.appspot.com/bug?extid=0e6ddb1ef80986bdfe64

Previously, we had a brief discussion in this thread about whether we can
simply perform memset in adjust_{head,meta}:
https://lore.kernel.org/netdev/20250328043941.085de23b@kernel.org/T/#t

Unfortunately, I couldn't find a similar topic in the mail list, but I did
find a similar security-related commit:
commit 6dfb970d3dbd ("xdp: avoid leaking info stored in frame data on page reuse")

I just create a new topic here and make subject more clear, we can discuss
this here.

Meanwhile, I also discovered a related issue that led to a CVE,specifically
the Facebook Katran vulnerability (https://vuldb.com/?id.246309).

Currently, even with unprivileged functionality disabled, a user can load
a BPF program using CAP_BPF and CAP_NET_ADMIN, which I believe we should
avoid exposing kernel memory directly to users now.

Regarding performance considerations, I added corresponding results to the
selftest, testing common MAC headers and IP headers of various sizes.

Compared to not using memset, the execution time increased by 2ns, but I
think this is negligible considering the entire net stack.

Jiayuan Chen (2):
  bpf, xdp: clean head/meta when expanding it
  selftests/bpf: add perf test for adjust_{head,meta}

 include/uapi/linux/bpf.h                      |  8 +--
 net/core/filter.c                             |  5 +-
 tools/include/uapi/linux/bpf.h                |  6 ++-
 .../selftests/bpf/prog_tests/xdp_perf.c       | 52 ++++++++++++++++---
 tools/testing/selftests/bpf/progs/xdp_dummy.c | 14 +++++
 5 files changed, 72 insertions(+), 13 deletions(-)

-- 
2.47.1