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* [PATCH bpf 0/2] bpf: Fix memory access flags in helper prototypes
@ 2026-01-07 12:21 Zesen Liu
  2026-01-07 12:21 ` [PATCH bpf 1/2] " Zesen Liu
                   ` (2 more replies)
  0 siblings, 3 replies; 7+ messages in thread
From: Zesen Liu @ 2026-01-07 12:21 UTC (permalink / raw)
  To: Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko,
	Martin KaFai Lau, Eduard Zingerman, Song Liu, Yonghong Song,
	John Fastabend, KP Singh, Stanislav Fomichev, Hao Luo, Jiri Olsa,
	Matt Bobrowski, Steven Rostedt, Masami Hiramatsu,
	Mathieu Desnoyers, David S. Miller, Eric Dumazet, Jakub Kicinski,
	Paolo Abeni, Simon Horman, Daniel Xu
  Cc: bpf, linux-kernel, linux-trace-kernel, netdev, Shuran Liu,
	Peili Gao, Haoran Ni, Zesen Liu

Hi,

This series adds missing memory access flags (MEM_RDONLY or MEM_WRITE) to
several bpf helper function prototypes that use ARG_PTR_TO_MEM but lack the
correct flag. It also adds a new check in verifier to ensure the flag is
specified.

Missing memory access flags in helper prototypes can lead to critical
correctness issues when the verifier tries to perform code optimization.
After commit 37cce22dbd51 ("bpf: verifier: Refactor helper access type
tracking"), the verifier relies on the memory access flags, rather than
treating all arguments in helper functions as potentially modifying the
pointed-to memory.

Using ARG_PTR_TO_MEM alone without flags does not make sense because:

- If the helper does not change the argument, missing MEM_RDONLY causes the
   verifier to incorrectly reject a read-only buffer.
- If the helper does change the argument, missing MEM_WRITE causes the
   verifier to incorrectly assume the memory is unchanged, leading to
   errors in code optimization.

We have already seen several reports regarding this:

- commit ac44dcc788b9 ("bpf: Fix verifier assumptions of bpf_d_path's
   output buffer") adds MEM_WRITE to bpf_d_path;
- commit 2eb7648558a7 ("bpf: Specify access type of bpf_sysctl_get_name
   args") adds MEM_WRITE to bpf_sysctl_get_name.

This series looks through all prototypes in the kernel and completes the
flags. It also adds a new check (check_func_proto) in
verifier.c to statically restrict ARG_PTR_TO_MEM from appearing without
memory access flags. 

Thanks,

Zesen Liu

---
Zesen Liu (2):
      bpf: Fix memory access flags in helper prototypes
      bpf: Require ARG_PTR_TO_MEM with memory flag

 kernel/bpf/helpers.c     |  2 +-
 kernel/bpf/syscall.c     |  2 +-
 kernel/bpf/verifier.c    | 17 +++++++++++++++++
 kernel/trace/bpf_trace.c |  6 +++---
 net/core/filter.c        |  8 ++++----
 5 files changed, 26 insertions(+), 9 deletions(-)
---
base-commit: ab86d0bf01f6d0e37fd67761bb62918321b64efc
change-id: 20251220-helper_proto-fb6e64182467

Best regards,
-- 
Zesen Liu <ftyghome@gmail.com>


^ permalink raw reply	[flat|nested] 7+ messages in thread
[parent not found: <20260107-helper_proto-v1-0-21fa523fccfd@gmail.com>]

end of thread, other threads:[~2026-01-07 21:01 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2026-01-07 12:21 [PATCH bpf 0/2] bpf: Fix memory access flags in helper prototypes Zesen Liu
2026-01-07 12:21 ` [PATCH bpf 1/2] " Zesen Liu
2026-01-07 12:21 ` [PATCH bpf 2/2] bpf: Require ARG_PTR_TO_MEM with memory flag Zesen Liu
2026-01-07 12:44   ` bot+bpf-ci
2026-01-07 13:03     ` Zesen Liu
2026-01-07 21:01 ` [syzbot ci] Re: bpf: Fix memory access flags in helper prototypes syzbot ci
     [not found] <20260107-helper_proto-v1-0-21fa523fccfd@gmail.com>
2026-01-07 12:16 ` [PATCH bpf 1/2] " Zesen Liu

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