linux-kernel - [PATCH bpf] bpf: fix argument type in bpf

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Message-ID: <20241009180500.87367-1-technoboy85@gmail.com>
Date: Wed,  9 Oct 2024 19:05:00 +0100
From: Matteo Croce <technoboy85@...il.com>
To: Andrii Nakryiko <andrii@...nel.org>,
	bpf@...r.kernel.org
Cc: Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev,
	Matteo Croce <teknoraver@...a.com>
Subject: [PATCH bpf] bpf: fix argument type in bpf_loop documentation

From: Matteo Croce <teknoraver@...a.com>

The `index` argument to bpf_loop() is threaded as an u64.
This lead in a subtle verifier denial where clang cloned the argument
in another register[1].

[1] https://github.com/systemd/systemd/pull/34650#issuecomment-2401092895

Signed-off-by: Matteo Croce <teknoraver@...a.com>
---
 include/uapi/linux/bpf.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 8ab4d8184b9d..874af0186fe8 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -5371,7 +5371,7 @@ union bpf_attr {
  *		Currently, the **flags** must be 0. Currently, nr_loops is
  *		limited to 1 << 23 (~8 million) loops.
  *
- *		long (\*callback_fn)(u32 index, void \*ctx);
+ *		long (\*callback_fn)(u64 index, void \*ctx);
  *
  *		where **index** is the current index in the loop. The index
  *		is zero-indexed.
-- 
2.46.0