From: Steven Rostedt <rostedt@goodmis.org>
To: Matt Mullins <mmullins@mmlx.us>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
paulmck <paulmck@kernel.org>, Ingo Molnar <mingo@redhat.com>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Dmitry Vyukov <dvyukov@google.com>,
Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
Yonghong Song <yhs@fb.com>, Andrii Nakryiko <andriin@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@chromium.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
netdev <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>
Subject: Re: [PATCH] bpf: don't fail kmalloc while releasing raw_tp
Date: Tue, 17 Nov 2020 20:09:22 -0500 [thread overview]
Message-ID: <20201117200922.195ba28c@oasis.local.home> (raw)
In-Reply-To: <20201118004242.rygrwivqcdgeowi7@hydra.tuxags.com>
On Tue, 17 Nov 2020 16:42:44 -0800
Matt Mullins <mmullins@mmlx.us> wrote:
> > Indeed with a stub function, I don't see any need for READ_ONCE/WRITE_ONCE.
>
> I'm not sure if this is a practical issue, but without WRITE_ONCE, can't
> the write be torn? A racing __traceiter_ could potentially see a
> half-modified function pointer, which wouldn't work out too well.
This has been discussed before, and Linus said:
"We add READ_ONCE and WRITE_ONCE annotations when they make sense. Not
because of some theoretical "compiler is free to do garbage"
arguments. If such garbage happens, we need to fix the compiler"
https://lore.kernel.org/lkml/CAHk-=wi_KeD1M-_-_SU_H92vJ-yNkDnAGhAS=RR1yNNGWKW+aA@mail.gmail.com/
>
> This was actually my gut instinct before I wrote the __GFP_NOFAIL
> instead -- currently that whole array's memory ordering is provided by
> RCU and I didn't dive deep enough to evaluate getting too clever with
> atomic modifications to it.
The pointers are always going to be the architecture word size (by
definition), and any compiler that tears a write of a long is broken.
-- Steve
next prev parent reply other threads:[~2020-11-18 1:09 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-02 11:54 KASAN: vmalloc-out-of-bounds Read in bpf_trace_run3 syzbot
2020-11-11 14:57 ` Dmitry Vyukov
2020-11-13 5:37 ` Matt Mullins
2020-11-13 16:08 ` Yonghong Song
2021-02-10 18:23 ` Eric Dumazet
2021-02-10 19:52 ` Steven Rostedt
2020-11-15 5:52 ` [PATCH] bpf: don't fail kmalloc while releasing raw_tp Matt Mullins
2020-11-16 17:19 ` Steven Rostedt
2020-11-16 20:37 ` Mathieu Desnoyers
2020-11-16 20:44 ` Steven Rostedt
2020-11-16 21:02 ` Steven Rostedt
2020-11-16 21:06 ` Steven Rostedt
2020-11-16 21:34 ` Mathieu Desnoyers
2020-11-16 22:10 ` Steven Rostedt
2020-11-17 23:05 ` Mathieu Desnoyers
2020-11-18 0:42 ` Matt Mullins
2020-11-18 1:09 ` Steven Rostedt [this message]
2020-11-18 4:57 ` Paul E. McKenney
2020-11-16 21:21 ` Mathieu Desnoyers
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