linux-kernel - Re: [RFC PATCH stable 5.4 0/8] bpf: Fix bpf_probe_read/bpf_probe_read

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Message-ID: <ZHOzaStC0WmTvwL9@krava>
Date:   Sun, 28 May 2023 22:02:49 +0200
From:   Jiri Olsa <olsajiri@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     stable@...r.kernel.org, linux-mm@...ck.org, bpf@...r.kernel.org,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Tsahee Zidenberg <tsahee@...apurnalabs.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Christoph Hellwig <hch@....de>,
        Daniel Borkmann <daniel@...earbox.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Mahé Tardy <mahe.tardy@...valent.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH stable 5.4 0/8] bpf: Fix
 bpf_probe_read/bpf_probe_read_str helpers

On Fri, May 26, 2023 at 07:54:17PM +0100, Greg KH wrote:
> On Mon, May 22, 2023 at 10:33:44PM +0200, Jiri Olsa wrote:
> > hi,
> > we see broken access to user space with bpf_probe_read/bpf_probe_read_str
> > helpers on arm64 with 5.4 kernel. The problem is that both helpers try to
> > read user memory by calling probe_kernel_read, which seems to work on x86
> > but fails on arm64.
> 
> Has this ever worked on arm64 for the 5.4 kernel tree?  If not, it's not
> really a regression, and so, why not use a newer kernel that has this
> new feature added to it there?
> 
> In other words, what requires you to use the 5.4.y tree and requires
> feature parity across architectures?

we have a customer running ok on x86 v5.4, but arm64 is broken with
the same bpf/user space code

upgrade is an option of course, but it's not a big change and we can
have 5.4 working on arm64 as well

I can send out the change that will be closer to upstream changes,
if that's a concern.. with adding the new probe helpers, which I
guess is not a problem, because it does not change current API

jirka