linux-kernel - Re: [PATCH bpf-next 1/2] bpf: Add a bpf_kallsyms

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Date:   Wed, 23 Dec 2020 07:50:47 +0000
From:   Christoph Hellwig <hch@...radead.org>
To:     Florent Revest <revest@...omium.org>
Cc:     Christoph Hellwig <hch@...radead.org>, Yonghong Song <yhs@...com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        KP Singh <kpsingh@...omium.org>, bpf <bpf@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Florent Revest <revest@...gle.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next 1/2] bpf: Add a bpf_kallsyms_lookup helper

On Tue, Dec 22, 2020 at 09:17:41PM +0100, Florent Revest wrote:
> On Tue, Dec 22, 2020 at 3:18 PM Christoph Hellwig <hch@...radead.org> wrote:
> >
> > FYI, there is a reason why kallsyms_lookup is not exported any more.
> > I don't think adding that back through a backdoor is a good idea.
> 
> Did you maybe mean kallsyms_lookup_name (the one that looks an address
> up based on a symbol name) ? It used to be exported but isn't anymore
> indeed.
> However, this is not what we're trying to do. As far as I can tell,
> kallsyms_lookup (the one that looks a symbol name up based on an
> address) has never been exported but its close cousins sprint_symbol
> and sprint_symbol_no_offset (which only call kallsyms_lookup and
> pretty print the result) are still exported, they are also used by
> vsprintf. Is this an issue ?

Indeed, I thought of kallsyms_lookup_name.  Let me take another
look at the patch, but kallsyms_lookup still seems like a very
lowlevel function to export to arbitrary eBPF programs.