Re: [PATCH bpf-next 1/2] bpf: Add a bpf_kallsyms_lookup helper

From: Florent Revest <revest@chromium.org>
To: KP Singh <kpsingh@chromium.org>
Cc: bpf <bpf@vger.kernel.org>, Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	Florent Revest <revest@google.com>,
	open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH bpf-next 1/2] bpf: Add a bpf_kallsyms_lookup helper
Date: Fri, 27 Nov 2020 10:25:08 +0100	[thread overview]
Message-ID: <c5af620d027aba9c3cdf2d642c3611f908638a3c.camel@chromium.org> (raw)
In-Reply-To: <CACYkzJ65P5fxW1bxVXm_ehLLE=gn6nuR+UVxYWjqSJfXoZd+8g@mail.gmail.com>

On Fri, 2020-11-27 at 03:32 +0100, KP Singh wrote:
> > +       ret = strlen(name) + 1;
> > +       if (symbol_size) {
> > +               strncpy(symbol, name, symbol_size);
> > +               symbol[symbol_size - 1] = '\0';
> > +       }
> > +
> > +       if (modname && module_size) {
> > +               strncpy(module, modname, module_size);
> 
> The return value does not seem to be impacted by the truncation of
> the module name, I wonder if it is better to just use a single
> buffer.
> 
> For example, the proc kallsyms shows symbols as:
> 
> <symbol_name> [module_name]
> 
> https://github.com/torvalds/linux/blob/master/kernel/kallsyms.c#L648
> 
> The square brackets do seem to be a waste here, so maybe we could use
> a single character as a separator?

I prefer Yongonhong's suggestion of having two helpers. This gives more
control to the BPF program. For example, they could decide to audit
only addresses coming from a module, and that would be easier to do
with two helpers than by parsing a string in BPF.