linux-hardening - Re: [PATCH v3 00/11] sysctl: treewide: constify ctl

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Date: Wed, 8 May 2024 13:40:38 +0200
From: Joel Granados <j.granados@...sung.com>
To: Thomas Weißschuh <linux@...ssschuh.net>
CC: Luis Chamberlain <mcgrof@...nel.org>, Kees Cook <keescook@...omium.org>,
	Eric Dumazet <edumazet@...gle.com>, Dave Chinner <david@...morbit.com>,
	<linux-fsdevel@...r.kernel.org>, <netdev@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-s390@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-riscv@...ts.infradead.org>,
	<linux-mm@...ck.org>, <linux-security-module@...r.kernel.org>,
	<bpf@...r.kernel.org>, <linuxppc-dev@...ts.ozlabs.org>,
	<linux-xfs@...r.kernel.org>, <linux-trace-kernel@...r.kernel.org>,
	<linux-perf-users@...r.kernel.org>, <netfilter-devel@...r.kernel.org>,
	<coreteam@...filter.org>, <kexec@...ts.infradead.org>,
	<linux-hardening@...r.kernel.org>, <bridge@...ts.linux.dev>,
	<lvs-devel@...r.kernel.org>, <linux-rdma@...r.kernel.org>,
	<rds-devel@....oracle.com>, <linux-sctp@...r.kernel.org>,
	<linux-nfs@...r.kernel.org>, <apparmor@...ts.ubuntu.com>
Subject: Re: [PATCH v3 00/11] sysctl: treewide: constify ctl_table argument
 of sysctl handlers

On Fri, May 03, 2024 at 04:09:40PM +0200, Thomas Weißschuh wrote:
> Hey Joel,
> 
...
> > # Motivation
> > As I read it, the motivation for these constification efforts are:
> > 1. It provides increased safety: Having things in .rodata section reduces the
> >    attack surface. This is especially relevant for structures that have function
> >    pointers (like ctl_table); having these in .rodata means that these pointers
> >    always point to the "intended" function and cannot be changed.
> > 2. Compiler optimizations: This was just a comment in the patchsets that I have
> >    mentioned ([3,4,5]). Do you know what optimizations specifically? Does it
> >    have to do with enhancing locality for the data in .rodata? Do you have other
> >    specific optimizations in mind?
> 
> I don't know about anything that would make it faster.
> It's more about safety and transmission of intent to API users,
> especially callback implementers.
Noted.

...
> > # Show the move
> > I created [8] because there is no easy way to validate which objects made it
> > into .rodata. I ran [8] for your Dec 2nd patcheset [7] and there are less in
> > .rodata than I expected (the results are in [9]) Why is that? Is it something
> > that has not been posted to the lists yet? 
> 
> Constifying the APIs only *allows* the actual table to be constified
> themselves.
> Then each table definition will have to be touched and "const" added.
That is what I thought. thx for clarifying.

> 
> See patches 17 and 18 in [7] for two examples.
> 
> Some tables in net/ are already "const" as the static definitions are
> never registered themselves but only their copies are.
> 
...

best

-- 

Joel Granados

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