linux-kernel - Re: [PATCH] video: constify geode ops structures

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Message-ID: <20151109054253.GQ18797@mwanda>
Date:	Mon, 9 Nov 2015 08:42:53 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	Julia Lawall <julia.lawall@...6.fr>, Joe Perches <joe@...ches.com>
Cc:	kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org,
	Kees Cook <keescook@...omium.org>,
	kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH] video: constify geode ops structures

On Sun, Nov 08, 2015 at 10:24:49PM +0000, Julia Lawall wrote:
> On Mon, 9 Nov 2015, Dan Carpenter wrote:
> 
> > Cool.  So, in grsec they use a GCC plugin to make these const
> > automatically since they only contain function pointers.  There about
> > 100 struct types marked as __no_const.  Kees would like to adopt the
> > grsec pluggin approach I expect.  Do you have an idea how many structs
> > only contain function pointers or how many consts we would have to add
> > to get the same effect without the plugin?
> 
> My list has 373 type names.  In the list there are counts for good
> (already const) and bad (not const).  The sum of the bad values is 2467.
> The list is below.
> 
> julia

Fantastic!  Thanks.  We could autogenerate the list of type names and
make checkpatch.pl complain if we declared those types as non const.

I ran this command to find which functions grsec marks as __no_const.

egrep '(^ struct |^@@|__no_const;)' grsecurity-3.1-4.2.5-201511021814.patch | grep __no_const -B1 | grep -v __no_const | grep -v '^--' | cut -d @ -f 5-  | cut -b 9- | cut -d ' ' -f 1

There are 60 structs declared as __no_const.  For some structs they
declare a no_const version and use it as needed.  Like this:
typedef struct net_device_ops __no_const net_device_ops_no_const;

grep __no_const grsecurity-3.1-4.2.5-201511021814.patch | grep typedef | cut -d ' ' -f 3

There are 32 of those.

Then I compared to see if their structs were on your list.  For some
reason there quite a few one their list which are not on yours.  Out
of the first 10 about half weren't on your list.  cpu_cache_fns,
outer_cache_fns, psci_operations, smp_operations, omap_hwmod_soc_ops,
smp_ops_t.  These are mostly different arches?

Also bit_table has in int has well as a function pointers but it is on
their list.  I'm not sure why.  Maybe they are marking structs const
that I don't know about.

The other trick that they do is they define structs as __do_const if
they want them to be const by default, which is pretty neat.  This feels
like it should be a standard GCC feature.  In the meantime we could
mark things as __do_const and print a sparse warning if it was declared
as not const.

I have attached the list of __no_const structs.

regards,
dan carpenter

View attachment "no_const" of type "text/plain" (1404 bytes)