From: Rusty Russell <rusty@rustcorp.com.au>
To: Jesper Juhl <jesper.juhl@gmail.com>
Cc: Ashutosh Naik <ashutosh.naik@gmail.com>,
anandhkrishnan@yahoo.co.in, linux-kernel@vger.kernel.org,
rth@redhat.com, akpm@osdl.org, Greg KH <greg@kroah.com>,
alan@lxorguk.ukuu.org.uk
Subject: Re: [RFC][PATCH] Prevent overriding of Symbols in the Kernel, avoiding Undefined behaviour
Date: Wed, 14 Dec 2005 13:03:35 +1100 [thread overview]
Message-ID: <1134525816.30383.13.camel@localhost.localdomain> (raw)
In-Reply-To: <9a8748490512130849o73c14313l166e6dd360f32d70@mail.gmail.com>
On Tue, 2005-12-13 at 17:49 +0100, Jesper Juhl wrote:
> On 12/13/05, Ashutosh Naik <ashutosh.naik@gmail.com> wrote:
> > On 12/13/05, Rusty Russell <rusty@rustcorp.com.au> wrote:
> > >
> > > How about something like:
> > >
> [snip imrovement suggestion]
> >
> > Have tried that in the attached patch. However, mod->syms[i].name
> > would be valid only after a long relocation for loop has run through.
> > While this adds a wee bit extra overhead, that overhead is only in the
> > case where the module does actually export a Duplicate Symbol.
> >
> > This its a question, whether we do the search before relocation ( A
> > little messier ) or after ( More straight forward)
Hi Ashutosh, Jasper,
Patch looks good! A few nits still:
> > +static int verify_export_symbols(struct module *mod)
> > +{
> > + const char *name=0;
>
> CodingStyle issue :
> const char *name = 0;
More importantly:
const char *name = NULL; /* GCC 4.0 warns */
(I assume that's why you have the useless initialization).
> > + spin_lock_irq(&modlist_lock);
> > + for (i = 0; i < mod->num_syms; i++)
> > + if (unlikely(__find_symbol(mod->syms[i].name, &owner, &crc,1))) {
>
> CodingStyle issue :
> if (unlikely(__find_symbol(mod->syms[i].name, &owner, &crc, 1))) {
I would discard the unlikely() here; it's a completely wasted
micro-optimization in this context
> > + if (ret)
> > + printk("%s: exports duplicate symbol %s (owned by %s)\n",
>
> I still think this should be printk(KERN_ERROR ...) and not just a
> warning, since the loading of the module will fail completely. Others
> may disagree ofcourse, but that's my oppinion.
I agree, KERN_ERR is appropriate here.
> I still worry a bit about the spinlock hold time, especially since you
> are doing two linear searches through what could potentially be a
> *lot* of symbols.. It may not be a problem (do you have any time
> measurements?), but it still seems to me that using a lock type that
> allows you to sleep + a call to schedule() would be a good thing for
> those loops.
We already do this to resolve (more) symbols, so I don't see it as a
problem. However, I believe that lock is redundant here: we need both
locks to write the list, but either is sufficient for reading, and we
already hold the sem.
Cheers,
Rusty.
--
ccontrol: http://ozlabs.org/~rusty/ccontrol
next prev parent reply other threads:[~2005-12-14 2:03 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-12-12 12:39 [RFC][PATCH] Prevent overriding of Symbols in the Kernel, avoiding Undefined behaviour Ashutosh Naik
2005-12-12 12:44 ` Ashutosh Naik
2005-12-12 22:25 ` Jesper Juhl
2005-12-13 8:23 ` Anand H. Krishnan
2005-12-12 19:13 ` Andrew Morton
2005-12-12 19:27 ` Richard Henderson
2005-12-12 20:20 ` Greg KH
2005-12-12 20:30 ` Jesper Juhl
2005-12-12 22:48 ` Alan Cox
2005-12-13 8:03 ` Arjan van de Ven
2005-12-13 14:32 ` Ashutosh Naik
2005-12-12 22:01 ` Rusty Russell
2005-12-13 14:26 ` Ashutosh Naik
2005-12-13 15:28 ` Ashutosh Naik
2005-12-13 16:49 ` [RFC][PATCH] " Jesper Juhl
2005-12-14 2:03 ` Rusty Russell [this message]
2005-12-14 4:10 ` Ashutosh Naik
2005-12-14 5:02 ` Ashutosh Naik
2005-12-15 4:40 ` Andrew Morton
2005-12-15 5:15 ` Rusty Russell
2005-12-15 5:45 ` Ashutosh Naik
2005-12-14 5:46 ` Ashutosh Naik
2005-12-14 23:02 ` Rusty Russell
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