[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <202007161216.9C9784FEBE@keescook>
Date: Thu, 16 Jul 2020 12:22:17 -0700
From: Kees Cook <keescook@...omium.org>
To: Matthew Wilcox <willy@...radead.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Romain Perier <romain.perier@...il.com>,
Allen Pais <allen.lkml@...il.com>,
Thomas Gleixner <tglx@...utronix.de>,
Oscar Carter <oscar.carter@....com>,
Dmitry Torokhov <dmitry.torokhov@...il.com>,
Kevin Curtis <kevin.curtis@...site.co.uk>,
"David S. Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
Harald Freudenberger <freude@...ux.ibm.com>,
Heiko Carstens <hca@...ux.ibm.com>,
Vasily Gorbik <gor@...ux.ibm.com>,
Christian Borntraeger <borntraeger@...ibm.com>,
Jiri Slaby <jslaby@...e.com>, Felipe Balbi <balbi@...nel.org>,
Jason Wessel <jason.wessel@...driver.com>,
Daniel Thompson <daniel.thompson@...aro.org>,
Douglas Anderson <dianders@...omium.org>,
Mitchell Blank Jr <mitch@...oth.com>,
Julian Wiedmann <jwi@...ux.ibm.com>,
Karsten Graul <kgraul@...ux.ibm.com>,
Ursula Braun <ubraun@...ux.ibm.com>,
Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
Christian Gromm <christian.gromm@...rochip.com>,
Nishka Dasgupta <nishkadg.linux@...il.com>,
Masahiro Yamada <masahiroy@...nel.org>,
Stephen Boyd <swboyd@...omium.org>,
Wambui Karuga <wambui.karugax@...il.com>,
Guenter Roeck <linux@...ck-us.net>,
Chris Packham <chris.packham@...iedtelesis.co.nz>,
Kyungtae Kim <kt0755@...il.com>,
Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
Jonathan Corbet <corbet@....net>,
Peter Zijlstra <peterz@...radead.org>,
Will Deacon <will@...nel.org>, linux-input@...r.kernel.org,
linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
linux-s390@...r.kernel.org, devel@...verdev.osuosl.org,
linux-usb@...r.kernel.org, kgdb-bugreport@...ts.sourceforge.net,
alsa-devel@...a-project.org, kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH 3/3] tasklet: Introduce new initialization API
On Thu, Jul 16, 2020 at 04:37:04PM +0100, Matthew Wilcox wrote:
> On Wed, Jul 15, 2020 at 08:08:47PM -0700, Kees Cook wrote:
> > +#define DECLARE_TASKLET(name, _callback) \
> > +struct tasklet_struct name = { \
> > + .count = ATOMIC_INIT(0), \
> > + .callback = _callback, \
> > + .use_callback = true, \
> > +}
> > +
> > +#define DECLARE_TASKLET_DISABLED(name, _callback) \
> > +struct tasklet_struct name = { \
> > + .count = ATOMIC_INIT(1), \
> > + .callback = _callback, \
> > +}
>
> You forgot to set use_callback here.
Eek; thank you.
> > @@ -547,7 +547,10 @@ static void tasklet_action_common(struct softirq_action *a,
> > if (!test_and_clear_bit(TASKLET_STATE_SCHED,
> > &t->state))
> > BUG();
> > - t->func(t->data);
> > + if (t->use_callback)
> > + t->callback(t);
> > + else
> > + t->func(t->data);
>
> I think this is the wrong way to do the conversion. Start out by setting
> t->data to (unsigned long)t in the new initialisers. Then convert the
> drivers (all 350 of them) to the new API. Then you can get rid of 'data'
> from the tasklet_struct.
That's what I did when I converted timer_struct, and it ended up creating
a mess for Control Flow Integrity checking. (The problem isn't actually
casting .data, but rather in how the callsite calls the callback --
casting the callback assignments doesn't fix the mismatch between the
caller and the callback's expectation about the function prototype
under CFI.) I got lucky with timer_struct (in v4.14) in that not much
had been converted, and I was able to do the entire conversion in the
next kernel release.
So, this time, I'm trying to avoid the prototype mismatch mess by
providing a selector to determine which prototype the callback should
be called through, and I was happy to discover I could do it without
growing the tasklet structure. Obviously the memory corruption safety
improvement won't be realized until both .data, .use_callback, and .func
are removed, but that was true even with the earlier style of conversion.
--
Kees Cook
Powered by blists - more mailing lists
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
