From: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: Jens Wiklander <jens.wiklander@linaro.org>,
valentin.manea@huawei.com, devicetree@vger.kernel.org,
javier@javigon.com, emmanuel.michel@st.com,
Herbert Xu <herbert@gondor.apana.org.au>,
Arnd Bergmann <arnd@arndb.de>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-kernel@vger.kernel.org, jean-michel.delorme@st.com,
tpmdd-devel@lists.sourceforge.net,
linux-arm-kernel@lists.infradead.org
Subject: Re: [tpmdd-devel] [RFC PATCH 1/2] tee: generic TEE subsystem
Date: Sat, 18 Apr 2015 11:29:23 -0600 [thread overview]
Message-ID: <20150418172923.GA10605@obsidianresearch.com> (raw)
In-Reply-To: <20150418090147.GF12732@n2100.arm.linux.org.uk>
On Sat, Apr 18, 2015 at 10:01:47AM +0100, Russell King - ARM Linux wrote:
> On Fri, Apr 17, 2015 at 10:30:54AM -0600, Jason Gunthorpe wrote:
> > On Fri, Apr 17, 2015 at 09:50:56AM +0200, Jens Wiklander wrote:
> > > + teedev = devm_kzalloc(dev, sizeof(*teedev), GFP_KERNEL);
> > [..]
> > > + rc = misc_register(&teedev->miscdev);
> > [..]
> > > +void tee_unregister(struct tee_device *teedev)
> > > +{
> > [..]
> > > + misc_deregister(&teedev->miscdev);
> > > +}
> > [..]
> > >+static int optee_remove(struct platform_device *pdev)
> > >+{
> > >+ tee_unregister(optee->teedev);
> >
> > Isn't that a potential use after free? AFAIK misc_deregister does not
> > guarentee the miscdev will no longer be accessed after it returns, and
> > the devm will free it after optee_remove returns.
> >
> > Memory backing a stuct device needs to be freed via the release
> > function.
>
> Out of interest, which struct device are you talking about here?
Sorry, I was imprecise. In the first paragraph I ment 'miscdev' to
refer to the entire thing, struct tee_device, struct misc_device, the
driver allocations, etc.
So, the first issue is the use-after-free via ioctl() touching struct
tee_device that you described.
But then we trundle down to:
+ ctx->teedev->desc->ops->get_version(ctx, &vers.spec_version,
+ vers.uuid);
If we kref teedev so it is valid then calling a driver call back after
(or during) it's remove function is very likely to blow up.
Also, in TPM we discovered that adding a sysfs file was very ugly
(impossible?) because without the misc_mtx protection that open has,
getting a locked tee_device in the sysfs callback is difficult.
With TPM, we ended up trying lots of options for fixing struct
misc_device in the tpm core, which is handling multiple sub drivers,
and basically gave up. Gave each struct tpm_device an embedded struct
device like Greg suggested here. Then the tpm core is working with the
APIs, not struggling against them.
But this is not a user-space invisible change, so better to do it right
from day 1 ..
We followed rtc as an example of how to create a mid-layer that
exports it's own register function, with char dev and sysfs
components. It seems properly implemented, and has elegant solutions
to these problems (like ops):
- Don't mess with modules, use 'ops' and set 'ops' to null when the
driver removes. The driver core will keep the driver module around
for you bettwen the probe/remove calls. Setting ops = NULL ensures driver
module code cannot be called after remove.
- Use locking for 'ops' to serialize driver callbacks with driver removal
- Embed a struct device/etc in the struct tee_device and use the release
function to deallocate struct tee_device. All callbacks from the
driver/char/sysfs core can now use container_of on something that
is already holds the right kref.
- Consider an alloc/register pattern as we use now in TPM. This has proven
smart for TPM as it allows:
alloc tee_device + init struct device, etc
driver setup
core library helper calls for setup/etc
driver register + char dev publish
It appeared to me this driver was copying TPM's old architecture,
which is very much known to be broken.
Jason
next prev parent reply other threads:[~2015-04-18 17:30 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-17 7:50 [RFC PATCH 0/2] generic TEE subsystem Jens Wiklander
2015-04-17 7:50 ` [RFC PATCH 1/2] tee: " Jens Wiklander
2015-04-17 16:30 ` [tpmdd-devel] " Jason Gunthorpe
2015-04-18 9:01 ` Russell King - ARM Linux
2015-04-18 17:29 ` Jason Gunthorpe [this message]
2015-04-18 21:57 ` Russell King - ARM Linux
2015-04-20 5:08 ` Jason Gunthorpe
2015-04-20 14:54 ` Greg Kroah-Hartman
2015-04-20 15:56 ` Jason Gunthorpe
2015-04-20 16:05 ` Greg Kroah-Hartman
2015-04-20 13:02 ` Jens Wiklander
2015-04-20 17:55 ` Jason Gunthorpe
2015-04-21 5:59 ` Jens Wiklander
2015-04-17 20:07 ` Arnd Bergmann
2015-04-18 7:20 ` Paul Bolle
2015-04-20 6:20 ` Jens Wiklander
2015-04-20 18:20 ` [tpmdd-devel] " Jason Gunthorpe
2015-04-21 10:45 ` Jens Wiklander
2015-04-18 8:55 ` Greg Kroah-Hartman
2015-04-18 8:57 ` Greg Kroah-Hartman
2015-04-18 9:04 ` Russell King - ARM Linux
2015-04-18 18:47 ` Greg Kroah-Hartman
2015-04-18 19:02 ` Russell King - ARM Linux
2015-04-18 20:37 ` Greg Kroah-Hartman
2015-04-18 20:50 ` Russell King - ARM Linux
2015-04-19 7:00 ` Greg Kroah-Hartman
2015-04-17 7:50 ` [RFC PATCH 2/2] tee: add OP-TEE driver Jens Wiklander
2015-04-18 8:57 ` Greg Kroah-Hartman
2015-04-18 9:36 ` Javier González
2015-04-18 18:49 ` Greg Kroah-Hartman
2015-04-18 19:01 ` Arnd Bergmann
2015-04-19 11:17 ` Javier González
2015-04-19 19:47 ` Arnd Bergmann
2015-04-20 7:05 ` Javier González
2015-04-20 6:42 ` Jens Wiklander
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