From: Mauro Carvalho Chehab <mchehab@kernel.org>
To: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>,
linux-media@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 01/11] media: tm6000: fix potential Spectre variant 1
Date: Mon, 23 Apr 2018 16:17:42 -0300 [thread overview]
Message-ID: <20180423161742.66f939ba@vento.lan> (raw)
In-Reply-To: <3ab9c4c9-0656-a08e-740e-394e2e509ae9@embeddedor.com>
Em Mon, 23 Apr 2018 14:11:02 -0500
"Gustavo A. R. Silva" <gustavo@embeddedor.com> escreveu:
> On 04/23/2018 01:24 PM, Mauro Carvalho Chehab wrote:
> > Em Mon, 23 Apr 2018 12:38:03 -0500
> > "Gustavo A. R. Silva" <gustavo@embeddedor.com> escreveu:
> >
> >> f->index can be controlled by user-space, hence leading to a
> >> potential exploitation of the Spectre variant 1 vulnerability.
> >>
> >> Smatch warning:
> >> drivers/media/usb/tm6000/tm6000-video.c:879 vidioc_enum_fmt_vid_cap() warn: potential spectre issue 'format'
> >>
> >> Fix this by sanitizing f->index before using it to index
> >> array _format_
> >>
> >> Notice that given that speculation windows are large, the policy is
> >> to kill the speculation on the first load and not worry if it can be
> >> completed with a dependent load/store [1].
> >>
> >> [1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2
> >>
> >> Cc: stable@vger.kernel.org
> >> Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> >> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
> >> ---
> >> drivers/media/usb/tm6000/tm6000-video.c | 2 ++
> >> 1 file changed, 2 insertions(+)
> >>
> >> diff --git a/drivers/media/usb/tm6000/tm6000-video.c b/drivers/media/usb/tm6000/tm6000-video.c
> >> index b2399d4..d701027 100644
> >> --- a/drivers/media/usb/tm6000/tm6000-video.c
> >> +++ b/drivers/media/usb/tm6000/tm6000-video.c
> >> @@ -26,6 +26,7 @@
> >> #include <linux/kthread.h>
> >> #include <linux/highmem.h>
> >> #include <linux/freezer.h>
> >> +#include <linux/nospec.h>
> >>
> >> #include "tm6000-regs.h"
> >> #include "tm6000.h"
> >> @@ -875,6 +876,7 @@ static int vidioc_enum_fmt_vid_cap(struct file *file, void *priv,
> >> if (f->index >= ARRAY_SIZE(format))
> >> return -EINVAL;
> >>
> >> + f->index = array_index_nospec(f->index, ARRAY_SIZE(format));
> >
> > Please enlighten me: how do you think this could be exploited?
> >
> > When an application calls VIDIOC_ENUM_FMT from a /dev/video0 device,
> > it will just enumerate a hardware functionality, with is constant
> > for a given hardware piece.
> >
> > The way it works is that userspace do something like:
> >
> > int ret = 0;
> >
> > for (i = 0; ret == 0; i++) {
> > ret = ioctl(VIDIOC_ENUM_FMT, ...);
> > }
> >
> > in order to read an entire const table.
> >
> > Usually, it doesn't require any special privilege to call this ioctl,
> > but, even if someone changes its permission to 0x400, a simple lsusb
> > output is enough to know what hardware model is there. A lsmod
> > or cat /proc/modules) also tells that the tm6000 module was loaded,
> > with is a very good hint that the tm6000 is there or was there in the
> > past.
> >
> > In the specific case of tm6000, all hardware supports exactly the
> > same formats, as this is usually defined per-driver. So, a quick look
> > at the driver is enough to know exactly what the ioctl would answer.
> > Also, the net is full of other resources that would allow anyone
> > to get the supported formats for a piece of hardware.
> >
> > Even assuming that the OS doesn't have lsusb, that /proc is not
> > mounted, that /dev/video0 require special permissions, that the
> > potential attacker doesn't have physical access to the equipment (in
> > order to see if an USB board is plugged), etc... What possible harm
> > he could do by identifying a hardware feature?
> >
> > Similar notes for the other patches to drivers/media in this
> > series: let's not just start adding bloatware where not needed.
> >
> > Please notice that I'm fine if you want to submit potential
> > Spectre variant 1 fixups, but if you're willing to do so,
> > please provide an explanation about the potential threat scenarios
> > that you're identifying at the code.
> >
> > Dan,
> >
> > It probably makes sense to have somewhere at smatch a place where
> > we could explicitly mark the false-positives, in order to avoid
> > use to receive patches that would just add an extra delay where
> > it is not needed.
> >
> I see I've missed some obvious things that you've pointed out here. I'll
> mark these warnings as False Positives and take your points into account
> for the analysis of the rest of the Spectre issues reported by Smatch.
Thanks, I 'll mark this series as rejected at patchwork.linuxtv.org.
Please feel free to resubmit any patch if they represent a real
threat, adding a corresponding description about the threat scenario
at the body of the e-mail.
> Sorry for the noise and thanks for the feedback.
Anytime.
Thanks,
Mauro
next prev parent reply other threads:[~2018-04-23 19:17 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-23 17:37 [PATCH 00/11] fix potential Spectre variant 1 issues Gustavo A. R. Silva
2018-04-23 17:38 ` [PATCH 01/11] media: tm6000: fix potential Spectre variant 1 Gustavo A. R. Silva
2018-04-23 18:24 ` Mauro Carvalho Chehab
2018-04-23 19:11 ` Gustavo A. R. Silva
2018-04-23 19:17 ` Mauro Carvalho Chehab [this message]
2018-04-23 19:22 ` Gustavo A. R. Silva
2018-04-26 21:41 ` Gustavo A. R. Silva
2018-04-26 23:42 ` Mauro Carvalho Chehab
2018-05-15 3:31 ` Gustavo A. R. Silva
2018-05-15 11:59 ` Mauro Carvalho Chehab
2018-05-15 14:16 ` Dan Carpenter
2018-05-15 17:29 ` Gustavo A. R. Silva
2018-05-15 19:00 ` Mauro Carvalho Chehab
2018-05-16 13:11 ` Dan Carpenter
2018-05-16 13:36 ` Mauro Carvalho Chehab
2018-05-15 19:39 ` Dan Carpenter
2018-05-17 1:14 ` Gustavo A. R. Silva
2018-05-17 10:36 ` Gustavo A. R. Silva
2018-05-17 11:34 ` Mauro Carvalho Chehab
2018-05-17 11:43 ` Mauro Carvalho Chehab
2018-05-17 12:13 ` Mauro Carvalho Chehab
2018-05-17 18:08 ` Gustavo A. R. Silva
2018-05-21 16:18 ` Gustavo A. R. Silva
2018-04-24 9:35 ` Dan Carpenter
2018-04-24 10:11 ` Mauro Carvalho Chehab
2018-04-24 10:36 ` Peter Zijlstra
2018-04-24 11:21 ` Peter Zijlstra
2018-04-24 17:47 ` Mauro Carvalho Chehab
2018-04-24 18:48 ` Peter Zijlstra
2018-04-23 17:38 ` [PATCH 02/11] exynos4-is: mipi-csis: " Gustavo A. R. Silva
2018-04-23 17:39 ` [PATCH 03/11] fsl-viu: " Gustavo A. R. Silva
2018-04-23 17:40 ` [PATCH 04/11] marvell-ccic: mcam-core: " Gustavo A. R. Silva
2018-04-23 17:41 ` [PATCH 05/11] omap_vout: " Gustavo A. R. Silva
2018-04-23 17:47 ` [PATCH 06/11] rcar-v4l2: " Gustavo A. R. Silva
2018-04-23 17:48 ` [PATCH 07/11] rcar_drif: " Gustavo A. R. Silva
2018-04-23 17:48 ` [PATCH 08/11] sh_vou: " Gustavo A. R. Silva
2018-04-23 17:50 ` [PATCH 09/11] vimc-debayer: " Gustavo A. R. Silva
2018-04-23 17:51 ` [PATCH 10/11] vivid-sdr-cap: " Gustavo A. R. Silva
2018-04-23 17:52 ` [PATCH 11/11] vsp1_rwpf: " Gustavo A. R. Silva
2018-04-23 19:13 ` [PATCH 00/11] fix potential Spectre variant 1 issues Gustavo A. R. Silva
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