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From: "Christian König" <christian.koenig@amd.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Luben Tuikov <luben.tuikov@amd.com>
Cc: "Daniel Vetter" <daniel@ffwll.ch>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"David Airlie" <airlied@linux.ie>,
	linux-kernel-mentees@lists.linuxfoundation.org,
	"Felix Kuehling" <Felix.Kuehling@amd.com>,
	LKML <linux-kernel@vger.kernel.org>,
	"amd-gfx list" <amd-gfx@lists.freedesktop.org>,
	"Peilin Ye" <yepeilin.cs@gmail.com>,
	"Marek Olšák" <marek.olsak@amd.com>,
	"Hans de Goede" <hdegoede@redhat.com>, Trek <trek00@inbox.ru>,
	"Maling list - DRI developers" <dri-devel@lists.freedesktop.org>,
	"Thomas Zimmermann" <tzimmermann@suse.de>,
	"Alex Deucher" <alexdeucher@gmail.com>,
	"Alex Deucher" <alexander.deucher@amd.com>,
	"Evan Quan" <evan.quan@amd.com>, "Leo Liu" <leo.liu@amd.com>,
	"Nicholas Kazlauskas" <nicholas.kazlauskas@amd.com>,
	"Dan Carpenter" <dan.carpenter@oracle.com>,
	"Xiaojie Yuan" <xiaojie.yuan@amd.com>
Subject: Re: [Linux-kernel-mentees] [PATCH] drm/amdgpu: Prevent kernel-infoleak in amdgpu_info_ioctl()
Date: Fri, 31 Jul 2020 08:57:53 +0200
Message-ID: <690213fd-d3d2-2253-dcb2-367a65b34f38@amd.com> (raw)
In-Reply-To: <20200731065322.GA1518178@kroah.com>

Am 31.07.20 um 08:53 schrieb Greg Kroah-Hartman:
> On Thu, Jul 30, 2020 at 05:09:07PM -0400, Luben Tuikov wrote:
>> On 2020-07-29 9:49 a.m., Alex Deucher wrote:
>>> On Wed, Jul 29, 2020 at 4:11 AM Christian König
>>> <ckoenig.leichtzumerken@gmail.com> wrote:
>>>> Am 28.07.20 um 21:29 schrieb Peilin Ye:
>>>>> Compiler leaves a 4-byte hole near the end of `dev_info`, causing
>>>>> amdgpu_info_ioctl() to copy uninitialized kernel stack memory to userspace
>>>>> when `size` is greater than 356.
>>>>>
>>>>> In 2015 we tried to fix this issue by doing `= {};` on `dev_info`, which
>>>>> unfortunately does not initialize that 4-byte hole. Fix it by using
>>>>> memset() instead.
>>>>>
>>>>> Cc: stable@vger.kernel.org
>>>>> Fixes: c193fa91b918 ("drm/amdgpu: information leak in amdgpu_info_ioctl()")
>>>>> Fixes: d38ceaf99ed0 ("drm/amdgpu: add core driver (v4)")
>>>>> Suggested-by: Dan Carpenter <dan.carpenter@oracle.com>
>>>>> Signed-off-by: Peilin Ye <yepeilin.cs@gmail.com>
>>>> Reviewed-by: Christian König <christian.koenig@amd.com>
>>>>
>>>> I can't count how many of those we have fixed over the years.
>>>>
>>>> At some point we should probably document that using "= {}" or "= { 0 }"
>>>> in the kernel is a really bad idea and should be avoided.
>>> Moreover, it seems like different compilers seem to behave relatively
>>> differently with these and we often get reports of warnings with these
>>> on clang.  When in doubt, memset.
>> There are quite a few of those under drivers/gpu/drm, for "amd/", "scheduler/"
>> drm*.c files,
>>
>> $find . \( -regex "./drm.*\.c" -or -regex "./amd/.*\.c" -or -regex "./scheduler/.*\.c" \) -exec egrep -n -- " *= *{ *(|NULL|0) *}" \{\} \+ | wc -l
>> 374
>> $_
>>
>> Out of which only 16 are of the non-ISO C variety, "= {}",
>>
>> $find . \( -regex "./drm.*\.c" -or -regex "./amd/.*\.c" -or -regex "./scheduler/.*\.c" \) -exec egrep -n -- " *= *{ *}" \{\} \+ | wc -l
>> 16
>> $_
>>
>> Perhaps the latter are the more pressing ones, since it is a C++ initializer and not a ISO C one.
> It only matters when we care copying the data to userspace, if it all
> stays in the kernel, all is fine.

Well only as long as you don't try to compute a CRC32, MD5 or any 
fingerprint for a hash from the bytes from the structure.

Then it fails horrible and you wonder why the code doesn't works as 
expected.

Regards,
Christian.

>
> thanks,
>
> greg k-h

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Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-28 19:29 Peilin Ye
2020-07-29  8:11 ` Christian König
2020-07-29  9:00   ` Daniel Vetter
2020-07-29 13:49   ` Alex Deucher
2020-07-30 21:09     ` Luben Tuikov
2020-07-31  6:53       ` Greg Kroah-Hartman
2020-07-31  6:57         ` Christian König [this message]
2020-07-31  7:10           ` Greg Kroah-Hartman
2020-07-31  7:57             ` Christian König
2020-07-31  7:34       ` Arnd Bergmann
2020-07-29 21:55   ` Alex Deucher

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