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SubjectRe: [PATCH] arm64: CONFIG_DEVPORT should not be used when PCI is being used
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On 04/07/2016 01:26 AM, Geert Uytterhoeven wrote:
> On Thu, Apr 7, 2016 at 2:18 AM, Greg Kroah-Hartman
> <gregkh@linuxfoundation.org> wrote:
>> On Wed, Apr 06, 2016 at 03:27:20PM -0600, Al Stone wrote:
>>> On arm64 systems, using /dev/port does not really make sense; this is
>>> historically used for other architectures to access ISA IO ports, which
>>> with any luck do not exist on arm64 platforms. With the following snippet
>>> of perl code (from Jeff Bastian <jbastian@redhat.com>), we can reliably
>>> panic an arm64 system with PCI enabled:
>>>
>>> #!/usr/bin/perl -w
>>> # extracted from sensors-detect from lm_sensors
>>> # to reproduce kernel crash when probing the
>>> # Super-I/O ports
>>> use Fcntl qw(:DEFAULT :seek);
>>> sysopen(IOPORTS, "/dev/port", O_RDWR);
>>> binmode(IOPORTS);
>>> sysseek(IOPORTS, 0x2e, 0);
>>> syswrite(IOPORTS, pack("C", 0x0d), 1);
>
> There are plenty of ways to crash a system as the root user...

Of course. This was just a new one.

>>> So, make sure CONFIG_DEVPORT cannot be set on arm64; it cannot really be
>>> used and it allows us to crash a kernel from user space.
>>>
>>> Signed-off-by: Al Stone <ahs3@redhat.com>
>>> Cc: Arnd Bergmann <arnd@arndb.de>
>>> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>>> ---
>>> drivers/char/Kconfig | 2 +-
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig
>>> index b272397..c532f62 100644
>>> --- a/drivers/char/Kconfig
>>> +++ b/drivers/char/Kconfig
>>> @@ -587,7 +587,7 @@ config TELCLOCK
>>>
>>> config DEVPORT
>>> bool
>>> - depends on !M68K
>>> + depends on !M68K && !ARM64
>>
>> Why not fix the real bug here, it's odd that only these two arches need
>> this disabled, don't you agree?

Agreed. It does seem odd. I'm not sure I understand which bug you're thinking
is the real one, though -- that DEVPORT should be disabled in all places that
don't have ISA or that arm64 needs to have /dev/port work properly? Or perhaps
I missed something else entirely...

> In fact even the !M68K dependency is odd.
> The logic seems to originate from commit 153dcc54df826d2f ("[PATCH] mem driver:
> fix conditional on isa i/o support"), which accidentally changed an "||" into
> an "&&".
>
> Will send a patch later...
>
> Gr{oetje,eeting}s,
>
> Geert

Aha. I missed that bit. Sorry about that. So something like this instead:

config DEVPORT
bool
depends on ISA && PCI
default y

That makes more sense. Thanks.

--
ciao,
al
-----------------------------------
Al Stone
Software Engineer
Red Hat, Inc.
ahs3@redhat.com
-----------------------------------

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