Re: [PATCH] lkdtm: fix ACCESS_USERSPACE test

[Stephen Smalley <sds@tycho.nsa.gov>]

On 10/27/2015 08:12 PM, Greg KH wrote:
> On Tue, Oct 27, 2015 at 04:47:53PM -0400, Stephen Smalley wrote:
>> Add a copy_to_user() call to the ACCESS_USERSPACE test
>> prior to attempting direct dereferencing of the user
>> address to ensure the page is present.  Otherwise,
>> a fault occurs on arm kernels even prior to the introduction
>> of CONFIG_CPU_SW_DOMAIN_PAN, and there is no difference in
>> behavior for CONFIG_CPU_SW_DOMAIN_PAN=n vs CONFIG_CPU_SW_DOMAIN_PAN=y.
>>
>> Before this change, for any value of CONFIG_CPU_SW_DOMAIN_PAN:
>> lkdtm: Performing direct entry ACCESS_USERSPACE
>> lkdtm: attempting bad read at b6fe8000
>> Unable to handle kernel paging request at virtual address b6fe8000
>>
>> After this change, for CONFIG_CPU_SW_DOMAIN_PAN=n:
>> lkdtm: Performing direct entry ACCESS_USERSPACE
>> lkdtm: attempting bad read at b6efc000
>> lkdtm: attempting bad write at b6efc000
>>
>> After this change, for CONFIG_CPU_SW_DOMAIN_PAN=y:
>> lkdtm: Performing direct entry ACCESS_USERSPACE
>> lkdtm: attempting bad read at b6f7d000
>> Unhandled fault: page domain fault (0x01b) at 0xb6f7d000
>> ...
>>
>> Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
>> ---
>>  drivers/misc/lkdtm.c | 8 +++++++-
>>  1 file changed, 7 insertions(+), 1 deletion(-)
>
> Should this also be applied to older kernels (i.e. a stable fix)?

I don't think it qualifies (only a fix for a kernel crash test), but will defer to Kees.