Re: [PATCH] lkdtm: fix ACCESS_USERSPACE test

[Stephen Smalley]

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@xxxxxxxxxxxxx>
> > ---
> >  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.

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