Re: [PATCH v2] lkdtm: Add tests for LIST_POISON and ZERO_SIZE_PTR

[Greg KH]

On Fri, Dec 02, 2016 at 01:32:24PM -0800, Kees Cook wrote:
> On Thu, Dec 1, 2016 at 8:22 PM, Michael Ellerman <mpe@xxxxxxxxxxxxxx> wrote:
> > This adds two tests, to check that a read or write to LIST_POISON1 and
> > ZERO_SIZE_PTR are blocked.
> >
> > The default values for both (256 and 16) typically fall in the range
> > of valid user space addresses. However in general mmap_min_addr is 64K,
> > which prevents user space from mapping anything at those addresses.
> >
> > However it's feasible that an attacker will be able to find a way to
> > cause an access at an offset from either value, and if that offset is
> > greater than 64K then they can access user space again.
> >
> > To simulate that case, in the test we create a user mapping at
> > approximately mmap_min_addr, and offset the pointer by that amount. This
> > gives the test the greatest chance of failing (ie. an access
> > succeeding). We don't actually use mmap_min_addr, because that would
> > require exporting it to modules, instead we use the default value at
> > compile time as a reasonable approximation.
> >
> > Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> 
> Thanks for this! I like it. :)
> 
> Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
> 
> Greg, can you take this into your tree?

Sure, will do so on Monday.

thanks,

greg k-h