[kernel-hardening] Re: [PATCH v2] printk: hash addresses printed with %p

["Tobin C. Harding" <me@tobin.cc>]

On Tue, Oct 17, 2017 at 09:31:19AM -0400, Steven Rostedt wrote:
> On Tue, 17 Oct 2017 15:52:51 +1100
> "Tobin C. Harding" <me@tobin.cc> wrote:
> 
> > Currently there are many places in the kernel where addresses are being
> > printed using an unadorned %p. Kernel pointers should be printed using
> > %pK allowing some control via the kptr_restrict sysctl. Exposing addresses
> > gives attackers sensitive information about the kernel layout in memory.
> > 
> > We can reduce the attack surface by hashing all addresses printed with
> > %p. This will of course break some users, forcing code printing needed
> > addresses to be updated.
> > 
> > For what it's worth, usage of unadorned %p can be broken down as follows
> > 
> >     git grep '%p[^KFfSsBRrbMmIiEUVKNhdDgCGO]' | wc -l
> 
> Does %p[FfSs] leak addresses? Well, I guess it does if they are not
> found in kallsyms, but otherwise you have:
> 
>   function+0x<offset>

You are correct %pF and %pS print an offset. Does this provide an attack vector,
I didn't think so but I'm no security expert. If they do then we need to amend
those calls also.

We still have %pa[pd] to see to as well obviously.

thanks for the review,
Tobin.