[kernel-hardening] Re: [PATCH V11 4/5] vsprintf: add printk specifier %px

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

On Wed, Nov 29, 2017 at 03:20:58PM -0800, Andrew Morton wrote:
> On Wed, 29 Nov 2017 13:05:04 +1100 "Tobin C. Harding" <me@tobin.cc> wrote:
> 
> > printk specifier %p now hashes all addresses before printing. Sometimes
> > we need to see the actual unmodified address. This can be achieved using
> > %lx but then we face the risk that if in future we want to change the
> > way the Kernel handles printing of pointers we will have to grep through
> > the already existent 50 000 %lx call sites. Let's add specifier %px as a
> > clear, opt-in, way to print a pointer and maintain some level of
> > isolation from all the other hex integer output within the Kernel.
> > 
> > Add printk specifier %px to print the actual unmodified address.
> > 
> > ...
> >
> > +Unmodified Addresses
> > +====================
> > +
> > +::
> > +
> > +	%px	01234567 or 0123456789abcdef
> > +
> > +For printing pointers when you _really_ want to print the address. Please
> > +consider whether or not you are leaking sensitive information about the
> > +Kernel layout in memory before printing pointers with %px. %px is
> > +functionally equivalent to %lx. %px is preferred to %lx because it is more
> > +uniquely grep'able. If, in the future, we need to modify the way the Kernel
> > +handles printing pointers it will be nice to be able to find the call
> > +sites.
> > +
> 
> You might want to add a checkpatch rule which emits a stern
> do-you-really-want-to-do-this warning when someone uses %px.
> 

Oh, nice idea. It has to be a CHECK but right? By stern, you mean use
stern language?

thanks,
Tobin.