[PATCH] proc: add config to block FOLL_FORCE in mem writes

[Kees Cook]

On Wed, Jul 17, 2024 at 01:53:35PM -0700, Eric Biggers wrote:
> On Wed, Jul 17, 2024 at 02:13:58PM +0300, Adrian Ratiu wrote:
> > +config SECURITY_PROC_MEM_RESTRICT_FOLL_FORCE
> > +	bool "Remove FOLL_FORCE usage from /proc/pid/mem writes"
> > +	default n
> > +	help
> > +	  This restricts FOLL_FORCE flag usage in procfs mem write calls
> > +	  because it bypasses memory permission checks and can be used by
> > +	  attackers to manipulate process memory contents that would be
> > +	  otherwise protected.
> > +
> > +	  Enabling this will break GDB, gdbserver and other debuggers
> > +	  which require FOLL_FORCE for basic functionalities.
> > +
> > +	  If you are unsure how to answer this question, answer N.
> 
> FOLL_FORCE is an internal flag, and people who aren't kernel developers aren't
> going to know what it is.  Could this option be named and documented in a way
> that would be more understandable to people who aren't kernel developers?  What
> is the effect on how /proc/pid/mem behaves?

"Do not bypass RO memory permissions via /proc/$pid/mem writes" ?

-- 
Kees Cook