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

Kees Cook
2024-07-17T21:28:29Z

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