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

[Eric Biggers]

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?

- Eric