linux-hardening - Re: [PATCH] proc: add config to block FOLL

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Message-ID: <202407171426.4DE97F7@keescook>
Date: Wed, 17 Jul 2024 14:28:29 -0700
From: Kees Cook <kees@...nel.org>
To: Eric Biggers <ebiggers@...nel.org>
Cc: Adrian Ratiu <adrian.ratiu@...labora.com>,
	linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org, kernel@...labora.com,
	gbiv@...gle.com, inglorion@...gle.com, ajordanr@...gle.com,
	Doug Anderson <dianders@...omium.org>, Jeff Xu <jeffxu@...gle.com>,
	Jann Horn <jannh@...gle.com>,
	Christian Brauner <brauner@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] proc: add config to block FOLL_FORCE in mem writes

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