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

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Message-ID: <20240717205335.GA3632@sol.localdomain>
Date: Wed, 17 Jul 2024 13:53:35 -0700
From: Eric Biggers <ebiggers@...nel.org>
To: Adrian Ratiu <adrian.ratiu@...labora.com>
Cc: 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>,
	Kees Cook <kees@...nel.org>, 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 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