linux-hardening - Re: [PATCH 1/3] mm: security: Move hardened usercopy under 'Kernel hardening options'

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Message-ID: <202501201309.73DA8439B@keescook>
Date: Mon, 20 Jan 2025 13:10:44 -0800
From: Kees Cook <kees@...nel.org>
To: Mel Gorman <mgorman@...hsingularity.net>
Cc: Daniel Micay <danielmicay@...il.com>, linux-hardening@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] mm: security: Move hardened usercopy under 'Kernel
 hardening options'

On Fri, Jan 17, 2025 at 01:03:35PM +0000, Mel Gorman wrote:
> There is a submenu for 'Kernel hardening options' under "Security".
> Move HARDENED_USERCOPY under the hardening options as it is clearly
> related.
> 
> Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
> ---
>  security/Kconfig           | 12 ------------
>  security/Kconfig.hardening | 16 ++++++++++++++++
>  2 files changed, 16 insertions(+), 12 deletions(-)
> 
> diff --git a/security/Kconfig b/security/Kconfig
> index 28e685f53bd1..fe7346dc4bc3 100644
> --- a/security/Kconfig
> +++ b/security/Kconfig
> @@ -159,18 +159,6 @@ config LSM_MMAP_MIN_ADDR
>  	  this low address space will need the permission specific to the
>  	  systems running LSM.
>  
> -config HARDENED_USERCOPY
> -	bool "Harden memory copies between kernel and userspace"
> -	imply STRICT_DEVMEM
> -	help
> -	  This option checks for obviously wrong memory regions when
> -	  copying memory to/from the kernel (via copy_to_user() and
> -	  copy_from_user() functions) by rejecting memory ranges that
> -	  are larger than the specified heap object, span multiple
> -	  separately allocated pages, are not on the process stack,
> -	  or are part of the kernel text. This prevents entire classes
> -	  of heap overflow exploits and similar kernel memory exposures.
> -
>  config FORTIFY_SOURCE
>  	bool "Harden common str/mem functions against buffer overflows"
>  	depends on ARCH_HAS_FORTIFY_SOURCE
> diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening
> index c9d5ca3d8d08..00e6e2ed0c43 100644
> --- a/security/Kconfig.hardening
> +++ b/security/Kconfig.hardening
> @@ -279,6 +279,22 @@ config ZERO_CALL_USED_REGS
>  
>  endmenu
>  
> +menu "String manipulation"

I think "string" means different things to different people. I'd prefer
"Bounds checking" or "Spatial safety" if it's going to be a separate
menu section.

> +
> +config HARDENED_USERCOPY
> +	bool "Harden memory copies between kernel and userspace"
> +	imply STRICT_DEVMEM
> +	help
> +	  This option checks for obviously wrong memory regions when
> +	  copying memory to/from the kernel (via copy_to_user() and
> +	  copy_from_user() functions) by rejecting memory ranges that
> +	  are larger than the specified heap object, span multiple
> +	  separately allocated pages, are not on the process stack,
> +	  or are part of the kernel text. This prevents entire classes
> +	  of heap overflow exploits and similar kernel memory exposures.
> +
> +endmenu
> +
>  menu "Hardening of kernel data structures"

Otherwise, looks good.

-- 
Kees Cook