Re: [PATCH 3/3] fortify: Move FORTIFY_SOURCE under 'Kernel hardening options'

[Kees Cook <kees@kernel.org>]

On Fri, Jan 17, 2025 at 01:03:37PM +0000, Mel Gorman wrote:
> FORTIFY_SOURCE is a hardening option both at build and runtime. Move
> it under 'Kernel hardening options'.
> 
> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
> ---
>  security/Kconfig           | 9 ---------
>  security/Kconfig.hardening | 9 +++++++++
>  2 files changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/security/Kconfig b/security/Kconfig
> index fe7346dc4bc3..bca84f839fbe 100644
> --- a/security/Kconfig
> +++ b/security/Kconfig
> @@ -159,15 +159,6 @@ config LSM_MMAP_MIN_ADDR
>  	  this low address space will need the permission specific to the
>  	  systems running LSM.
>  
> -config FORTIFY_SOURCE
> -	bool "Harden common str/mem functions against buffer overflows"
> -	depends on ARCH_HAS_FORTIFY_SOURCE
> -	# https://github.com/llvm/llvm-project/issues/53645
> -	depends on !CC_IS_CLANG || !X86_32
> -	help
> -	  Detect overflows of buffers in common string and memory functions
> -	  where the compiler can determine and validate the buffer sizes.
> -
>  config STATIC_USERMODEHELPER
>  	bool "Force all usermode helper calls through a single binary"
>  	help
> diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening
> index 537a6431892e..8d005fe154ef 100644
> --- a/security/Kconfig.hardening
> +++ b/security/Kconfig.hardening
> @@ -301,6 +301,15 @@ config HARDENED_USERCOPY_DEFAULT_ON
>  	  This has the effect of setting "hardened_usercopy=on" on the kernel
>  	  command line. This can be disabled with "hardened_usercopy=off".
>  
> +config FORTIFY_SOURCE
> +	bool "Harden common str/mem functions against buffer overflows"
> +	depends on ARCH_HAS_FORTIFY_SOURCE
> +	# https://github.com/llvm/llvm-project/issues/53645
> +	depends on !CC_IS_CLANG || !X86_32
> +	help
> +	  Detect overflows of buffers in common string and memory functions
> +	  where the compiler can determine and validate the buffer sizes.
> +
>  endmenu

Please move this before HARDENED_USERCOPY -- it's a more general config
and also comes first alphabetically. ;)

I would note that the LLVM bug referenced was fixed in Clang 15+, a
separate patch (not required by you) should fix that if it the tests
actually pass on x86_32 again...

>  
>  menu "Hardening of kernel data structures"
> -- 
> 2.43.0
> 

-Kees

-- 
Kees Cook