Bug#1113774: Disabling -fcf-protection in sudo for bookworm

[Helmut Grohne <helmut@subdivi.de>]

Hi James,

On Fri, Dec 05, 2025 at 12:38:59PM +0000, James Addison wrote:
> My reading of the thread is that fcf-protection=return can be
> security-effective on 32-bit x86 processors, has no effect on binary
> size, and does not introduce the compatibility issues that
> fcf-protection=branch does.

In order for -fcf-protection=return to provide any benefit, a shadow 
stack is required. That support has not trickled down yet. It is only 
since trixie that 64bit enables CONFIG_X86_USER_SHADOW_STACK, so no 
Debian i386 kernel ever enabled that. I also doubt that 32bit hardware 
supports this in any way.

> I think this is what Helmut was pointing out -- the two halves of the
> flag's behaviour.

My clarification was that we're disabling both features, but doing so is 
ok, because neither has any practical benefit on i386.

Helmut