Re: [PATCH 2/4] mm: security: Allow default HARDENED_USERCOPY to be set at compile time

[David Laight]

...  
> > +config HARDENED_USERCOPY_DEFAULT_ON
> > +	bool "Harden memory copies by default"
> > +	depends on HARDENED_USERCOPY
> > +	default n  
> 
> This must be "default HARDENED_USERCOPY" or existing distro builds will
> break. All major distros enable this by default, and I don't want to
> risk HARDENED_USERCOPY_DEFAULT_ON getting missed and getting globally
> disabled.

It'll also cause grief for anyone trying to bisect.
Although that is always going to go wrong if it has been disabled.

I had 'fun' trying to locate a massive slowdown of a single threaded
program that was caused by a side effect of one of the speculative
execution mitigations getting enabled because the config parameter
got renamed.

	David