Re: [RFC PATCH v4 2/9] x86/cet/ibt: User-mode indirect branch tracking support

[Eugene Syromiatnikov]

On Fri, Sep 21, 2018 at 08:05:46AM -0700, Yu-cheng Yu wrote:

> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index bffa9ef47832..230f65ee881e 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c

> @@ -434,6 +435,23 @@ static __init int setup_disable_shstk(char *s)
>  __setup("no_cet_shstk", setup_disable_shstk);
>  #endif
>  
> +#ifdef CONFIG_X86_INTEL_BRANCH_TRACKING_USER
> +static __init int setup_disable_ibt(char *s)
> +{
> +	/* require an exact match without trailing characters */
> +	if (strlen(s))
> +		return 0;

"s[0] (!= '\0')" will do the same check in constant time.