Re: [PATCH v3 10/10] x86/ibt: Optimize fineibt-bhi arity 1 case

[Kees Cook]

On Wed, Feb 19, 2025 at 05:21:17PM +0100, Peter Zijlstra wrote:
> Saves a CALL to an out-of-line thunk for the common case of 1
> argument.
> 
> Suggested-by: Scott Constable <scott.d.constable@xxxxxxxxx>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> ---
>  arch/x86/include/asm/ibt.h    |    4 ++
>  arch/x86/kernel/alternative.c |   61 +++++++++++++++++++++++++++++++++++-------
>  2 files changed, 56 insertions(+), 9 deletions(-)
> 
> --- a/arch/x86/include/asm/ibt.h
> +++ b/arch/x86/include/asm/ibt.h
> @@ -70,6 +70,10 @@ static inline bool __is_endbr(u32 val)
>  	if (val == gen_endbr_poison())
>  		return true;
>  
> +	/* See cfi_fineibt_bhi_preamble() */
> +	if (IS_ENABLED(CONFIG_FINEIBT_BHI) && val == 0x001f0ff5)
> +		return true;

Does this magic value need some better documentation?

Reviewed-by: Kees Cook <kees@xxxxxxxxxx>

-- 
Kees Cook