Re: [PATCH 3/4] x86/traps: use entry_ssp in fixup_exception_return()

[Andrew Cooper]

On 28/02/2024 1:52 pm, Jan Beulich wrote:
> --- a/xen/arch/x86/traps.c
> +++ b/xen/arch/x86/traps.c
> @@ -837,24 +825,26 @@ static void fixup_exception_return(struc
>  {
>      if ( IS_ENABLED(CONFIG_XEN_SHSTK) )
>      {
> -        unsigned long ssp, *ptr, *base;
> +        unsigned long ssp = rdssp();
>  
> -        if ( (ssp = rdssp()) == SSP_NO_SHSTK )
> -            goto shstk_done;
> +        if ( ssp != SSP_NO_SHSTK )
> +        {
> +            unsigned long *ptr = _p(regs->entry_ssp);

To double check, this works by the magic of:

    signed long entry_ssp:48;

getting sign extended back into a canonical address?

~Andrew