Re: [PATCH v11 16/29] x86/fpu/xstate: Support both legacy and expanded signal XSTATE size

[Thomas Gleixner]

On Fri, Oct 01 2021 at 15:37, Chang S. Bae wrote:
> @@ -1252,6 +1267,13 @@ long do_arch_prctl_state(struct task_struct *tsk, int option, unsigned long arg2
>  		if (!state_perm)
>  			return 0;
>  
> +		/*
> +		 * Disallow when sigaltstack is not enough for the
> +		 * AT_MINSIGSTKSZ value.
> +		 */
> +		if (tsk->sas_ss_size > 0 && tsk->sas_ss_size < get_sigframe_size())
> +			return -EPERM;

This is not enough:

T1
sigaltstack(minsize)
...
                            T2
                            libinit()
                            prctl(....) --> success
                            enable_amx()

libfunc()         
  if (amx_enabled())
       AMXINSN
       -->#NM --> success

handle_signal()
   die(because altstack too small);

Thanks,

        tglx