Re: [patch V3 66/66] x86/fpu/signal: Let xrstor handle the features to init

[Borislav Petkov]

On Fri, Jun 18, 2021 at 04:19:29PM +0200, Thomas Gleixner wrote:
> There is no reason to do an extra XRSTOR from initfp_state for feature bits
> which have been cleared by user space in the FX magic xfeatures storage.
> 
> Just clear them in the task's XSTATE header and do a full restore which
> will put these cleared features into init state.
> 
> There is no real difference in performance because the current code already
> does a full restore when the xfeatures bits are preserved as the signal
> frame setup has stored them, which is the full UABI feature set.
> 
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> ---
>  arch/x86/kernel/fpu/signal.c |   92 +++++++++++++++----------------------------
>  1 file changed, 33 insertions(+), 59 deletions(-)

...

> @@ -390,54 +362,56 @@ static int __fpu_restore_sig(void __user
>  		set_thread_flag(TIF_NEED_FPU_LOAD);
>  	}
>  	__fpu_invalidate_fpregs_state(fpu);
> +	__cpu_invalidate_fpregs_state();
>  	fpregs_unlock();
>  
>  	if (use_xsave() && !fx_only) {
> -		u64 init_bv = xfeatures_mask_uabi() & ~user_xfeatures;
> -
> -		ret = copy_sigframe_from_user_to_xstate(&fpu->state.xsave, buf_fx);
> +		ret = copy_sigframe_from_user_to_xstate(&fpu->state.xsave,
> +							buf_fx);

Why? Just let it stick out.

Regardless,

Reviewed-by: Borislav Petkov <bp@xxxxxxx>

-- 
Regards/Gruss,
    Boris.

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