Re: [PATCH 08/10] x86/xsaves: Fix PTRACE frames for XSAVES

[Dave Hansen]

On 02/22/2016 11:00 AM, Yu-cheng Yu wrote:
> +	if (xsave->header.xfeatures & XFEATURE_MASK_SUPERVISOR)
> +		xsave->header.xfeatures = xfeatures | XFEATURE_MASK_SUPERVISOR;
> +	else
> +		xsave->header.xfeatures = xfeatures;

This is dangerous.  It says, "if any supervisor feature bit is set, then
set *ALL* of the known bits".  There's no way that can work.

Don't you just want to or in the new bits that were in the passed-in
'xfeatures':

	xsave->header.xfeatures |= xfeatures;

'xfeatures' is known not to contain any supervisor bits.