On Sat, Feb 18, 2023 at 01:14:30PM -0800, Rick Edgecombe wrote:

If an xfeature is saved in a buffer, the xfeature's bit will be set in
xsave->header.xfeatures. The CPU may opt to not save the xfeature if it
is in it's init state. In this case the xfeature buffer address cannot
be retrieved with get_xsave_addr().

Future patches will need to handle the case of writing to an xfeature
that may not be saved. So provide helpers to init an xfeature in an
xsave buffer.

This could of course be done directly by reaching into the xsave buffer,
however this would not be robust against future changes to optimize the
xsave buffer by compacting it. In that case the xsave buffer would need
to be re-arranged as well. So the logic properly belongs encapsulated
in a helper where the logic can be unified.

Tested-by: Pengfei Xu <redacted>
Tested-by: John Allen <john.allen@amd.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>

Reviewed-by: Kees Cook <redacted>

-- 
Kees Cook