Re: [PATCH v6 38/41] x86/fpu: Add helper for initing features

[Kees Cook]

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 <pengfei.xu@xxxxxxxxx>
> Tested-by: John Allen <john.allen@xxxxxxx>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

-- 
Kees Cook