Re: [PATCH] fs/binfmt_elf.c: allocate initialized memory in fill_thread_core_info()

[Al Viro]

On Wed, May 13, 2020 at 04:33:49AM +0100, Al Viro wrote:

> FWIW, what I'm going to do is
> 	* make all callers of copy_regset_to_user() pass 0 as pos
> (there are very few exceptions - one on arm64, three on sparc32
> and five on sparc64; I hadn't dealt with arm64 one yet, but all
> cases on sparc are handled)

[snip]

Any of that would be easy to backport, though.  Several questions
regaring XSAVE and friends:

* do we ever run on XSAVE/XSAVES-capable hardware with XFEATURE_FP
turned off?

* is it possible for x86 to have gaps between the state components
area as reported by CPUID 0x0d?  IOW, can area for feature 2
(XFEATURE_YMM) to start *not* at 0x200 and can area for N start
not right after the end of area for N-1 for some N > 2?

I think I have an easy-to-backport solution, but I'm really confused
about XFEATURE_FP situation...