Re: [PATCH] x86/fpu: move FPU state into separate cache

[Andy Lutomirski]

On Wed, Mar 29, 2017 at 2:30 PM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Wed, Mar 29, 2017 at 2:09 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>>
>> They're adjacent already, which poses a problem for the struct layout
>> randomization plugin, since adjacency may no longer be true (after
>> layout randomization). T
>
> What?
>
> The layout randomization can't change anything, if you just make the
> adjacency be done explicitly instead of by having the thing be a fixed
> member.
>
> The trivial model might be to just declare the fpu part as an unsized
> array at the end:
>
>         /* Floating point and extended processor state */
>         struct fpu              fpu[];
>
> because there is no way in hell that any randomization code can move
> those kinds of unsized arrays around. If it does, the gcc plugin is
> such unbelievable garbage that it would be insane to depend on such
> shit in the first place.
>

Randomization also needs to leave thread_info at the beginning.  Can it do that?