Re: [PATCH v5 04/27] x86/fpu/xstate: Add XSAVES system states for shadow stack

On 11/8/18 1:22 PM, Andy Lutomirski wrote:

quoted

+struct cet_kernel_state {
+       u64 kernel_ssp; /* kernel shadow stack */
+       u64 pl1_ssp;    /* ring-1 shadow stack */
+       u64 pl2_ssp;    /* ring-2 shadow stack */
+} __packed;
+

Why are these __packed?  It seems like it'll generate bad code for no
obvious purpose.

It's a hardware-defined in-memory structure.  Granted, we'd need a
really wonky compiler to make that anything *other* than a nicely-packed
24-byte structure, but the __packed makes it explicit.

It is probably a really useful long-term thing to stop using __packed
and start using "__hw_defined" or something that #defines down to __packed.