On 10/26/23 15:13, Pawan Gupta wrote: >>>> Interrupts returning to kernel don't clear the CPU buffers. I believe >>>> interrupts will be enabled here, and getting an interrupt here could >>>> leak the data that interrupt touched. >>> Specifically NMIs, right? >> Yes, and VERW can omitted for the same reason as NMI returning to >> kernel. > Thinking more on this, we should not omit verw here, as this spot is way > easier to target NMIs. A user executing SYSENTER in a loop has much > higher chances of causing an NMI to return to kernel, and skip verw. Right. This is also a path where we care *ZERO* about performance. It's basically all upside to _add_ VERW and all downside (increased attack surface) to skip it.
