On 6/7/19 10:43 AM, Peter Zijlstra wrote: > I've no idea what the kernel should do; since you failed to answer the > question what happens when you point this to garbage. > > Does it then fault or what? Yeah, I think you'll fault with a rather mysterious CR2 value since you'll go look at the instruction that faulted and not see any references to the CR2 value. I think this new MSR probably needs to get included in oops output when CET is enabled. Why don't we require that a VMA be in place for the entire bitmap? Don't we need a "get" prctl function too in case something like a JIT is running and needs to find the location of this bitmap to set bits itself? Or, do we just go whole-hog and have the kernel manage the bitmap itself. Our interface here could be: prctl(PR_MARK_CODE_AS_LEGACY, start, size); and then have the kernel allocate and set the bitmap for those code locations.
