On Sat, 2019-06-08 at 22:52 +0200, Pavel Machek wrote: > Hi! > > > > 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. > > For the record, that sounds like a better interface than userspace knowing > about the bitmap formats... > Pavel Initially we implemented the bitmap that way. To manage the bitmap, every time the application issues a syscall for a .so it loads, and the kernel does copy_from_user() & copy_to_user() (or similar things). If a system has a few legacy .so files and every application does the same, it can take a long time to boot up. Yu-cheng
