On Mon 2019-06-10 08:47:45, Yu-cheng Yu wrote: > 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. Loading .so is already many syscalls, I'd not expect measurable performance there. Are you sure? Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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