On Thu, Jun 28, 2018 at 11:27:42AM +0100, Catalin Marinas wrote: > On Thu, Jun 28, 2018 at 08:17:59AM +0200, Luc Van Oostenryck wrote: > > On Wed, Jun 27, 2018 at 06:17:58PM +0100, Catalin Marinas wrote: > > > sparse is indeed an option. The current implementation doesn't warn on > > > an explicit cast from (void __user *) to (unsigned long) since that's a > > > valid thing in the kernel. I couldn't figure out if there's any other > > > __attribute__ that could be used to warn of such conversion. > > > > sparse doesn't have such attribute but would an new option that would warn > > on such cast be a solution for your case? > > I can't tell for sure whether such sparse option would be the full > solution but detecting explicit __user pointer casts to long is a good > starting point. So far this patchset pretty much relies on detecting > a syscall failure and trying to figure out why, patching the kernel. It > doesn't really scale. OK, I'll add such an option this evening. > As a side note, we have cases in the user-kernel ABI where the user > address type is "unsigned long": mmap() and friends. My feedback on an > early version of this patchset was to always require untagged pointers > coming from user space on such syscalls, so no need for explicit > untagging. Mmmm yes. I tend to favor a sort of opposite approach. When we have an address that must not be dereferenced as-such (and sometimes when the address can be from both __user & __kernel space) I prefer to use a ulong which will force the use of the required operation before being able to do any sort of dereferencing and this won't need horrible casts with __force (it, of course, all depends on the full context). -- Luc
