On Thu, May 26, 2016 at 03:50:01PM +0100, Szabolcs Nagy wrote: > On 26/05/16 15:20, Catalin Marinas wrote: > > While writing the above, I realised the current ILP32 patches still miss > > on converting pointers passed from user space (unless I got myself > > confused in macros). The new __SC_WRAP() and COMPAT_SYSCALL_WRAPx() > > macros take care of zero or sign extension via __SC_COMPAT_CAST(). > > However, we have two more existing cases which I don't see covered: > > > > a) Native syscalls taking a pointer argument and invoked directly from > > ILP32. For example, sys_read() takes a pointer but I don't see any > > __SC_WRAP added by patch 5 > > > > b) Current compat syscalls taking a pointer argument. For example, > > compat_sys_vmsplice() gets the iov32 pointer and the compiler assumes > > it is a 64-bit variable. I don't see where the upper half is zeroed > > on x32 sign/zero extension is currently left to userspace, > which is difficult to deal with, (long long)arg does the > wrong thing for pointer args. I agree, I don't think we should leave sign/zero extension to user. We should do it in the kernel either in a way similar to s390 (specific __SC_COMPAT_CAST, __SC_DELOUSE) or by always zeroing the arguments upper half on kernel entry with a few additional wrappers (where we have 64-bit arguments or they require sign extension). The latter has the disadvantage of having to split 64-bit arguments in user space while the former adds more maintenance burden to the kernel. I can't comment on performance aspects without some real numbers. -- Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
