On Tue, May 9, 2017 at 9:00 AM, Andy Lutomirski <luto@xxxxxxxxxx> wrote: > On Tue, May 9, 2017 at 1:56 AM, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: >> On Tue, May 09, 2017 at 08:45:22AM +0200, Ingo Molnar wrote: >>> We only have ~115 code blocks in the kernel that set/restore KERNEL_DS, it would >>> be a pity to add a runtime check to every system call ... >> >> I think we should simply strive to remove all of them that aren't >> in core scheduler / arch code. Basically evetyytime we do the >> >> oldfs = get_fs(); >> set_fs(KERNEL_DS); >> .. >> set_fs(oldfs); >> >> trick we're doing something wrong, and there should always be better >> ways to archive it. E.g. using iov_iter with a ITER_KVEC type >> consistently would already remove most of them. > > How about trying to remove all of them? If we could actually get rid > of all of them, we could drop the arch support, and we'd get faster, > simpler, shorter uaccess code throughout the kernel. > > The ones in kernel/compat.c are generally garbage. They should be > using compat_alloc_user_space(). Ditto for kernel/power/user.c. compat_alloc_user_space() is a hack that should go away too. It ends up copying the data three times. The more efficient solution to this is to have a core syscall function that only accesses kernel memory, and then have two front-end functions (native and compat) that do the actual reads and writes to userspace, with conversion in the compat case. -- Brian Gerst -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
