On Sun, Jul 04, 2021 at 01:41:51PM -0700, Linus Torvalds wrote: > On Sun, Jul 4, 2021 at 1:28 PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote: > > > > Turns out that, at least on m68k/nommu, USER_DS and KERNEL_DS are the same. > > > > #define USER_DS MAKE_MM_SEG(TASK_SIZE) > > #define KERNEL_DS MAKE_MM_SEG(0xFFFFFFFF) > > Ahh. So the code is fine, it's just that "uaccess_kernel()" isn't > something that can be reliably even tested for, and it will always > return true on those nommu platforms. Yes, I think m68knommu and armnommu have this problems. They really need to be converted to stop implementing set_fs ASAP, as there is no point for them. > And we don't have a "uaccess_user()" macro that would test if it > matches USER_DS (and that also would always return true on those > configurations), so we can't just change the > > WARN_ON_ONCE(uaccess_kernel()); > > into a > > WARN_ON_ONCE(!uaccess_user()); > > instead. > > Very annoying. Basically, every single use of "uaccess_kernel()" is unreliable. Yes. > The other alternative would be to just make nommu platforms that have > KERNEL_DS==USER_DS simply do > > #define uaccess_kernel() (false) > > and avoid it that way, since that's closer to what the modern > non-CONFIG_SET_FS world view is, and is what include/linux/uaccess.h > does for that case.. Maybe that is the best short-term bandaid.
