On Thu, 2019-04-25 at 17:55 +0200, Arnd Bergmann wrote: > On Thu, Apr 25, 2019 at 5:35 PM Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > > > > On Thu, Apr 25, 2019 at 12:21:53PM -0300, Mauro Carvalho Chehab wrote: > > > > > If I understand your patch description well, using compat_ptr_ioctl > > > only works if the driver is not for s390, right? > > > > No; s390 is where "oh, just set ->compat_ioctl same as ->unlocked_ioctl > > and be done with that; compat_ptr() is a no-op anyway" breaks. IOW, > > s390 is the reason for having compat_ptr_ioctl() in the first place; > > that thing works on all biarch architectures, as long as all stuff > > handled by ->ioctl() takes pointer to arch-independent object as > > argument. IOW, > > argument ignored => OK > > any arithmetical type => no go, compat_ptr() would bugger it > > pointer to int => OK > > pointer to string => OK > > pointer to u64 => OK > > pointer to struct {u64 addr; char s[11];} => OK > > To be extra pedantic, the 'struct {u64 addr; char s[11];} ' > case is also broken on x86, because sizeof (obj) is smaller > on i386, even though the location of the members are > the same. i.e. you can copy_from_user() this Actually, you can't even do that because the struct might sit at the end of a page and then you'd erroneously fault in this case. We had this a while ago with struct ifreq, see commit 98406133dd and its parents. johannes