From: Al Viro > Sent: 18 September 2020 14:58 > > On Fri, Sep 18, 2020 at 03:44:06PM +0200, Christoph Hellwig wrote: > > On Fri, Sep 18, 2020 at 02:40:12PM +0100, Al Viro wrote: > > > > /* Vector 0x110 is LINUX_32BIT_SYSCALL_TRAP */ > > > > - return pt_regs_trap_type(current_pt_regs()) == 0x110; > > > > + return pt_regs_trap_type(current_pt_regs()) == 0x110 || > > > > + (current->flags & PF_FORCE_COMPAT); > > > > > > Can't say I like that approach ;-/ Reasoning about the behaviour is much > > > harder when it's controlled like that - witness set_fs() shite... > > > > I don't particularly like it either. But do you have a better idea > > how to deal with io_uring vs compat tasks? > > <wry> git rm fs/io_uring.c would make a good starting point </wry> > Yes, I know it's not going to happen, but one can dream... Maybe the io_uring code needs some changes to make it vaguely safe. - No support for 32-bit compat mixed working (or at all?). Plausibly a special worker could do 32bit work. - ring structure (I'm assuming mapped by mmap()) never mapped in more than one process (not cloned by fork()). - No implicit handover of files to another process. Would need an munmap, handover, mmap sequence. In any case the io_ring rather abuses the import_iovec() interface. The canonical sequence is (types from memory): struct iovec cache[8], *iov = cache; struct iter iter; ... rval = import_iovec(..., &iov, 8, &iter); // Do read/write user using 'iter' free(iov); I don't think there is any strict requirement that iter.iov is set to either 'cache' or 'iov' (it probably must point into one of them.) But the io_uring code will make that assumption because the actual copies can be done much later and it doesn't save 'iter'. It gets itself in a right mess because it doesn't separate the 'address I need to free' from 'the iov[] for any transfers'. io_uring is also the only code that relies on import_iovec() returning the iter.count on success. It would be much better to have: iov = import_iovec(..., &cache, ...); free(iov); and use ERR_PTR() et al for error detectoion. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
