Re: [PATCH 1/9] kernel: add a PF_FORCE_COMPAT flag

Al Viro
2020-09-18T13:58:36Z

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...

Said that, why not provide a variant that would take an explicit
"is it compat" argument and use it there? And have the normal
one pass in_compat_syscall() to that...