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

[Andy Lutomirski]

On Fri, Sep 18, 2020 at 8:16 AM Christoph Hellwig <hch at lst.de> wrote:
>
> On Fri, Sep 18, 2020 at 02:58:22PM +0100, Al Viro wrote:
> > 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...
>
> That would help to not introduce a regression with this series yes.
> But it wouldn't fix existing bugs when io_uring is used to access
> read or write methods that use in_compat_syscall().  One example that
> I recently ran into is drivers/scsi/sg.c.

Aside from the potentially nasty use of per-task variables, one thing
I don't like about PF_FORCE_COMPAT is that it's one-way.  If we're
going to have a generic mechanism for this, shouldn't we allow a full
override of the syscall arch instead of just allowing forcing compat
so that a compat syscall can do a non-compat operation?