Messages in this thread | | | From | Arnd Bergmann <> | Date | Sat, 19 Sep 2020 23:16:10 +0200 | Subject | Re: [PATCH 1/9] kernel: add a PF_FORCE_COMPAT flag |
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On Sat, Sep 19, 2020 at 6:21 PM Andy Lutomirski <luto@kernel.org> wrote: > On Fri, Sep 18, 2020 at 8:16 AM Christoph Hellwig <hch@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.
Ah, so reading /dev/input/event* would suffer from the same issue, and that one would in fact be broken by your patch in the hypothetical case that someone tried to use io_uring to read /dev/input/event on x32...
For reference, I checked the socket timestamp handling that has a number of corner cases with time32/time64 formats in compat mode, but none of those appear to be affected by the problem.
> 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?
The only reason it's needed here is that the caller is in a kernel thread rather than a system call. Are there any possible scenarios where one would actually need the opposite?
Arnd
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