On Thu, Jul 30, 2020 at 11:18:04AM +0200, Arnd Bergmann wrote:

On Thu, Jul 30, 2020 at 10:38 AM Andy Shevchenko
[off-list ref] wrote:

quoted

On Thu, Jul 30, 2020 at 10:15:24AM +0200, Arnd Bergmann wrote:

quoted

On Thu, Jul 30, 2020 at 10:07 AM Bartosz Golaszewski [off-list ref] wrote:

...

quoted

quoted

I would argue that it needs to be fixed anyway, unless you also want
to remove the v1 interface for native mode. If this works on 32-bit
kernels, on 64-bit kernels with 64-bit user space and on compat
32-bit user space on 64-bit non-x86 architectures, I see no reason
to leave it broken specifically on x86 compat user space. There are
still reasons to use 32-bit x86 user space for low-memory machines
even though native i386 kernels are getting increasingly silly.

It was possible to "fix" (mitigate to some extent) before libgpiod got support
for several events in a request. Now it seems to be impossible to fix. AFAIU we
must discard any request to more than one event in it.

Any reason why the workaround I suggested above would not work?

That is the question to somebody who has better understanding. If it works,
I vote up to get it fixed with little effort. I would be glad to test patches!

The in_ia32_syscall() check should be completely reliable in telling whether
we are called from read() by an ia32 task or not, and we use the same
logic for input_event, which has a similar problem (on all compat architectures,
not just x86).

By the way any reason why we have to have in_ia32_syscall() instead of
in_compat_syscall()?

quoted

However I'm not an expert in compat IOCTL code (you are :-) and perhaps you may
provide ideas better than mine.

What makes this interface tricky is that this is actually a read() call, not
ioctl() which is usually easier because it encodes the data length in the
command code. As far as I could tell from skimming the interface, the
ioctls are actually fine here.

Right.

-- 
With Best Regards,
Andy Shevchenko


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