staging: vchiq: avoid mixing kernel and user pointers

staging: vchiq: avoid mixing kernel and user pointers

As found earlier, there is a problem in the create_pagelist() function
that takes a pointer argument that either points into vmalloc space or
into user space, with the pointer value controlled by user space allowing
a malicious user to trick the driver into accessing the kernel instead.

Avoid this problem by adding another function argument and passing
kernel pointers separately from user pointers. This makes it possible
to rely on sparse to point out invalid conversions, and it prevents
user space from faking a kernel pointer.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20200925114424.2647144-2-arnd@arndb.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>