Ok, firstly - SSDT stands for System Service Descriptor Table, so you can't 'tell' it to do something and it doesn't 'provide' information except for adresses of kernel syscalls - are you sure you know what you're writing about?
All of kernel memory (0x80000000 and above on 32-bit systems) is shared between different processes, so once some data is copied there, it doesn't matter which process' pagetable we're currently using.
FYI, all syscalls are expected to copy memory to kernelspace prior to doing something with them - so as to prevent race condition between syscalls running on IRQL lower than DISPATCH_LEVEL and for instance userspace code - just imagine, if this was happening, process could call OpenProcess on something it can access, then try to race with it to gain access to winlogon.exe. THIS IS NOT THE CASE - you can try it, coding it is just a few while loops.
For your information, all userspace<->kernelspace memory copying routines do their job at at least DISPATCH_LEVEL, which means they cannot be pre-empted. Even Microsoft's own docs state that you should always capture the user-space buffer because of possible race condition (see here: http://download.microsoft.com/download/D/1/D/D1DD7745-426B-4CC3-A269-ABBBE427C0EF/SYS-T774_DDC08.pptx ), so this bug means that people implementing the syscall filters failed to understand what this document says - that is, for all processing in kernel mode, the data should be copied into the kernel space AT THE BEGINNING and at one point only, processed and then returned to user, also in ONE POINT. What the AV vendors did was just pure laziness, I presume.