efi/libstub/tpm: Initialize pointer variables to zero for mixed mode

efi/libstub/tpm: Initialize pointer variables to zero for mixed mode

As reported by Jeremy Cline, running the new TPM libstub code in mixed
mode (i.e., 64-bit kernel on 32-bit UEFI) results in hangs when invoking
the TCG2 protocol, or when accessing the log_tbl pool allocation.

The reason turns out to be that in both cases, the 64-bit pointer
variables are not fully initialized by the 32-bit EFI code, and so
we should take care to zero initialize these variables beforehand,
or we'll end up dereferencing bogus pointers.

Reported-by: Jeremy Cline <[email protected]>
Signed-off-by: Ard Biesheuvel <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>