As reported by Jeremy, 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 <jer...@jcline.org>
Signed-off-by: Ard Biesheuvel <ard.biesheu...@linaro.org>
---
 drivers/firmware/efi/libstub/tpm.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/firmware/efi/libstub/tpm.c 
b/drivers/firmware/efi/libstub/tpm.c
index da661bf8cb96..13c1edd37e96 100644
--- a/drivers/firmware/efi/libstub/tpm.c
+++ b/drivers/firmware/efi/libstub/tpm.c
@@ -68,11 +68,11 @@ void efi_retrieve_tpm2_eventlog_1_2(efi_system_table_t 
*sys_table_arg)
        efi_guid_t linux_eventlog_guid = LINUX_EFI_TPM_EVENT_LOG_GUID;
        efi_status_t status;
        efi_physical_addr_t log_location, log_last_entry;
-       struct linux_efi_tpm_eventlog *log_tbl;
+       struct linux_efi_tpm_eventlog *log_tbl = NULL;
        unsigned long first_entry_addr, last_entry_addr;
        size_t log_size, last_entry_size;
        efi_bool_t truncated;
-       void *tcg2_protocol;
+       void *tcg2_protocol = NULL;
 
        status = efi_call_early(locate_protocol, &tcg2_guid, NULL,
                                &tcg2_protocol);
-- 
2.15.1

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