[PATCH 1/1] efi/libstub/tpm: Initialize efi_physical_addr_t vars to zero for mixed mode

[Ard Biesheuvel]

From: Hans de Goede <hdegoede@xxxxxxxxxx>

Commit 79832f0b5f71 ("efi/libstub/tpm: Initialize pointer variables to zero
for mixed mode") fixes a problem with the tpm code on mixed mode (64 bit
kernel on 32 bit UEFI), where 64-bit pointer variables are not fully
initialized by the 32-bit EFI code.

A similar problem applies to the efi_physical_addr_t variables which
are written by the get_event_log EFI call. Even though efi_physical_addr_t
is 64 bit everywhere it seems that some 32 bit UEFI implementations only
fill in the lower 32 bits when passed a pointer to an efi_physical_addr_t
to fill.

This commit initializes these to 0 to, to ensure the upper 32 bits are
0 in mixed mode. This fixes recent kernels sometimes hanging during
early boot on mixed mode UEFI systems.

Cc: <stable@xxxxxxxxxxxxxxx> # v4.16+
Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
---
 drivers/firmware/efi/libstub/tpm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/libstub/tpm.c b/drivers/firmware/efi/libstub/tpm.c
index caa37a6dd9d4..a90b0b8fc69a 100644
--- a/drivers/firmware/efi/libstub/tpm.c
+++ b/drivers/firmware/efi/libstub/tpm.c
@@ -64,7 +64,7 @@ static void efi_retrieve_tpm2_eventlog_1_2(efi_system_table_t *sys_table_arg)
 	efi_guid_t tcg2_guid = EFI_TCG2_PROTOCOL_GUID;
 	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;
+	efi_physical_addr_t log_location = 0, log_last_entry = 0;
 	struct linux_efi_tpm_eventlog *log_tbl = NULL;
 	unsigned long first_entry_addr, last_entry_addr;
 	size_t log_size, last_entry_size;
-- 
2.17.1