efistub/tpm: Use ACPI reclaim memory for event log to avoid corruption

The TPM event log table is a Linux specific construct, where the data
produced by the GetEventLog() boot service is cached in memory, and
passed on to the OS using an EFI configuration table.

The use of EFI_LOADER_DATA here results in the region being left
unreserved in the E820 memory map constructed by the EFI stub, and this
is the memory description that is passed on to the incoming kernel by
kexec, which is therefore unaware that the region should be reserved.

Even though the utility of the TPM2 event log after a kexec is
questionable, any corruption might send the parsing code off into the
weeds and crash the kernel. So let's use EFI_ACPI_RECLAIM_MEMORY
instead, which is always treated as reserved by the E820 conversion
logic.

Cc: <stable@vger.kernel.org>
Reported-by: Breno Leitao <leitao@debian.org>
Tested-by: Usama Arif <usamaarif642@gmail.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

drivers/firmware/efi/libstub/tpm.c

@@ -96,7 +96,7 @@ static void efi_retrieve_tcg2_eventlog(int version, efi_physical_addr_t log_loca
 	}
 
 	/* Allocate space for the logs and copy them. */
-	status = efi_bs_call(allocate_pool, EFI_LOADER_DATA,
+	status = efi_bs_call(allocate_pool, EFI_ACPI_RECLAIM_MEMORY,
 			     sizeof(*log_tbl) + log_size, (void **)&log_tbl);
 
 	if (status != EFI_SUCCESS) {