[PATCH] efi_loader: Check for pointers before appending to the eventlog

[Ilias Apalodimas]

The TCG protocol returns EFI_SUCCESS even when it fails to install.
If the protocol is not installed there should be no calls to
tcg2_agile_log_append().  However there are calls to this function
occurring outside the TCG protocol invocation (e.g tcg2_measure_pe_image).

Let's deal with this and shield the code from crashing while complaining,
so buggy code can be spotted and fixed.

Signed-off-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
---
Heinrich this is rebased on top of https://lore.kernel.org/u-boot/20211123115335.125252-1-ruchika.gupta@linaro.org/
 lib/efi_loader/efi_tcg2.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/lib/efi_loader/efi_tcg2.c b/lib/efi_loader/efi_tcg2.c
index 133fe8291a92..57a1f37695f6 100644
--- a/lib/efi_loader/efi_tcg2.c
+++ b/lib/efi_loader/efi_tcg2.c
@@ -311,6 +311,17 @@ static efi_status_t tcg2_agile_log_append(u32 pcr_index, u32 event_type,
 	struct efi_tcg2_final_events_table *final_event;
 	efi_status_t ret = EFI_SUCCESS;
 
+	/*
+	 * This should never happen.  This function should only be invoked if
+	 * the TCG2 protocol has been installed.  However since we always
+	 * return EFI_SUCCESS from efi_tcg2_register shield callers against
+	 * crashing and complain
+	 */
+	if (!event_log.final_buffer || !event_log.buffer) {
+		log_err("EFI TCG2 protocol not installed\n");
+		return EFI_INVALID_PARAMETER;
+	}
+
 	/* if ExitBootServices hasn't been called update the normal log */
 	if (!event_log.ebs_called) {
 		if (event_log.truncated ||
-- 
2.34.0