From e10ad1c8748db6f886be57f98137355e4abbcb31 Mon Sep 17 00:00:00 2001
From: Matt DeVillier <matt.devillier@gmail.com>
Date: Tue, 17 Mar 2020 13:34:40 -0500
Subject: [PATCH] MdeModulePkg/EmuRuntimeDxe: skip console NVRAM variables

Tianocore currently reads/writes a lot of NVRAM variables that
don't actually need to be saved. Occasionally some, specifically
related to the graphical/serial consoles, can become corrupted,
leading to a bricked device. To avoid this, temporarily restrict
the reading/writing of variables to skip console related ones
(starting with 'Con') until a better solution can be found.

Test: build/boot google/eve, inject "bad" NVRAM data, observe
device boots normally instead of hanging with no display detected.

Signed-off-by: Matt DeVillier <matt.devillier@gmail.com>
---
 .../Variable/EmuRuntimeDxe/EmuVariable.c      | 39 +++++++++++--------
 1 file changed, 22 insertions(+), 17 deletions(-)

diff --git a/MdeModulePkg/Universal/Variable/EmuRuntimeDxe/EmuVariable.c b/MdeModulePkg/Universal/Variable/EmuRuntimeDxe/EmuVariable.c
index 1febc66226..0b1aa3b0b8 100644
--- a/MdeModulePkg/Universal/Variable/EmuRuntimeDxe/EmuVariable.c
+++ b/MdeModulePkg/Universal/Variable/EmuRuntimeDxe/EmuVariable.c
@@ -1100,13 +1100,14 @@ UpdateVariable (
 Store:
   // If the store is initialized
   // And we are storing or deleting a non volatile variable
+  // And variable name doesn't start with  'Con'
   // Send the new data to SMMSTORE
   if (storeInitialized && (
       (Attributes & EFI_VARIABLE_NON_VOLATILE) != 0 || (
         Delete &&
         (Variable->CurrPtr->Attributes & EFI_VARIABLE_NON_VOLATILE) != 0
-      )
-    )) {
+      )) && (StrnCmp(L"Con", VariableName, StrLen(L"Con")))
+    ) {
 
     /* TODO: add hook for logging nv changes here */
 
@@ -1978,23 +1979,27 @@ VariableCommonInitialize (
       EFI_GUID *guid = (EFI_GUID *)(buf + i + 8);
       VOID *data = (VOID *)(buf + i + 8 + keysz);
 
-      DEBUG ((DEBUG_WARN, "Fetching variable: %s\n", varname));
-      DEBUG ((DEBUG_WARN, "buf: %p, buf+i: %p, guid: %p, varname: %p, data: %p\n", buf, buf + i, guid, varname, data));
-      VARIABLE_POINTER_TRACK Variable;
-      FindVariable (varname, guid, &Variable, (VARIABLE_GLOBAL *)mVariableModuleGlobal);
+      // don't update console variables 
+      if (StrnCmp(L"Con", varname, StrLen(L"Con"))) {
+        DEBUG ((DEBUG_WARN, "Fetching variable: %s\n", varname));
+        DEBUG ((DEBUG_WARN, "buf: %p, buf+i: %p, guid: %p, varname: %p, data: %p\n", buf, buf + i, guid, varname, data));
+        VARIABLE_POINTER_TRACK Variable;
+        FindVariable (varname, guid, &Variable, (VARIABLE_GLOBAL *)mVariableModuleGlobal);
 
-      DEBUG ((DEBUG_WARN, "Updating variable: %s\n", varname));
-      UpdateVariable (
-        varname,
-	      guid,
-	      data,
-        valsz,
-	      // all of these variables are nv
-        EFI_VARIABLE_NON_VOLATILE | EFI_VARIABLE_BOOTSERVICE_ACCESS | EFI_VARIABLE_RUNTIME_ACCESS,
-        &Variable
-      );
+        DEBUG ((DEBUG_WARN, "Updating variable: %s\n", varname));
+        UpdateVariable (
+          varname,
+          guid,
+          data,
+          valsz,
+          // all of these variables are nv
+          EFI_VARIABLE_NON_VOLATILE | EFI_VARIABLE_BOOTSERVICE_ACCESS | EFI_VARIABLE_RUNTIME_ACCESS,
+          &Variable
+        );
+      } else {
+        DEBUG ((DEBUG_WARN, "Skipping console variable: %s\n", varname));
+      }
     }
-    DEBUG ((DEBUG_WARN, "Added variable: 0x%x, val size: %x\n", keysz, valsz));
     // no UEFI variable since it's at most the GUID part, so skip
     i += 8 + keysz + valsz + 1;
     i = (i + 3) & ~3;