[edk2-devel][PATCH v1 1/1] ArmPkg: DefaultExceptionHandlerLib: Do Not Allocate\r Memory

["Oliver Smith-Denny" <osde@linux.microsoft.com>]

If gST->ConOut is available when Arm's DefaultExceptionHandler
is running, AsciiPrint will get called to attempt to print to
ConOut, in addition to the serial output.

AsciiPrint calls AsciiInternalPrint in UefiLibPrint.c which
in turn calls AllocatePool to allocate a buffer to convert
the Ascii input string to a Unicode string to pass to
ConOut->OutputString.

Per the comment on DefaultExceptionHandler, we should not be
allocating memory in the exception handler, as this can cause
the exception handler to fail if we had a memory exception or
the system state is such that we cannot allocate memory.

It has been observed on ArmVirtQemu that exceptions generated
in the memory handling code will fail to output the stack dump
and CPU state that is critical to debugging because the
AllocatePool will fail.

This patch fixes the Arm and AARCH64 DefaultExceptionHandlers to
not allocate memory when ConOut is available and instead use
stack memory to convert the Ascii string needed for SerialPortWrite
to the Unicode string needed for ConOut->OutputString. Correspondingly,
ArmVirtQemu can now output the stack dump and CPU state when hitting
an exception in memory code.

GitHub PR: https://github.com/tianocore/edk2/pull/4703

Cc: Leif Lindholm <quic_llindhol@quicinc.com>
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Sami Mujawar <sami.mujawar@arm.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>

Signed-off-by: Oliver Smith-Denny <osde@linux.microsoft.com>
---
 ArmPkg/Library/DefaultExceptionHandlerLib/AArch64/DefaultExceptionHandler.c | 18 +++++++++++++-----
 ArmPkg/Library/DefaultExceptionHandlerLib/Arm/DefaultExceptionHandler.c     | 11 +++++++++--
 2 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/ArmPkg/Library/DefaultExceptionHandlerLib/AArch64/DefaultExceptionHandler.c b/ArmPkg/Library/DefaultExceptionHandlerLib/AArch64/DefaultExceptionHandler.c
index f2bca5d74005..07c8aade1c5f 100644
--- a/ArmPkg/Library/DefaultExceptionHandlerLib/AArch64/DefaultExceptionHandler.c
+++ b/ArmPkg/Library/DefaultExceptionHandlerLib/AArch64/DefaultExceptionHandler.c
@@ -22,6 +22,11 @@
 #include <Protocol/DebugSupport.h>
 #include <Protocol/LoadedImage.h>
 
+//
+// Maximum number of characters to print to serial (UINT8s) and to console if available (as UINT16s)
+//
+#define MAX_PRINT_CHARS  100
+
 STATIC CHAR8  *gExceptionTypeString[] = {
   "Synchronous",
   "IRQ",
@@ -188,16 +193,18 @@ DefaultExceptionHandler (
   IN OUT EFI_SYSTEM_CONTEXT  SystemContext
   )
 {
-  CHAR8  Buffer[100];
-  UINTN  CharCount;
-  INT32  Offset;
+  CHAR8   Buffer[MAX_PRINT_CHARS];
+  CHAR16  UnicodeBuffer[MAX_PRINT_CHARS];
+  UINTN   CharCount;
+  INT32   Offset;
 
   if (mRecursiveException) {
     STATIC CHAR8 CONST  Message[] = "\nRecursive exception occurred while dumping the CPU state\n";
 
     SerialPortWrite ((UINT8 *)Message, sizeof Message - 1);
     if (gST->ConOut != NULL) {
-      AsciiPrint (Message);
+      UnicodeSPrintAsciiFormat (UnicodeBuffer, MAX_PRINT_CHARS, Buffer);
+      gST->ConOut->OutputString (gST->ConOut, UnicodeBuffer);
     }
 
     CpuDeadLoop ();
@@ -208,7 +215,8 @@ DefaultExceptionHandler (
   CharCount = AsciiSPrint (Buffer, sizeof (Buffer), "\n\n%a Exception at 0x%016lx\n", gExceptionTypeString[ExceptionType], SystemContext.SystemContextAArch64->ELR);
   SerialPortWrite ((UINT8 *)Buffer, CharCount);
   if (gST->ConOut != NULL) {
-    AsciiPrint (Buffer);
+    UnicodeSPrintAsciiFormat (UnicodeBuffer, MAX_PRINT_CHARS, Buffer);
+    gST->ConOut->OutputString (gST->ConOut, UnicodeBuffer);
   }
 
   DEBUG_CODE_BEGIN ();
diff --git a/ArmPkg/Library/DefaultExceptionHandlerLib/Arm/DefaultExceptionHandler.c b/ArmPkg/Library/DefaultExceptionHandlerLib/Arm/DefaultExceptionHandler.c
index 13b321e45615..08d62c0dbfa2 100644
--- a/ArmPkg/Library/DefaultExceptionHandlerLib/Arm/DefaultExceptionHandler.c
+++ b/ArmPkg/Library/DefaultExceptionHandlerLib/Arm/DefaultExceptionHandler.c
@@ -23,6 +23,11 @@
 #include <Protocol/DebugSupport.h>
 #include <Library/DefaultExceptionHandlerLib.h>
 
+//
+// Maximum number of characters to print to serial (UINT8s) and to console if available (as UINT16s)
+//
+#define MAX_PRINT_CHARS  100
+
 //
 // The number of elements in a CHAR8 array, including the terminating NUL, that
 // is meant to hold the string rendering of the CPSR.
@@ -198,7 +203,8 @@ DefaultExceptionHandler (
   IN OUT EFI_SYSTEM_CONTEXT  SystemContext
   )
 {
-  CHAR8    Buffer[100];
+  CHAR8    Buffer[MAX_PRINT_CHARS];
+  CHAR16   UnicodeBuffer[MAX_PRINT_CHARS];
   UINTN    CharCount;
   UINT32   DfsrStatus;
   UINT32   IfsrStatus;
@@ -217,7 +223,8 @@ DefaultExceptionHandler (
                 );
   SerialPortWrite ((UINT8 *)Buffer, CharCount);
   if (gST->ConOut != NULL) {
-    AsciiPrint (Buffer);
+    UnicodeSPrintAsciiFormat (UnicodeBuffer, MAX_PRINT_CHARS, Buffer);
+    gST->ConOut->OutputString (gST->ConOut, UnicodeBuffer);
   }
 
   DEBUG_CODE_BEGIN ();
-- 
2.40.1



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