[edk2-devel] [PATCH RESEND 1/1] StandaloneMmPkg/Core: Remove optimization for depex evaluation

["Nhi Pham via groups.io" <nhi=os.amperecomputing.com@groups.io>]

From: Laszlo Ersek <lersek@redhat.com>

The current dependency evaluator violates the memory access permission
when patching depex grammar directly in the read-only depex memory area.

Laszlo pointed out the optimization issue in the thread (1) "Memory
Attribute for depex section" and provided suggested patch to remove the
perf optimization.

In my testing, removing the optimization does not make significant perf
reduction. That makes sense that StandaloneMM dispatcher only searches
in MM protocol database and does not depend on UEFI/DXE protocol
database. Also, we don't have many protocols in StandaloneMM like
UEFI/DXE.

From Laszlo,

"The patch removes the EFI_DEP_REPLACE_TRUE handling altogether, plus it
CONST-ifies the Iterator pointer (which points into the DEPEX section),
so that the compiler catch any possible accesses at *build time* that
would write to the write-protected DEPEX memory area."

(1) https://edk2.groups.io/g/devel/message/113531

Signed-off-by: Nhi Pham <nhi@os.amperecomputing.com>
Tested-by: levi.yun <yeoreum.yun@arm.com>
Reviewed-by: levi.yun <yeoreum.yun@arm.com>
---
 StandaloneMmPkg/Core/Dependency.c | 37 ++++----------------
 1 file changed, 7 insertions(+), 30 deletions(-)

diff --git a/StandaloneMmPkg/Core/Dependency.c b/StandaloneMmPkg/Core/Dependency.c
index 440fe3e45238..2bcb07d34666 100644
--- a/StandaloneMmPkg/Core/Dependency.c
+++ b/StandaloneMmPkg/Core/Dependency.c
@@ -13,16 +13,6 @@
 
 #include "StandaloneMmCore.h"
 
-///
-/// EFI_DEP_REPLACE_TRUE - Used to dynamically patch the dependency expression
-///                        to save time.  A EFI_DEP_PUSH is evaluated one an
-///                        replaced with EFI_DEP_REPLACE_TRUE. If PI spec's Vol 2
-///                        Driver Execution Environment Core Interface use 0xff
-///                        as new DEPEX opcode. EFI_DEP_REPLACE_TRUE should be
-///                        defined to a new value that is not conflicting with PI spec.
-///
-#define EFI_DEP_REPLACE_TRUE  0xff
-
 ///
 /// Define the initial size of the dependency expression evaluation stack
 ///
@@ -170,12 +160,12 @@ MmIsSchedulable (
   IN  EFI_MM_DRIVER_ENTRY  *DriverEntry
   )
 {
-  EFI_STATUS  Status;
-  UINT8       *Iterator;
-  BOOLEAN     Operator;
-  BOOLEAN     Operator2;
-  EFI_GUID    DriverGuid;
-  VOID        *Interface;
+  EFI_STATUS   Status;
+  CONST UINT8  *Iterator;
+  BOOLEAN      Operator;
+  BOOLEAN      Operator2;
+  EFI_GUID     DriverGuid;
+  VOID         *Interface;
 
   Operator  = FALSE;
   Operator2 = FALSE;
@@ -253,8 +243,7 @@ MmIsSchedulable (
           Status = PushBool (FALSE);
         } else {
           DEBUG ((DEBUG_DISPATCH, "  PUSH GUID(%g) = TRUE\n", &DriverGuid));
-          *Iterator = EFI_DEP_REPLACE_TRUE;
-          Status    = PushBool (TRUE);
+          Status = PushBool (TRUE);
         }
 
         if (EFI_ERROR (Status)) {
@@ -356,18 +345,6 @@ MmIsSchedulable (
         DEBUG ((DEBUG_DISPATCH, "  RESULT = %a\n", Operator ? "TRUE" : "FALSE"));
         return Operator;
 
-      case EFI_DEP_REPLACE_TRUE:
-        CopyMem (&DriverGuid, Iterator + 1, sizeof (EFI_GUID));
-        DEBUG ((DEBUG_DISPATCH, "  PUSH GUID(%g) = TRUE\n", &DriverGuid));
-        Status = PushBool (TRUE);
-        if (EFI_ERROR (Status)) {
-          DEBUG ((DEBUG_DISPATCH, "  RESULT = FALSE (Unexpected error)\n"));
-          return FALSE;
-        }
-
-        Iterator += sizeof (EFI_GUID);
-        break;
-
       default:
         DEBUG ((DEBUG_DISPATCH, "  RESULT = FALSE (Unknown opcode)\n"));
         goto Done;
-- 
2.25.1



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