OcAppleKernelLib: Fix relocation support for EfiBoot in KC mode

huytbt · Jul 5, 2020 · 2705377 · 2705377
1 parent 1a71973
commit 2705377
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Showing 3 changed files with 96 additions and 7 deletions.
diff --git a/Docs/Sample.plist b/Docs/Sample.plist
@@ -574,6 +574,34 @@
 				<key>Skip</key>
 				<integer>0</integer>
 			</dict>
+			<dict>
+				<key>Base</key>
+				<string>_vstart</string>
+				<key>Comment</key>
+				<string>Print K and dead loop</string>
+				<key>Count</key>
+				<integer>1</integer>
+				<key>Enabled</key>
+				<false/>
+				<key>Find</key>
+				<data></data>
+				<key>Identifier</key>
+				<string>kernel</string>
+				<key>Limit</key>
+				<integer>0</integer>
+				<key>Mask</key>
+				<data></data>
+				<key>MaxKernel</key>
+				<string></string>
+				<key>MinKernel</key>
+				<string></string>
+				<key>Replace</key>
+				<data>sUtmuv0D7KggdPtmuvgDiMjusQpmuv0D7KggdPtmuvgDiMju6/6Q</data>
+				<key>ReplaceMask</key>
+				<data></data>
+				<key>Skip</key>
+				<integer>0</integer>
+			</dict>
 		</array>
 		<key>Quirks</key>
 		<dict>

diff --git a/Library/OcAppleKernelLib/KernelCollection.c b/Library/OcAppleKernelLib/KernelCollection.c
@@ -144,6 +144,44 @@ InternalKcWriteCommandHeaders (
   //
   MachHeader->NumCommands++;
   MachHeader->CommandsSize += sizeof (MACH_SEGMENT_COMMAND_64);
+
+  //
+  // Proceed to the next command.
+  //
+  Command.Address += Command.FilesetEntry->CommandSize;
+
+  //
+  // Write new __PRELINKED_INFO segment, as the first writeable segment is used by EfiBoot
+  // as a relocation base. Relocation in KC mode is very simplified, and this segment PADDR
+  // is simply used for all the relocations in DYSYMTAB. Unless we leave it untouched, sliding
+  // will "relocate" invalid memory, as new plist is normally put at the end of KC memory.
+  //
+  // Note, that we might need to resolve Context->PrelinkedInfoSegment if regions move upper
+  // and current __PRELINKED_INFO gets shifted.
+  //
+  CopyMem (
+    (VOID *) Command.Address,
+    Context->PrelinkedInfoSegment,
+    Context->PrelinkedInfoSegment->CommandSize
+    );
+
+  //
+  // Must choose a different name to avoid collisions.
+  //
+  CopyMem (Context->PrelinkedInfoSegment->SegmentName, "__KREMLIN_START", sizeof ("__KREMLIN_START"));
+  CopyMem (Context->PrelinkedInfoSection->SectionName, "__kremlin_start", sizeof ("__kremlin_start"));
+
+  //
+  // Refresh Mach-O header constants to include the new segment command.
+  //
+  MachHeader->NumCommands++;
+  MachHeader->CommandsSize += Context->PrelinkedInfoSegment->CommandSize;
+
+  //
+  // Update __PRELINKED_INFO pointers to get them updated at a later stage.
+  //
+  Context->PrelinkedInfoSegment = (MACH_SEGMENT_COMMAND_64 *) Command.Address;
+  Context->PrelinkedInfoSection = &Context->PrelinkedInfoSegment->Sections[0];
 }
 
 EFI_STATUS
@@ -163,7 +201,7 @@ KcRebuildMachHeader (
 
   CurrentSize  = MachHeader->CommandsSize + sizeof (*MachHeader);
   FilesetSize  = InternalKcGetKextFilesetSize (Context);
-  RequiredSize = FilesetSize + sizeof (MACH_LOAD_COMMAND_SEGMENT_64);
+  RequiredSize = FilesetSize + sizeof (MACH_LOAD_COMMAND_SEGMENT_64) + Context->PrelinkedInfoSegment->CommandSize;
 
   TextSegment = MachoGetSegmentByName64 (
     &Context->PrelinkedMachContext,

diff --git a/Library/OcAppleKernelLib/PrelinkedContext.c b/Library/OcAppleKernelLib/PrelinkedContext.c
@@ -652,12 +652,35 @@ PrelinkedInjectComplete (
     return EFI_BUFFER_TOO_SMALL;
   }
 
+#if 0
+  //
+  // This is a potential optimisation for smaller kexts allowing us to use less space.
+  // This requires disable __KREMLIN relocation segment addition.
+  //
+  if (Context->IsKernelCollection && MACHO_ALIGN (ExportedInfoSize) <= Context->PrelinkedInfoSegment->Size) {
+    CopyMem (
+      &Context->Prelinked[Context->PrelinkedInfoSegment->FileOffset],
+      ExportedInfo,
+      ExportedInfoSize
+      );
+
+    ZeroMem (
+      &Context->Prelinked[Context->PrelinkedInfoSegment->FileOffset + ExportedInfoSize],
+      Context->PrelinkedInfoSegment->FileSize - ExportedInfoSize
+      );
+
+    FreePool (ExportedInfo);
+
+    return EFI_SUCCESS;
+  }
+#endif
+
   Context->PrelinkedInfoSegment->VirtualAddress = Context->PrelinkedLastAddress;
-  Context->PrelinkedInfoSegment->Size           = ExportedInfoSize;
+  Context->PrelinkedInfoSegment->Size           = MACHO_ALIGN (ExportedInfoSize);
   Context->PrelinkedInfoSegment->FileOffset     = Context->PrelinkedSize;
-  Context->PrelinkedInfoSegment->FileSize       = ExportedInfoSize;
+  Context->PrelinkedInfoSegment->FileSize       = MACHO_ALIGN (ExportedInfoSize);
   Context->PrelinkedInfoSection->Address        = Context->PrelinkedLastAddress;
-  Context->PrelinkedInfoSection->Size           = ExportedInfoSize;
+  Context->PrelinkedInfoSection->Size           = MACHO_ALIGN (ExportedInfoSize);
   Context->PrelinkedInfoSection->Offset         = Context->PrelinkedSize;
 
   if (Context->IsKernelCollection) {
@@ -666,11 +689,11 @@ PrelinkedInjectComplete (
     // in both inner and outer images.
     //
     Context->InnerInfoSegment->VirtualAddress = Context->PrelinkedLastAddress;
-    Context->InnerInfoSegment->Size           = ExportedInfoSize;
+    Context->InnerInfoSegment->Size           = MACHO_ALIGN (ExportedInfoSize);
     Context->InnerInfoSegment->FileOffset     = Context->PrelinkedSize;
-    Context->InnerInfoSegment->FileSize       = ExportedInfoSize;
+    Context->InnerInfoSegment->FileSize       = MACHO_ALIGN (ExportedInfoSize);
     Context->InnerInfoSection->Address        = Context->PrelinkedLastAddress;
-    Context->InnerInfoSection->Size           = ExportedInfoSize;
+    Context->InnerInfoSection->Size           = MACHO_ALIGN (ExportedInfoSize);
     Context->InnerInfoSection->Offset         = Context->PrelinkedSize;
   }