[Lldb-commits] [PATCH] D147462: Use kernel's global variable indicating how many bits are used in addressing when loading Darwin xnu kernel

[Jason Molenda via Phabricator via lldb-commits]

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The Darwin xnu kernel has a global variable which has the number of bits used for addressing in ptrauth code.  The DynamicLoaderDarwinKernel already knows to look at xnu global variables to load kexts (solibs for a kernel); it's a natural place to find & use this information to set the number of bits correctly for the Process.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D147462

Files:
  lldb/source/Plugins/DynamicLoader/Darwin-Kernel/DynamicLoaderDarwinKernel.cpp


Index: lldb/source/Plugins/DynamicLoader/Darwin-Kernel/DynamicLoaderDarwinKernel.cpp
===================================================================
--- lldb/source/Plugins/DynamicLoader/Darwin-Kernel/DynamicLoaderDarwinKernel.cpp
+++ lldb/source/Plugins/DynamicLoader/Darwin-Kernel/DynamicLoaderDarwinKernel.cpp
@@ -1068,6 +1068,7 @@
 
     if (m_kernel.IsLoaded() && m_kernel.GetModule()) {
       static ConstString kext_summary_symbol("gLoadedKextSummaries");
+      static ConstString arm64_T1Sz_value("gT1Sz");
       const Symbol *symbol =
           m_kernel.GetModule()->FindFirstSymbolWithNameAndType(
               kext_summary_symbol, eSymbolTypeData);
@@ -1076,6 +1077,45 @@
         // Update all image infos
         ReadAllKextSummaries();
       }
+      // If the kernel global with the T1Sz setting is available,
+      // update the target.process.virtual-addressable-bits to be correct.
+      symbol = m_kernel.GetModule()->FindFirstSymbolWithNameAndType(
+          arm64_T1Sz_value, eSymbolTypeData);
+      uint32_t wordsize =
+          m_process->GetTarget().GetArchitecture().GetAddressByteSize();
+      if (symbol && wordsize == 8) {
+        if (symbol->GetByteSizeIsValid()) {
+          // Mark all bits as addressable so we don't strip any from our
+          // memory read below, with an incorrect default value.
+          uint32_t old_bits_value = m_process->GetVirtualAddressableBits();
+          // b55 is the sign extension bit with PAC, b56:63 are TBI,
+          // don't mark those as addressable.
+          m_process->SetVirtualAddressableBits((wordsize * 8) - 9);
+          addr_t sym_addr = symbol->GetLoadAddress(&m_process->GetTarget());
+          Status error;
+          // The definition of gT1Sz is in the xnu sources -- it is 8 bytes.
+          // We may be running on a stripped kernel binary and the size of
+          // the Symbol may be incorrect because neighboring symbols have
+          // been stripped out.  Hardcode it to 8 bytes here to sidestep
+          // this problem.
+          const size_t bytesize = 8; // size of gT1Sz value
+          uint64_t sym_value =
+              m_process->GetTarget().ReadUnsignedIntegerFromMemory(
+                  sym_addr, bytesize, 0, error, /*force_live_memory=*/true);
+          if (error.Success()) {
+            // 64 - T1Sz is the highest bit used for auth.
+            // The value we pass in to SetVirtualAddressableBits is
+            // the number of bits used for addressing, so if
+            // T1Sz is 25, then 64-25 == 39, bits 0..38 are used for
+            // addressing, bits 39..63 are used for PAC/TBI or whatever.
+            int virt_addr_bits = 64 - sym_value;
+            m_process->SetVirtualAddressableBits(virt_addr_bits);
+          } else {
+            if (old_bits_value != 0)
+              m_process->SetVirtualAddressableBits(old_bits_value);
+          }
+        }
+      }
     } else {
       m_kernel.Clear();
     }


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