[Lldb-commits] [lldb] [lldb] Fix nullptr dereference on running x86 binary with x86-disabled llvm (PR #82603)

[Daniil Kovalev via lldb-commits]

https://github.com/kovdan01 created https://github.com/llvm/llvm-project/pull/82603

If `LLVM_TARGETS_TO_BUILD` does not contain `X86` and we try to run an x86 binary in lldb, we get a `nullptr` dereference in `LLVMDisasmInstruction(...)`. We try to call `getDisAsm()` method on a `LLVMDisasmContext *DC` which is null. The pointer is passed from `x86AssemblyInspectionEngine::instruction_length(...)` and is originally `m_disasm_context` member of `x86AssemblyInspectionEngine`. This should be filled by `LLVMCreateDisasm(...)` in the class constructor, but not having X86 target enabled in llvm makes `TargetRegistry::lookupTarget(...)` call return `nullptr`, which results in `m_disasm_context` initialized with `nullptr` as well.

This patch adds if statements against `m_disasm_context` in `x86AssemblyInspectionEngine::GetNonCallSiteUnwindPlanFromAssembly(...)` and `x86AssemblyInspectionEngine::FindFirstNonPrologueInstruction(...)` so subsequent calls to `x86AssemblyInspectionEngine::instruction_length(...)` do not cause a null pointer dereference.

>From 5c9ac5382958d88cbe2b89128957b3a0908c9d88 Mon Sep 17 00:00:00 2001
From: Daniil Kovalev <dkovalev at accesssoftek.com>
Date: Thu, 22 Feb 2024 11:42:44 +0300
Subject: [PATCH] [lldb] Fix nullptr dereference on running x86 binary with
 x86-disabled llvm

If `LLVM_TARGETS_TO_BUILD` does not contain `X86` and we try to run an
x86 binary in lldb, we get a `nullptr` dereference in
`LLVMDisasmInstruction(...)`. We try to call `getDisAsm()` method on a
`LLVMDisasmContext *DC` which is null. The pointer is passed from
`x86AssemblyInspectionEngine::instruction_length(...)` and is originally
`m_disasm_context` member of `x86AssemblyInspectionEngine`. This should
be filled by `LLVMCreateDisasm(...)` in the class constructor, but not having
X86 target enabled in llvm makes `TargetRegistry::lookupTarget(...)`
call return `nullptr`, which results in `m_disasm_context` initialized
with `nullptr` as well.

This patch adds if statements against `m_disasm_context` in
`x86AssemblyInspectionEngine::GetNonCallSiteUnwindPlanFromAssembly(...)` and
`x86AssemblyInspectionEngine::FindFirstNonPrologueInstruction(...)` so
subsequent calls to `x86AssemblyInspectionEngine::instruction_length(...)` do
not cause a null pointer dereference.
---
 .../UnwindAssembly/x86/x86AssemblyInspectionEngine.cpp      | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/lldb/source/Plugins/UnwindAssembly/x86/x86AssemblyInspectionEngine.cpp b/lldb/source/Plugins/UnwindAssembly/x86/x86AssemblyInspectionEngine.cpp
index 2032c5a68d054c..6bfaa54135a959 100644
--- a/lldb/source/Plugins/UnwindAssembly/x86/x86AssemblyInspectionEngine.cpp
+++ b/lldb/source/Plugins/UnwindAssembly/x86/x86AssemblyInspectionEngine.cpp
@@ -909,6 +909,9 @@ bool x86AssemblyInspectionEngine::GetNonCallSiteUnwindPlanFromAssembly(
   if (!m_register_map_initialized)
     return false;
 
+  if (m_disasm_context == nullptr)
+    return false;
+
   addr_t current_func_text_offset = 0;
   int current_sp_bytes_offset_from_fa = 0;
   bool is_aligned = false;
@@ -1570,6 +1573,9 @@ bool x86AssemblyInspectionEngine::FindFirstNonPrologueInstruction(
   if (!m_register_map_initialized)
     return false;
 
+  if (m_disasm_context == nullptr)
+    return false;
+
   while (offset < size) {
     int regno;
     int insn_len;