[lldb] Handle an empty SBMemoryRegionInfo from scripted process (#115963)

A scripted process implementation might return an SBMemoryRegionInfo
object in its implementation of `get_memory_region_containing_address`
which will have an address 0 and size 0, without realizing the problems
this can cause. Several algorithms in lldb will try to iterate over the
MemoryRegions of the process, starting at address 0 and expecting to
iterate up to the highest vm address, stepping by the size of each
region, so a 0-length region will result in an infinite loop. Add a
check to Process::GetMemoryRegionInfo that rejects a MemoryRegion which
does not contain the requested address; a 0-length memory region will
therefor always be rejected.

rdar://139678032

lldb/source/Target/Process.cpp

@@ -6184,7 +6184,12 @@ Status Process::GetMemoryRegionInfo(lldb::addr_t load_addr,
                                     MemoryRegionInfo &range_info) {
   if (const lldb::ABISP &abi = GetABI())
     load_addr = abi->FixAnyAddress(load_addr);
-  return DoGetMemoryRegionInfo(load_addr, range_info);
+  Status error = DoGetMemoryRegionInfo(load_addr, range_info);
+  // Reject a region that does not contain the requested address.
+  if (error.Success() && !range_info.GetRange().Contains(load_addr))
+    error = Status::FromErrorString("Invalid memory region");
+
+  return error;
 }
 
 Status Process::GetMemoryRegions(lldb_private::MemoryRegionInfos &region_list) {

lldb/test/API/functionalities/scripted_process_empty_memory_region/Makefile

@@ -0,0 +1,3 @@
+C_SOURCES := main.c
+
+include Makefile.rules

lldb/test/API/functionalities/scripted_process_empty_memory_region/TestScriptedProcessEmptyMemoryRegion.py

@@ -0,0 +1,33 @@
+"""
+Test python scripted process which returns an empty SBMemoryRegionInfo
+"""
+
+import os, shutil
+
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+from lldbsuite.test import lldbtest
+
+
+class ScriptedProcessEmptyMemoryRegion(TestBase):
+    NO_DEBUG_INFO_TESTCASE = True
+
+    def test_scripted_process_empty_memory_region(self):
+        """Test that lldb handles an empty SBMemoryRegionInfo object from
+        a scripted process plugin."""
+        self.build()
+
+        target = self.dbg.CreateTarget(self.getBuildArtifact("a.out"))
+        self.assertTrue(target, VALID_TARGET)
+
+        scripted_process_example_relpath = "dummy_scripted_process.py"
+        self.runCmd(
+            "command script import "
+            + os.path.join(self.getSourceDir(), scripted_process_example_relpath)
+        )
+
+        self.expect("memory region 0", error=True, substrs=["Invalid memory region"])
+
+        self.expect("expr -- 5", substrs=["5"])

lldb/test/API/functionalities/scripted_process_empty_memory_region/dummy_scripted_process.py

@@ -0,0 +1,110 @@
+import os, struct, signal
+
+from typing import Any, Dict
+
+import lldb
+from lldb.plugins.scripted_process import ScriptedProcess
+from lldb.plugins.scripted_process import ScriptedThread
+
+
+class DummyScriptedProcess(ScriptedProcess):
+    memory = None
+
+    def __init__(self, exe_ctx: lldb.SBExecutionContext, args: lldb.SBStructuredData):
+        super().__init__(exe_ctx, args)
+        self.threads[0] = DummyScriptedThread(self, None)
+        self.memory = {}
+        addr = 0x500000000
+        debugger = self.target.GetDebugger()
+        index = debugger.GetIndexOfTarget(self.target)
+        self.memory[addr] = "Hello, target " + str(index)
+        self.handled_stop = False
+
+    def read_memory_at_address(
+        self, addr: int, size: int, error: lldb.SBError
+    ) -> lldb.SBData:
+        data = lldb.SBData().CreateDataFromCString(
+            self.target.GetByteOrder(), self.target.GetCodeByteSize(), self.memory[addr]
+        )
+
+        return data
+
+    def get_memory_region_containing_address(
+        self, addr: int
+    ) -> lldb.SBMemoryRegionInfo:
+        return lldb.SBMemoryRegionInfo()
+
+    def write_memory_at_address(self, addr, data, error):
+        self.memory[addr] = data.GetString(error, 0)
+        return len(self.memory[addr]) + 1
+
+    def get_loaded_images(self):
+        return self.loaded_images
+
+    def get_process_id(self) -> int:
+        return 42
+
+    def should_stop(self) -> bool:
+        return True
+
+    def is_alive(self) -> bool:
+        return True
+
+    def get_scripted_thread_plugin(self):
+        return DummyScriptedThread.__module__ + "." + DummyScriptedThread.__name__
+
+    def my_super_secret_method(self):
+        if hasattr(self, "my_super_secret_member"):
+            return self.my_super_secret_member
+        else:
+            return None
+
+
+class DummyScriptedThread(ScriptedThread):
+    def __init__(self, process, args):
+        super().__init__(process, args)
+        self.frames.append({"pc": 0x0100001B00})
+
+    def get_thread_id(self) -> int:
+        return 0x19
+
+    def get_name(self) -> str:
+        return DummyScriptedThread.__name__ + ".thread-1"
+
+    def get_state(self) -> int:
+        return lldb.eStateStopped
+
+    def get_stop_reason(self) -> Dict[str, Any]:
+        return {"type": lldb.eStopReasonTrace, "data": {}}
+
+    def get_register_context(self) -> str:
+        return struct.pack(
+            "21Q",
+            1,
+            2,
+            3,
+            4,
+            5,
+            6,
+            7,
+            8,
+            9,
+            10,
+            11,
+            12,
+            13,
+            14,
+            15,
+            16,
+            17,
+            18,
+            19,
+            20,
+            21,
+        )
+
+
+def __lldb_init_module(debugger, dict):
+    debugger.HandleCommand(
+        "process launch -C %s.%s" % (__name__, DummyScriptedProcess.__name__)
+    )

lldb/test/API/functionalities/scripted_process_empty_memory_region/main.c

@@ -0,0 +1 @@
+int main() {}