diff --git a/src/_pytest/config/__init__.py b/src/_pytest/config/__init__.py
index 3107950f6..f499a349a 100644
--- a/src/_pytest/config/__init__.py
+++ b/src/_pytest/config/__init__.py
@@ -42,6 +42,7 @@ from _pytest.compat import TYPE_CHECKING
 from _pytest.outcomes import fail
 from _pytest.outcomes import Skipped
 from _pytest.pathlib import Path
+from _pytest.store import Store
 from _pytest.warning_types import PytestConfigWarning
 
 if TYPE_CHECKING:
@@ -791,6 +792,9 @@ class Config:
         self._override_ini = ()  # type: Sequence[str]
         self._opt2dest = {}  # type: Dict[str, str]
         self._cleanup = []  # type: List[Callable[[], None]]
+        # A place where plugins can store information on the config for their
+        # own use. Currently only intended for internal plugins.
+        self._store = Store()
         self.pluginmanager.register(self, "pytestconfig")
         self._configured = False
         self.hook.pytest_addoption.call_historic(
diff --git a/src/_pytest/faulthandler.py b/src/_pytest/faulthandler.py
index ed2dfd025..8d723c206 100644
--- a/src/_pytest/faulthandler.py
+++ b/src/_pytest/faulthandler.py
@@ -1,8 +1,13 @@
 import io
 import os
 import sys
+from typing import TextIO
 
 import pytest
+from _pytest.store import StoreKey
+
+
+fault_handler_stderr_key = StoreKey[TextIO]()
 
 
 def pytest_addoption(parser):
@@ -46,8 +51,8 @@ class FaultHandlerHooks:
         import faulthandler
 
         stderr_fd_copy = os.dup(self._get_stderr_fileno())
-        config.fault_handler_stderr = os.fdopen(stderr_fd_copy, "w")
-        faulthandler.enable(file=config.fault_handler_stderr)
+        config._store[fault_handler_stderr_key] = open(stderr_fd_copy, "w")
+        faulthandler.enable(file=config._store[fault_handler_stderr_key])
 
     def pytest_unconfigure(self, config):
         import faulthandler
@@ -57,8 +62,8 @@ class FaultHandlerHooks:
         # re-enable the faulthandler, attaching it to the default sys.stderr
         # so we can see crashes after pytest has finished, usually during
         # garbage collection during interpreter shutdown
-        config.fault_handler_stderr.close()
-        del config.fault_handler_stderr
+        config._store[fault_handler_stderr_key].close()
+        del config._store[fault_handler_stderr_key]
         faulthandler.enable(file=self._get_stderr_fileno())
 
     @staticmethod
@@ -78,7 +83,7 @@ class FaultHandlerHooks:
     @pytest.hookimpl(hookwrapper=True)
     def pytest_runtest_protocol(self, item):
         timeout = self.get_timeout_config_value(item.config)
-        stderr = item.config.fault_handler_stderr
+        stderr = item.config._store[fault_handler_stderr_key]
         if timeout > 0 and stderr is not None:
             import faulthandler
 
diff --git a/src/_pytest/junitxml.py b/src/_pytest/junitxml.py
index 6ef535839..77e184312 100644
--- a/src/_pytest/junitxml.py
+++ b/src/_pytest/junitxml.py
@@ -22,9 +22,13 @@ import pytest
 from _pytest import deprecated
 from _pytest import nodes
 from _pytest.config import filename_arg
+from _pytest.store import StoreKey
 from _pytest.warnings import _issue_warning_captured
 
 
+xml_key = StoreKey["LogXML"]()
+
+
 class Junit(py.xml.Namespace):
     pass
 
@@ -260,7 +264,7 @@ def _warn_incompatibility_with_xunit2(request, fixture_name):
     """Emits a PytestWarning about the given fixture being incompatible with newer xunit revisions"""
     from _pytest.warning_types import PytestWarning
 
-    xml = getattr(request.config, "_xml", None)
+    xml = request.config._store.get(xml_key, None)
     if xml is not None and xml.family not in ("xunit1", "legacy"):
         request.node.warn(
             PytestWarning(
@@ -312,7 +316,7 @@ def record_xml_attribute(request):
 
     attr_func = add_attr_noop
 
-    xml = getattr(request.config, "_xml", None)
+    xml = request.config._store.get(xml_key, None)
     if xml is not None:
         node_reporter = xml.node_reporter(request.node.nodeid)
         attr_func = node_reporter.add_attribute
@@ -353,7 +357,7 @@ def record_testsuite_property(request):
         __tracebackhide__ = True
         _check_record_param_type("name", name)
 
-    xml = getattr(request.config, "_xml", None)
+    xml = request.config._store.get(xml_key, None)
     if xml is not None:
         record_func = xml.add_global_property  # noqa
     return record_func
@@ -412,7 +416,7 @@ def pytest_configure(config):
         if not junit_family:
             _issue_warning_captured(deprecated.JUNIT_XML_DEFAULT_FAMILY, config.hook, 2)
             junit_family = "xunit1"
-        config._xml = LogXML(
+        config._store[xml_key] = LogXML(
             xmlpath,
             config.option.junitprefix,
             config.getini("junit_suite_name"),
@@ -421,13 +425,13 @@ def pytest_configure(config):
             junit_family,
             config.getini("junit_log_passing_tests"),
         )
-        config.pluginmanager.register(config._xml)
+        config.pluginmanager.register(config._store[xml_key])
 
 
 def pytest_unconfigure(config):
-    xml = getattr(config, "_xml", None)
+    xml = config._store.get(xml_key, None)
     if xml:
-        del config._xml
+        del config._store[xml_key]
         config.pluginmanager.unregister(xml)
 
 
diff --git a/src/_pytest/mark/__init__.py b/src/_pytest/mark/__init__.py
index f493bd839..dab0cf149 100644
--- a/src/_pytest/mark/__init__.py
+++ b/src/_pytest/mark/__init__.py
@@ -1,4 +1,6 @@
 """ generic mechanism for marking and selecting python functions. """
+from typing import Optional
+
 from .legacy import matchkeyword
 from .legacy import matchmark
 from .structures import EMPTY_PARAMETERSET_OPTION
@@ -8,12 +10,17 @@ from .structures import MARK_GEN
 from .structures import MarkDecorator
 from .structures import MarkGenerator
 from .structures import ParameterSet
+from _pytest.config import Config
 from _pytest.config import hookimpl
 from _pytest.config import UsageError
+from _pytest.store import StoreKey
 
 __all__ = ["Mark", "MarkDecorator", "MarkGenerator", "get_empty_parameterset_mark"]
 
 
+old_mark_config_key = StoreKey[Optional[Config]]()
+
+
 def param(*values, **kw):
     """Specify a parameter in `pytest.mark.parametrize`_ calls or
     :ref:`parametrized fixtures <fixture-parametrize-marks>`.
@@ -145,7 +152,7 @@ def pytest_collection_modifyitems(items, config):
 
 
 def pytest_configure(config):
-    config._old_mark_config = MARK_GEN._config
+    config._store[old_mark_config_key] = MARK_GEN._config
     MARK_GEN._config = config
 
     empty_parameterset = config.getini(EMPTY_PARAMETERSET_OPTION)
@@ -158,4 +165,4 @@ def pytest_configure(config):
 
 
 def pytest_unconfigure(config):
-    MARK_GEN._config = getattr(config, "_old_mark_config", None)
+    MARK_GEN._config = config._store.get(old_mark_config_key, None)
diff --git a/src/_pytest/nodes.py b/src/_pytest/nodes.py
index dbf93356f..45f0aa8a1 100644
--- a/src/_pytest/nodes.py
+++ b/src/_pytest/nodes.py
@@ -29,6 +29,7 @@ from _pytest.mark.structures import MarkDecorator
 from _pytest.mark.structures import NodeKeywords
 from _pytest.outcomes import fail
 from _pytest.outcomes import Failed
+from _pytest.store import Store
 
 if TYPE_CHECKING:
     # Imported here due to circular import.
@@ -146,6 +147,10 @@ class Node(metaclass=NodeMeta):
             if self.name != "()":
                 self._nodeid += "::" + self.name
 
+        # A place where plugins can store information on the node for their
+        # own use. Currently only intended for internal plugins.
+        self._store = Store()
+
     @classmethod
     def from_parent(cls, parent: "Node", **kw):
         """
diff --git a/src/_pytest/pastebin.py b/src/_pytest/pastebin.py
index 77b4e2621..3f4a7502d 100644
--- a/src/_pytest/pastebin.py
+++ b/src/_pytest/pastebin.py
@@ -1,7 +1,12 @@
 """ submit failure or test session information to a pastebin service. """
 import tempfile
+from typing import IO
 
 import pytest
+from _pytest.store import StoreKey
+
+
+pastebinfile_key = StoreKey[IO[bytes]]()
 
 
 def pytest_addoption(parser):
@@ -26,25 +31,26 @@ def pytest_configure(config):
         # when using pytest-xdist, for example
         if tr is not None:
             # pastebin file will be utf-8 encoded binary file
-            config._pastebinfile = tempfile.TemporaryFile("w+b")
+            config._store[pastebinfile_key] = tempfile.TemporaryFile("w+b")
             oldwrite = tr._tw.write
 
             def tee_write(s, **kwargs):
                 oldwrite(s, **kwargs)
                 if isinstance(s, str):
                     s = s.encode("utf-8")
-                config._pastebinfile.write(s)
+                config._store[pastebinfile_key].write(s)
 
             tr._tw.write = tee_write
 
 
 def pytest_unconfigure(config):
-    if hasattr(config, "_pastebinfile"):
+    if pastebinfile_key in config._store:
+        pastebinfile = config._store[pastebinfile_key]
         # get terminal contents and delete file
-        config._pastebinfile.seek(0)
-        sessionlog = config._pastebinfile.read()
-        config._pastebinfile.close()
-        del config._pastebinfile
+        pastebinfile.seek(0)
+        sessionlog = pastebinfile.read()
+        pastebinfile.close()
+        del config._store[pastebinfile_key]
         # undo our patching in the terminal reporter
         tr = config.pluginmanager.getplugin("terminalreporter")
         del tr._tw.__dict__["write"]
diff --git a/src/_pytest/resultlog.py b/src/_pytest/resultlog.py
index a977b29da..6269c16f2 100644
--- a/src/_pytest/resultlog.py
+++ b/src/_pytest/resultlog.py
@@ -5,6 +5,11 @@ import os
 
 import py
 
+from _pytest.store import StoreKey
+
+
+resultlog_key = StoreKey["ResultLog"]()
+
 
 def pytest_addoption(parser):
     group = parser.getgroup("terminal reporting", "resultlog plugin options")
@@ -26,8 +31,8 @@ def pytest_configure(config):
         if not os.path.isdir(dirname):
             os.makedirs(dirname)
         logfile = open(resultlog, "w", 1)  # line buffered
-        config._resultlog = ResultLog(config, logfile)
-        config.pluginmanager.register(config._resultlog)
+        config._store[resultlog_key] = ResultLog(config, logfile)
+        config.pluginmanager.register(config._store[resultlog_key])
 
         from _pytest.deprecated import RESULT_LOG
         from _pytest.warnings import _issue_warning_captured
@@ -36,10 +41,10 @@ def pytest_configure(config):
 
 
 def pytest_unconfigure(config):
-    resultlog = getattr(config, "_resultlog", None)
+    resultlog = config._store.get(resultlog_key, None)
     if resultlog:
         resultlog.logfile.close()
-        del config._resultlog
+        del config._store[resultlog_key]
         config.pluginmanager.unregister(resultlog)
 
 
diff --git a/src/_pytest/skipping.py b/src/_pytest/skipping.py
index f70ef7f59..fe8742c66 100644
--- a/src/_pytest/skipping.py
+++ b/src/_pytest/skipping.py
@@ -4,6 +4,12 @@ from _pytest.mark.evaluate import MarkEvaluator
 from _pytest.outcomes import fail
 from _pytest.outcomes import skip
 from _pytest.outcomes import xfail
+from _pytest.store import StoreKey
+
+
+skipped_by_mark_key = StoreKey[bool]()
+evalxfail_key = StoreKey[MarkEvaluator]()
+unexpectedsuccess_key = StoreKey[str]()
 
 
 def pytest_addoption(parser):
@@ -68,14 +74,14 @@ def pytest_configure(config):
 @hookimpl(tryfirst=True)
 def pytest_runtest_setup(item):
     # Check if skip or skipif are specified as pytest marks
-    item._skipped_by_mark = False
+    item._store[skipped_by_mark_key] = False
     eval_skipif = MarkEvaluator(item, "skipif")
     if eval_skipif.istrue():
-        item._skipped_by_mark = True
+        item._store[skipped_by_mark_key] = True
         skip(eval_skipif.getexplanation())
 
     for skip_info in item.iter_markers(name="skip"):
-        item._skipped_by_mark = True
+        item._store[skipped_by_mark_key] = True
         if "reason" in skip_info.kwargs:
             skip(skip_info.kwargs["reason"])
         elif skip_info.args:
@@ -83,7 +89,7 @@ def pytest_runtest_setup(item):
         else:
             skip("unconditional skip")
 
-    item._evalxfail = MarkEvaluator(item, "xfail")
+    item._store[evalxfail_key] = MarkEvaluator(item, "xfail")
     check_xfail_no_run(item)
 
 
@@ -99,7 +105,7 @@ def pytest_pyfunc_call(pyfuncitem):
 def check_xfail_no_run(item):
     """check xfail(run=False)"""
     if not item.config.option.runxfail:
-        evalxfail = item._evalxfail
+        evalxfail = item._store[evalxfail_key]
         if evalxfail.istrue():
             if not evalxfail.get("run", True):
                 xfail("[NOTRUN] " + evalxfail.getexplanation())
@@ -107,12 +113,12 @@ def check_xfail_no_run(item):
 
 def check_strict_xfail(pyfuncitem):
     """check xfail(strict=True) for the given PASSING test"""
-    evalxfail = pyfuncitem._evalxfail
+    evalxfail = pyfuncitem._store[evalxfail_key]
     if evalxfail.istrue():
         strict_default = pyfuncitem.config.getini("xfail_strict")
         is_strict_xfail = evalxfail.get("strict", strict_default)
         if is_strict_xfail:
-            del pyfuncitem._evalxfail
+            del pyfuncitem._store[evalxfail_key]
             explanation = evalxfail.getexplanation()
             fail("[XPASS(strict)] " + explanation, pytrace=False)
 
@@ -121,12 +127,12 @@ def check_strict_xfail(pyfuncitem):
 def pytest_runtest_makereport(item, call):
     outcome = yield
     rep = outcome.get_result()
-    evalxfail = getattr(item, "_evalxfail", None)
-    # unittest special case, see setting of _unexpectedsuccess
-    if hasattr(item, "_unexpectedsuccess") and rep.when == "call":
-
-        if item._unexpectedsuccess:
-            rep.longrepr = "Unexpected success: {}".format(item._unexpectedsuccess)
+    evalxfail = item._store.get(evalxfail_key, None)
+    # unittest special case, see setting of unexpectedsuccess_key
+    if unexpectedsuccess_key in item._store and rep.when == "call":
+        reason = item._store[unexpectedsuccess_key]
+        if reason:
+            rep.longrepr = "Unexpected success: {}".format(reason)
         else:
             rep.longrepr = "Unexpected success"
         rep.outcome = "failed"
@@ -154,7 +160,7 @@ def pytest_runtest_makereport(item, call):
                 rep.outcome = "passed"
                 rep.wasxfail = explanation
     elif (
-        getattr(item, "_skipped_by_mark", False)
+        item._store.get(skipped_by_mark_key, True)
         and rep.skipped
         and type(rep.longrepr) is tuple
     ):
diff --git a/src/_pytest/store.py b/src/_pytest/store.py
new file mode 100644
index 000000000..0dcea1b93
--- /dev/null
+++ b/src/_pytest/store.py
@@ -0,0 +1,116 @@
+from typing import Any
+from typing import cast
+from typing import Dict
+from typing import Generic
+from typing import TypeVar
+from typing import Union
+
+
+__all__ = ["Store", "StoreKey"]
+
+
+T = TypeVar("T")
+D = TypeVar("D")
+
+
+class StoreKey(Generic[T]):
+    """StoreKey is an object used as a key to a Store.
+
+    A StoreKey is associated with the type T of the value of the key.
+
+    A StoreKey is unique and cannot conflict with another key.
+    """
+
+    __slots__ = ()
+
+
+class Store:
+    """Store is a type-safe heterogenous mutable mapping that
+    allows keys and value types to be defined separately from
+    where it is defined.
+
+    Usually you will be given an object which has a ``Store``:
+
+    .. code-block:: python
+
+        store: Store = some_object.store
+
+    If a module wants to store data in this Store, it creates StoreKeys
+    for its keys (at the module level):
+
+    .. code-block:: python
+
+        some_str_key = StoreKey[str]()
+        some_bool_key = StoreKey[bool]()
+
+    To store information:
+
+    .. code-block:: python
+
+        # Value type must match the key.
+        store[some_str_key] = "value"
+        store[some_bool_key] = True
+
+    To retrieve the information:
+
+    .. code-block:: python
+
+        # The static type of some_str is str.
+        some_str = store[some_str_key]
+        # The static type of some_bool is bool.
+        some_bool = store[some_bool_key]
+
+    Why use this?
+    -------------
+
+    Problem: module Internal defines an object. Module External, which
+    module Internal doesn't know about, receives the object and wants to
+    attach information to it, to be retrieved later given the object.
+
+    Bad solution 1: Module External assigns private attributes directly on
+    the object. This doesn't work well because the type checker doesn't
+    know about these attributes and it complains about undefined attributes.
+
+    Bad solution 2: module Internal adds a ``Dict[str, Any]`` attribute to
+    the object. Module External stores its data in private keys of this dict.
+    This doesn't work well because retrieved values are untyped.
+
+    Good solution: module Internal adds a ``Store`` to the object. Module
+    External mints StoreKeys for its own keys. Module External stores and
+    retrieves its data using its keys.
+    """
+
+    __slots__ = ("_store",)
+
+    def __init__(self) -> None:
+        self._store = {}  # type: Dict[StoreKey[Any], object]
+
+    def __setitem__(self, key: StoreKey[T], value: T) -> None:
+        """Set a value for key."""
+        self._store[key] = value
+
+    def __getitem__(self, key: StoreKey[T]) -> T:
+        """Get the value for key.
+
+        Raises KeyError if the key wasn't set before.
+        """
+        return cast(T, self._store[key])
+
+    def get(self, key: StoreKey[T], default: D) -> Union[T, D]:
+        """Get the value for key, or return default if the key wasn't set
+        before."""
+        try:
+            return self[key]
+        except KeyError:
+            return default
+
+    def __delitem__(self, key: StoreKey[T]) -> None:
+        """Delete the value for key.
+
+        Raises KeyError if the key wasn't set before.
+        """
+        del self._store[key]
+
+    def __contains__(self, key: StoreKey[T]) -> bool:
+        """Returns whether key was set."""
+        return key in self._store
diff --git a/src/_pytest/unittest.py b/src/_pytest/unittest.py
index a5512e944..2047876e5 100644
--- a/src/_pytest/unittest.py
+++ b/src/_pytest/unittest.py
@@ -14,6 +14,8 @@ from _pytest.outcomes import xfail
 from _pytest.python import Class
 from _pytest.python import Function
 from _pytest.runner import CallInfo
+from _pytest.skipping import skipped_by_mark_key
+from _pytest.skipping import unexpectedsuccess_key
 
 
 def pytest_pycollect_makeitem(collector, name, obj):
@@ -174,7 +176,7 @@ class TestCaseFunction(Function):
         try:
             skip(reason)
         except skip.Exception:
-            self._skipped_by_mark = True
+            self._store[skipped_by_mark_key] = True
             self._addexcinfo(sys.exc_info())
 
     def addExpectedFailure(self, testcase, rawexcinfo, reason=""):
@@ -184,7 +186,7 @@ class TestCaseFunction(Function):
             self._addexcinfo(sys.exc_info())
 
     def addUnexpectedSuccess(self, testcase, reason=""):
-        self._unexpectedsuccess = reason
+        self._store[unexpectedsuccess_key] = reason
 
     def addSuccess(self, testcase):
         pass
diff --git a/testing/test_junitxml.py b/testing/test_junitxml.py
index ef2f808a2..0d6adb3a0 100644
--- a/testing/test_junitxml.py
+++ b/testing/test_junitxml.py
@@ -10,6 +10,7 @@ import pytest
 from _pytest.junitxml import LogXML
 from _pytest.pathlib import Path
 from _pytest.reports import BaseReport
+from _pytest.store import Store
 
 
 @pytest.fixture(scope="session")
@@ -865,6 +866,7 @@ def test_dont_configure_on_slaves(tmpdir):
         def __init__(self):
             self.pluginmanager = self
             self.option = self
+            self._store = Store()
 
         def getini(self, name):
             return "pytest"
diff --git a/testing/test_resultlog.py b/testing/test_resultlog.py
index b6f957b40..e0a02de80 100644
--- a/testing/test_resultlog.py
+++ b/testing/test_resultlog.py
@@ -6,6 +6,7 @@ import pytest
 from _pytest.resultlog import pytest_configure
 from _pytest.resultlog import pytest_unconfigure
 from _pytest.resultlog import ResultLog
+from _pytest.resultlog import resultlog_key
 
 pytestmark = pytest.mark.filterwarnings("ignore:--result-log is deprecated")
 
@@ -179,17 +180,17 @@ def test_makedir_for_resultlog(testdir, LineMatcher):
 def test_no_resultlog_on_slaves(testdir):
     config = testdir.parseconfig("-p", "resultlog", "--resultlog=resultlog")
 
-    assert not hasattr(config, "_resultlog")
+    assert resultlog_key not in config._store
     pytest_configure(config)
-    assert hasattr(config, "_resultlog")
+    assert resultlog_key in config._store
     pytest_unconfigure(config)
-    assert not hasattr(config, "_resultlog")
+    assert resultlog_key not in config._store
 
     config.slaveinput = {}
     pytest_configure(config)
-    assert not hasattr(config, "_resultlog")
+    assert resultlog_key not in config._store
     pytest_unconfigure(config)
-    assert not hasattr(config, "_resultlog")
+    assert resultlog_key not in config._store
 
 
 def test_failure_issue380(testdir):
diff --git a/testing/test_store.py b/testing/test_store.py
new file mode 100644
index 000000000..ae6cfccdd
--- /dev/null
+++ b/testing/test_store.py
@@ -0,0 +1,52 @@
+import pytest
+from _pytest.store import Store
+from _pytest.store import StoreKey
+
+
+def test_store() -> None:
+    store = Store()
+
+    key1 = StoreKey[str]()
+    key2 = StoreKey[int]()
+
+    # Basic functionality - single key.
+    assert key1 not in store
+    store[key1] = "hello"
+    assert key1 in store
+    assert store[key1] == "hello"
+    assert store.get(key1, None) == "hello"
+    store[key1] = "world"
+    assert store[key1] == "world"
+    # Has correct type (no mypy error).
+    store[key1] + "string"
+
+    # No interaction with another key.
+    assert key2 not in store
+    assert store.get(key2, None) is None
+    with pytest.raises(KeyError):
+        store[key2]
+    with pytest.raises(KeyError):
+        del store[key2]
+    store[key2] = 1
+    assert store[key2] == 1
+    # Has correct type (no mypy error).
+    store[key2] + 20
+    del store[key1]
+    with pytest.raises(KeyError):
+        del store[key1]
+    with pytest.raises(KeyError):
+        store[key1]
+
+    # Can't accidentally add attributes to store object itself.
+    with pytest.raises(AttributeError):
+        store.foo = "nope"  # type: ignore[attr-defined] # noqa: F821
+
+    # No interaction with anoter store.
+    store2 = Store()
+    key3 = StoreKey[int]()
+    assert key2 not in store2
+    store2[key2] = 100
+    store2[key3] = 200
+    assert store2[key2] + store2[key3] == 300
+    assert store[key2] == 1
+    assert key3 not in store