From a0b29678c87a6a37c7e8a0df76788c71a3fbe7af Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?B=C3=A9n=C3=A9dikt=20Tran?=
 <10796600+picnixz@users.noreply.github.com>
Date: Mon, 12 May 2025 17:57:24 +0200
Subject: [PATCH 1/3] fix UBSan failures in `faulthandler.c`

- reading from NULL is no more an undefined behavior for C11
- instead of using 1/0 arithmetic, we explicitly raise SIGFPE
---
 Modules/faulthandler.c | 21 +++++----------------
 1 file changed, 5 insertions(+), 16 deletions(-)

diff --git a/Modules/faulthandler.c b/Modules/faulthandler.c
index d49ce794d88674..c52a0ff43788b0 100644
--- a/Modules/faulthandler.c
+++ b/Modules/faulthandler.c
@@ -1069,8 +1069,8 @@ faulthandler_suppress_crash_report(void)
 #endif
 }
 
-static PyObject* _Py_NO_SANITIZE_UNDEFINED
-faulthandler_read_null(PyObject *self, PyObject *args)
+static PyObject*
+faulthandler_read_null(PyObject *self, PyObject *Py_UNUSED(args))
 {
     volatile int *x;
     volatile int y;
@@ -1079,7 +1079,6 @@ faulthandler_read_null(PyObject *self, PyObject *args)
     x = NULL;
     y = *x;
     return PyLong_FromLong(y);
-
 }
 
 static void
@@ -1158,23 +1157,13 @@ faulthandler_fatal_error_c_thread(PyObject *self, PyObject *args)
     Py_RETURN_NONE;
 }
 
-static PyObject* _Py_NO_SANITIZE_UNDEFINED
+static PyObject*
 faulthandler_sigfpe(PyObject *self, PyObject *Py_UNUSED(dummy))
 {
     faulthandler_suppress_crash_report();
-
-    /* Do an integer division by zero: raise a SIGFPE on Intel CPU, but not on
-       PowerPC. Use volatile to disable compile-time optimizations. */
-    volatile int x = 1, y = 0, z;
-    z = x / y;
-
-    /* If the division by zero didn't raise a SIGFPE (e.g. on PowerPC),
-       raise it manually. */
+    /* raise SIGFPE manually to prevent crafted undefined behaviors */
     raise(SIGFPE);
-
-    /* This line is never reached, but we pretend to make something with z
-       to silence a compiler warning. */
-    return PyLong_FromLong(z);
+    Py_UNREACHABLE();
 }
 
 static PyObject *

From 130da649a195ea497b53df423d2a1a24329879e4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?B=C3=A9n=C3=A9dikt=20Tran?=
 <10796600+picnixz@users.noreply.github.com>
Date: Thu, 15 May 2025 17:30:04 +0200
Subject: [PATCH 2/3] Update Modules/faulthandler.c

---
 Modules/faulthandler.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/Modules/faulthandler.c b/Modules/faulthandler.c
index c52a0ff43788b0..b6c4c745a41602 100644
--- a/Modules/faulthandler.c
+++ b/Modules/faulthandler.c
@@ -1161,7 +1161,6 @@ static PyObject*
 faulthandler_sigfpe(PyObject *self, PyObject *Py_UNUSED(dummy))
 {
     faulthandler_suppress_crash_report();
-    /* raise SIGFPE manually to prevent crafted undefined behaviors */
     raise(SIGFPE);
     Py_UNREACHABLE();
 }

From 05d7ff1c1d791c5f77f235395121275750d9ebc9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?B=C3=A9n=C3=A9dikt=20Tran?=
 <10796600+picnixz@users.noreply.github.com>
Date: Fri, 16 May 2025 10:40:51 +0200
Subject: [PATCH 3/3] remove `faulthandler._read_null()`

Reading from NULL is an undefined behavior and `faulthandler`
should not check for low-level C about undefined behaviors.
---
 Lib/test/test_faulthandler.py | 23 -----------------------
 Modules/faulthandler.c        | 15 ---------------
 2 files changed, 38 deletions(-)

diff --git a/Lib/test/test_faulthandler.py b/Lib/test/test_faulthandler.py
index 371c63adce9412..2fb963f52e5138 100644
--- a/Lib/test/test_faulthandler.py
+++ b/Lib/test/test_faulthandler.py
@@ -166,29 +166,6 @@ def check_windows_exception(self, code, line_number, name_regex, **kw):
         fatal_error = 'Windows fatal exception: %s' % name_regex
         self.check_error(code, line_number, fatal_error, **kw)
 
-    @unittest.skipIf(sys.platform.startswith('aix'),
-                     "the first page of memory is a mapped read-only on AIX")
-    def test_read_null(self):
-        if not MS_WINDOWS:
-            self.check_fatal_error("""
-                import faulthandler
-                faulthandler.enable()
-                faulthandler._read_null()
-                """,
-                3,
-                # Issue #12700: Read NULL raises SIGILL on Mac OS X Lion
-                '(?:Segmentation fault'
-                    '|Bus error'
-                    '|Illegal instruction)')
-        else:
-            self.check_windows_exception("""
-                import faulthandler
-                faulthandler.enable()
-                faulthandler._read_null()
-                """,
-                3,
-                'access violation')
-
     @skip_segfault_on_android
     def test_sigsegv(self):
         self.check_fatal_error("""
diff --git a/Modules/faulthandler.c b/Modules/faulthandler.c
index b6c4c745a41602..c94f4f66366170 100644
--- a/Modules/faulthandler.c
+++ b/Modules/faulthandler.c
@@ -1069,17 +1069,6 @@ faulthandler_suppress_crash_report(void)
 #endif
 }
 
-static PyObject*
-faulthandler_read_null(PyObject *self, PyObject *Py_UNUSED(args))
-{
-    volatile int *x;
-    volatile int y;
-
-    faulthandler_suppress_crash_report();
-    x = NULL;
-    y = *x;
-    return PyLong_FromLong(y);
-}
 
 static void
 faulthandler_raise_sigsegv(void)
@@ -1304,10 +1293,6 @@ static PyMethodDef module_methods[] = {
                "Unregister the handler of the signal "
                "'signum' registered by register().")},
 #endif
-    {"_read_null", faulthandler_read_null, METH_NOARGS,
-     PyDoc_STR("_read_null($module, /)\n--\n\n"
-               "Read from NULL, raise "
-               "a SIGSEGV or SIGBUS signal depending on the platform.")},
     {"_sigsegv", faulthandler_sigsegv, METH_VARARGS,
      PyDoc_STR("_sigsegv($module, release_gil=False, /)\n--\n\n"
                "Raise a SIGSEGV signal.")},