Fix GH-15657: Segmentation fault in ext/opcache/jit/ir/dynasm/dasm_x86.h

The crash happens because the zend_persist.c code tries to JIT the hook's
op_array while the JIT buffer memory is still protected. This happens in
`zend_persist_property_info` called via `zend_persist_class_entry`
through the inheritance cache.

We shouldn't JIT the property hook code when persisting property info
for the inheritance cache.

This is a simple workaround by temporarily disabling the JIT so that the
property hook code is not JITted when persisting the property info.

An alternative solution would be to move the JITting of the property
hooks to a different place in zend_persist.c by doing an additional pass
over the classes.

Closes GH-15819.

Author: nielsdos

NEWS

@@ -2,6 +2,9 @@ PHP                                                                        NEWS
 |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 ?? ??? ????, PHP 8.4.0RC1
 
+- Opcache:
+  . Fixed bug GH-15657 (Segmentation fault in dasm_x86.h). (nielsdos)
+
 12 Sep 2024, PHP 8.4.0beta5
 
 - BCMath:

ext/opcache/ZendAccelerator.c

@@ -2428,9 +2428,22 @@ static zend_class_entry* zend_accel_inheritance_cache_add(zend_class_entry *ce,
 		} ZEND_HASH_FOREACH_END();
 		ZCG(mem) = (char*)ZCG(mem) + zend_hash_num_elements(dependencies) * sizeof(zend_class_dependency);
 	}
+
+	/* See GH-15657: `zend_persist_class_entry` can JIT property hook code via
+	 * `zend_persist_property_info`, but the inheritance cache should not
+	 * JIT those at this point in time. */
+#ifdef HAVE_JIT
+	bool jit_on_old = JIT_G(on);
+	JIT_G(on) = false;
+#endif
+
 	entry->ce = new_ce = zend_persist_class_entry(ce);
 	zend_update_parent_ce(new_ce);
 
+#ifdef HAVE_JIT
+	JIT_G(on) = jit_on_old;
+#endif
+
 	entry->num_warnings = EG(num_errors);
 	entry->warnings = zend_persist_warnings(EG(num_errors), EG(errors));
 	entry->next = proto->inheritance_cache;

ext/opcache/tests/jit/gh15657.phpt

@@ -0,0 +1,22 @@
+--TEST--
+GH-15657 (Segmentation fault in ext/opcache/jit/ir/dynasm/dasm_x86.h)
+--EXTENSIONS--
+opcache
+--INI--
+opcache.jit_buffer_size=64M
+opcache.jit=1101
+--FILE--
+<?php
+// Triggering the inheritance cache via implementing this interface is important to reproduce the bug
+interface I {}
+
+class A implements I {
+    private $_prop;
+    public $prop {
+        get => $this->_prop;
+    }
+}
+echo "Done\n";
+?>
+--EXPECT--
+Done