Add IBT support for fiber

Indirect Branch Tracking (IBT) is part of Intel's Control-Flow
Enforcement Technology (CET). IBT is hardware based, forward edge
Control-Flow-Integrity mechanism where any indirect CALL/JMP must target
an ENDBR instruction or suffer #CP.

This commit adds IBT support for fiber:
1. Add endbr32/64 in assembly
2. Inform compiler jump_fcontext may return via indirect branch

Furthermore:
gcc support CET since v8.1 and set it to default since gcc 11. That is,
the ELF header of sapi/cli/php has a property named IBT. However, such
property is lost since PHP8.1 because the assembly introduced by Fiber.
This commit also fixes this.

Closes GH-8339

Signed-off-by: Chen, Hu <hu1.chen@intel.com>
Co-authored-by: Christoph M. Becker <cmbecker69@gmx.de>

NEWS

@@ -2,6 +2,9 @@ PHP                                                                        NEWS
 |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 ?? ??? ????, PHP 8.1.8
 
+- Core:
+  . Fixed bug GH-8338 (Intel CET is disabled unintentionally). (Chen, Hu)
+
 - MBString:
   . mb_detect_encoding recognizes all letters in Czech alphabet (alexdowad)
   . mb_detect_encoding recognizes all letters in Hungarian alphabet (alexdowad)

Zend/asm/jump_x86_64_sysv_elf_gas.S

@@ -24,12 +24,18 @@
  *                                                                                      *
  ****************************************************************************************/
 
+# if defined __CET__
+#  include <cet.h>
+# else
+#  define _CET_ENDBR
+# endif
 .file "jump_x86_64_sysv_elf_gas.S"
 .text
 .globl jump_fcontext
 .type jump_fcontext,@function
 .align 16
 jump_fcontext:
+    _CET_ENDBR
     leaq  -0x38(%rsp), %rsp /* prepare stack */
 
 #if !defined(BOOST_USE_TSX)

Zend/asm/make_x86_64_sysv_elf_gas.S

@@ -24,12 +24,18 @@
  *                                                                                      *
  ****************************************************************************************/
 
+# if defined __CET__
+#  include <cet.h>
+# else
+#  define _CET_ENDBR
+# endif
 .file "make_x86_64_sysv_elf_gas.S"
 .text
 .globl make_fcontext
 .type make_fcontext,@function
 .align 16
 make_fcontext:
+    _CET_ENDBR
     /* first arg of make_fcontext() == top of context-stack */
     movq  %rdi, %rax
 
@@ -66,11 +72,13 @@ make_fcontext:
 trampoline:
     /* store return address on stack */
     /* fix stack alignment */
+    _CET_ENDBR
     push %rbp
     /* jump to context-function */
     jmp *%rbx
 
 finish:
+    _CET_ENDBR
     /* exit code is zero */
     xorq  %rdi, %rdi
     /* exit application */

Zend/zend_fibers.c

@@ -141,7 +141,7 @@ typedef struct {
 
 /* These functions are defined in assembler files provided by boost.context (located in "Zend/asm"). */
 extern void *make_fcontext(void *sp, size_t size, void (*fn)(boost_context_data));
-extern boost_context_data jump_fcontext(void *to, zend_fiber_transfer *transfer);
+extern ZEND_INDIRECT_RETURN boost_context_data jump_fcontext(void *to, zend_fiber_transfer *transfer);
 #endif
 
 ZEND_API zend_class_entry *zend_ce_fiber;

Zend/zend_portability.h

@@ -679,4 +679,10 @@ extern "C++" {
 # define ZEND_VOIDP(ptr) (ptr)
 #endif
 
+#if defined(__GNUC__) && ZEND_GCC_VERSION >= 9000
+# define ZEND_INDIRECT_RETURN __attribute__((__indirect_return__))
+#else
+# define ZEND_INDIRECT_RETURN
+#endif
+
 #endif /* ZEND_PORTABILITY_H */