Introduce <pointer_guard.h>, extracted from <sysdep.h>

This allows us to define a generic no-op version of PTR_MANGLE and
PTR_DEMANGLE.  In the future, we can use PTR_MANGLE and PTR_DEMANGLE
unconditionally in C sources, avoiding an unintended loss of hardening
due to missing include files or unlucky header inclusion ordering.

In i386 and x86_64, we can avoid a <tls.h> dependency in the C
code by using the computed constant from <tcb-offsets.h>.  <sysdep.h>
no longer includes these definitions, so there is no cyclic dependency
anymore when computing the <tcb-offsets.h> constants.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

3 files changed, 50 insertions, 28 deletions

diff --git a/sysdeps/unix/sysv/linux/i386/____longjmp_chk.S b/sysdeps/unix/sysv/linux/i386/____longjmp_chk.S
index a1cf9a4b21..f409542a62 100644
--- a/sysdeps/unix/sysv/linux/i386/____longjmp_chk.S
+++ b/sysdeps/unix/sysv/linux/i386/____longjmp_chk.S
@@ -16,6 +16,7 @@
    <https://www.gnu.org/licenses/>.  */
 
 #include <sysdep.h>
+#include <pointer_guard.h>
 #include <jmpbuf-offsets.h>
 #include <jmp_buf-ssp.h>
 #include <asm-syntax.h>
diff --git a/sysdeps/unix/sysv/linux/i386/pointer_guard.h b/sysdeps/unix/sysv/linux/i386/pointer_guard.h
new file mode 100644
index 0000000000..a2d2a0c38b
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/i386/pointer_guard.h
@@ -0,0 +1,49 @@
+/* Pointer obfuscation implenentation.  i386 version.
+   Copyright (C) 2005-2022 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef POINTER_GUARD_H
+#define POINTER_GUARD_H
+
+#include <tcb-offsets.h>
+
+#if IS_IN (rtld)
+/* We cannot use the thread descriptor because in ld.so we use setjmp
+   earlier than the descriptor is initialized.  Using a global variable
+   is too complicated here since we have no PC-relative addressing mode.  */
+# include <sysdeps/generic/pointer_guard.h>
+#else
+# ifdef __ASSEMBLER__
+#  define PTR_MANGLE(reg)       xorl %gs:POINTER_GUARD, reg;                  \
+                                roll $9, reg
+#  define PTR_DEMANGLE(reg)     rorl $9, reg;                                 \
+                                xorl %gs:POINTER_GUARD, reg
+# else
+#  define PTR_MANGLE(var)       asm ("xorl %%gs:%c2, %0\n"                    \
+                                     "roll $9, %0"                            \
+                                     : "=r" (var)                             \
+                                     : "0" (var),                             \
+                                       "i" (POINTER_GUARD))
+#  define PTR_DEMANGLE(var)     asm ("rorl $9, %0\n"                          \
+                                     "xorl %%gs:%c2, %0"                      \
+                                     : "=r" (var)                             \
+                                     : "0" (var),                             \
+                                       "i" (POINTER_GUARD))
+# endif
+#endif
+
+#endif /* POINTER_GUARD_H */
diff --git a/sysdeps/unix/sysv/linux/i386/sysdep.h b/sysdeps/unix/sysv/linux/i386/sysdep.h
index 7085f7e19a..b8be668a42 100644
--- a/sysdeps/unix/sysv/linux/i386/sysdep.h
+++ b/sysdeps/unix/sysv/linux/i386/sysdep.h
@@ -446,34 +446,6 @@ struct libc_do_syscall_args
 
 #endif	/* __ASSEMBLER__ */
 
-
-/* Pointer mangling support.  */
-#if IS_IN (rtld)
-/* We cannot use the thread descriptor because in ld.so we use setjmp
-   earlier than the descriptor is initialized.  Using a global variable
-   is too complicated here since we have no PC-relative addressing mode.  */
-#else
-# ifdef __ASSEMBLER__
-#  define PTR_MANGLE(reg)	xorl %gs:POINTER_GUARD, reg;		      \
-				roll $9, reg
-#  define PTR_DEMANGLE(reg)	rorl $9, reg;				      \
-				xorl %gs:POINTER_GUARD, reg
-# else
-#  define PTR_MANGLE(var)	asm ("xorl %%gs:%c2, %0\n"		      \
-				     "roll $9, %0"			      \
-				     : "=r" (var)			      \
-				     : "0" (var),			      \
-				       "i" (offsetof (tcbhead_t,	      \
-						      pointer_guard)))
-#  define PTR_DEMANGLE(var)	asm ("rorl $9, %0\n"			      \
-				     "xorl %%gs:%c2, %0"		      \
-				     : "=r" (var)			      \
-				     : "0" (var),			      \
-				       "i" (offsetof (tcbhead_t,	      \
-						      pointer_guard)))
-# endif
-#endif
-
 /* Each shadow stack slot takes 4 bytes.  Assuming that each stack
    frame takes 128 bytes, this is used to compute shadow stack size
    from stack size.  */