x86: Make a space in jmpbuf for shadow stack pointer

To support Shadow Stack (SHSTK) in Intel Control-flow Enforcement
Technology (CET) in setjmp/longjmp, we need to save shadow stack
pointer in jmp_buf.  The __saved_mask field in jmp_buf has type
of __sigset_t.  On Linux, __sigset_t is defined as

 #define _SIGSET_NWORDS (1024 / (8 * sizeof (unsigned long int)))
typedef struct
{
  unsigned long int __val[_SIGSET_NWORDS];
} __sigset_t;

which is much bigger than expected by the __sigprocmask system call,
which has

typedef struct {
        unsigned long sig[_NSIG_WORDS];
} sigset_t;

For Linux/x86, we can shrink __sigset_t used by __saved_mask in jmp_buf
to add paddings for shadow stack pointer.  As long as the new __sigset_t
is not smaller than sigset_t expected by the __sigprocmask system call,
it should work correctly.

This patch adds an internal header file, <setjmpP.h>, to define
__jmp_buf_sigset_t for __saved_mask in jmp_buf for Linux/x86 with a
space to store shadow stack pointer.  It verifies __jmp_buf_sigset_t has
the suitable size for the __sigprocmask system call.   A run-time test,
tst-saved_mask-1.c, is added to verify that size of __jmp_buf_sigset_t
is sufficient.  If its size is too small, the test fails with

rt_sigprocmask(SIG_SETMASK, strace: umoven: short read (4 < 8) @0x7fa8aa28effc
0x7fa8aa28effc, NULL, 8) = -1 EFAULT (Bad address)
rt_sigprocmask(SIG_SETMASK, strace: umoven: short read (4 < 8) @0x7fa8aa28effc
0x7fa8aa28effc, NULL, 8) = -1 EFAULT (Bad address)
rt_sigprocmask(SIG_SETMASK, NULL, 0x7fa8aa28effc, 8) = -1 EFAULT (Bad address)
exit_group(1)                           = ?

Tested with build-many-glibcs.py.

	* debug/longjmp_chk.c: Include <setjmpP.h> instead of
	<setjmp.h>.
	* setjmp/longjmp.c: Include <setjmpP.h> instead of <setjmp.h>.
	(__libc_siglongjmp): Cast &env[0].__saved_mask to "sigset_t *".
	* setjmp/sigjmp.c: Include <setjmpP.h> instead of <setjmp.h>.
	(__sigjmp_save): Cast &env[0].__saved_mask to "sigset_t *".
	* sysdeps/generic/setjmpP.h: New file.
	* sysdeps/unix/sysv/linux/x86/jmp_buf-ssp.sym: Likewise.
	* sysdeps/unix/sysv/linux/x86/setjmpP.h: Likewise.
	* sysdeps/unix/sysv/linux/x86/tst-saved_mask-1.c: Likewise.
	* sysdeps/unix/sysv/linux/x86/Makefile (gen-as-const-headers):
	Add jmp_buf-ssp.sym.
	(tests): Add tst-saved_mask-1.

1 files changed, 67 insertions, 0 deletions

diff --git a/sysdeps/unix/sysv/linux/x86/setjmpP.h b/sysdeps/unix/sysv/linux/x86/setjmpP.h
new file mode 100644
index 0000000000..69a46d0ce2
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/x86/setjmpP.h
@@ -0,0 +1,67 @@
+/* Internal header file for <setjmp.h>.  Linux/x86 version.
+   Copyright (C) 2017 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
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef	_SETJMPP_H
+#define	_SETJMPP_H	1
+
+#include <bits/types/__sigset_t.h>
+
+/* The biggest signal number + 1.  As of kernel 4.14, x86 _NSIG is 64.
+   Define it to 513 to leave some rooms for future use.  */
+#define _JUMP_BUF_SIGSET_NSIG	513
+/* Number of longs to hold all signals.  */
+#define _JUMP_BUF_SIGSET_NWORDS \
+  ((_JUMP_BUF_SIGSET_NSIG - 1 + 7) / (8 * sizeof (unsigned long int)))
+
+typedef struct
+  {
+    unsigned long int __val[_JUMP_BUF_SIGSET_NWORDS];
+  } __jmp_buf_sigset_t;
+
+typedef union
+  {
+    __sigset_t __saved_mask_compat;
+    struct
+      {
+	__jmp_buf_sigset_t __saved_mask;
+	/* Used for shadow stack pointer.  */
+	unsigned long int __shadow_stack_pointer;
+      } __saved;
+  } __jmpbuf_arch_t;
+
+#undef __sigset_t
+#define __sigset_t __jmpbuf_arch_t
+#include <setjmp.h>
+#undef __saved_mask
+#define __saved_mask __saved_mask.__saved.__saved_mask
+
+#include <signal.h>
+
+#define _SIGPROCMASK_NSIG_WORDS (_NSIG / (8 * sizeof (unsigned long int)))
+
+typedef struct
+  {
+    unsigned long int __val[_SIGPROCMASK_NSIG_WORDS];
+  } __sigprocmask_sigset_t;
+
+extern jmp_buf ___buf;
+extern  __typeof (___buf[0].__saved_mask) ___saved_mask;
+_Static_assert (sizeof (___saved_mask) >= sizeof (__sigprocmask_sigset_t),
+		"size of ___saved_mask < size of __sigprocmask_sigset_t");
+
+#endif /* setjmpP.h  */