x86: Use pad in pthread_unwind_buf to preserve shadow stack register

The pad array in struct pthread_unwind_buf is used by setjmp to save
shadow stack register.  We assert that size of struct pthread_unwind_buf
is no less than offset of shadow stack pointer + shadow stack pointer
size.

Since functions, like LIBC_START_MAIN, START_THREAD_DEFN as well as
these with thread cancellation, call setjmp, but never return after
__libc_unwind_longjmp, __libc_unwind_longjmp, which is defined as
__libc_longjmp on x86, doesn't need to restore shadow stack register.
__libc_longjmp, which is a private interface for thread cancellation
implementation in libpthread, is changed to call __longjmp_cancel,
instead of __longjmp.  __longjmp_cancel is a new internal function
in libc, which is similar to __longjmp, but doesn't restore shadow
stack register.

The compatibility longjmp and siglongjmp in libpthread.so are changed
to call __libc_siglongjmp, instead of __libc_longjmp, so that they will
restore shadow stack register.

Tested with build-many-glibcs.py.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Carlos O'Donell <carlos@redhat.com>

	* nptl/pthread_create.c (START_THREAD_DEFN): Clear previous
	handlers after setjmp.
	* setjmp/longjmp.c (__libc_longjmp): Don't define alias if
	defined.
	* sysdeps/unix/sysv/linux/x86/setjmpP.h: Include
	<libc-pointer-arith.h>.
	(_JUMP_BUF_SIGSET_BITS_PER_WORD): New.
	(_JUMP_BUF_SIGSET_NSIG): Changed to 96.
	(_JUMP_BUF_SIGSET_NWORDS): Changed to use ALIGN_UP and
	_JUMP_BUF_SIGSET_BITS_PER_WORD.
	* sysdeps/x86/Makefile (sysdep_routines): Add __longjmp_cancel.
	* sysdeps/x86/__longjmp_cancel.S: New file.
	* sysdeps/x86/longjmp.c: Likewise.
	* sysdeps/x86/nptl/pt-longjmp.c: Likewise.

4 files changed, 140 insertions, 0 deletions

diff --git a/sysdeps/x86/Makefile b/sysdeps/x86/Makefile
index 0d0326c21a..d25d6f0ae4 100644
--- a/sysdeps/x86/Makefile
+++ b/sysdeps/x86/Makefile
@@ -8,3 +8,7 @@ sysdep-dl-routines += dl-get-cpu-features
 tests += tst-get-cpu-features
 tests-static += tst-get-cpu-features-static
 endif
+
+ifeq ($(subdir),setjmp)
+sysdep_routines += __longjmp_cancel
+endif
diff --git a/sysdeps/x86/__longjmp_cancel.S b/sysdeps/x86/__longjmp_cancel.S
new file mode 100644
index 0000000000..b57dbfa376
--- /dev/null
+++ b/sysdeps/x86/__longjmp_cancel.S
@@ -0,0 +1,20 @@
+/* __longjmp_cancel for x86.
+   Copyright (C) 2018 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/>.  */
+
+#define __longjmp __longjmp_cancel
+#include <__longjmp.S>
diff --git a/sysdeps/x86/longjmp.c b/sysdeps/x86/longjmp.c
new file mode 100644
index 0000000000..a53f31e1dd
--- /dev/null
+++ b/sysdeps/x86/longjmp.c
@@ -0,0 +1,45 @@
+/* __libc_siglongjmp for x86.
+   Copyright (C) 2018 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/>.  */
+
+#define __libc_longjmp __redirect___libc_longjmp
+#include <setjmp/longjmp.c>
+#undef __libc_longjmp
+
+extern void __longjmp_cancel (__jmp_buf __env, int __val)
+     __attribute__ ((__noreturn__)) attribute_hidden;
+
+/* Since __libc_longjmp is a private interface for cancellation
+   implementation in libpthread, there is no need to restore shadow
+   stack register.  */
+
+void
+__libc_longjmp (sigjmp_buf env, int val)
+{
+  /* Perform any cleanups needed by the frames being unwound.  */
+  _longjmp_unwind (env, val);
+
+  if (env[0].__mask_was_saved)
+    /* Restore the saved signal mask.  */
+    (void) __sigprocmask (SIG_SETMASK,
+			  (sigset_t *) &env[0].__saved_mask,
+			  (sigset_t *) NULL);
+
+  /* Call the machine-dependent function to restore machine state
+     without shadow stack.  */
+  __longjmp_cancel (env[0].__jmpbuf, val ?: 1);
+}
diff --git a/sysdeps/x86/nptl/pt-longjmp.c b/sysdeps/x86/nptl/pt-longjmp.c
new file mode 100644
index 0000000000..6165c7d4a7
--- /dev/null
+++ b/sysdeps/x86/nptl/pt-longjmp.c
@@ -0,0 +1,71 @@
+/* ABI compatibility for 'longjmp' and 'siglongjmp' symbols in libpthread ABI.
+   X86 version.
+   Copyright (C) 18 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/>.  */
+
+#include <pthreadP.h>
+#include <jmp_buf-ssp.h>
+
+#ifdef __x86_64__
+# define SHADOW_STACK_POINTER_SIZE 8
+#else
+# define SHADOW_STACK_POINTER_SIZE 4
+#endif
+
+/* Assert that the priv field in struct pthread_unwind_buf has space
+   to store shadow stack pointer.  */
+_Static_assert ((offsetof (struct pthread_unwind_buf, priv)
+		 <= SHADOW_STACK_POINTER_OFFSET)
+		&& ((offsetof (struct pthread_unwind_buf, priv)
+		     + sizeof (((struct pthread_unwind_buf *) 0)->priv))
+		    >= (SHADOW_STACK_POINTER_OFFSET
+			+ SHADOW_STACK_POINTER_SIZE)),
+		"Shadow stack pointer is not within private storage "
+		"of pthread_unwind_buf.");
+
+#include <shlib-compat.h>
+
+/* libpthread once had its own longjmp (and siglongjmp alias), though there
+   was no apparent reason for it.  There is no use in having a separate
+   symbol in libpthread, but the historical ABI requires it.  For static
+   linking, there is no need to provide anything here--the libc version
+   will be linked in.  For shared library ABI compatibility, there must be
+   longjmp and siglongjmp symbols in libpthread.so.
+
+   With an IFUNC resolver, it would be possible to avoid the indirection,
+   but the IFUNC resolver might run before the __libc_longjmp symbol has
+   been relocated, in which case the IFUNC resolver would not be able to
+   provide the correct address.  */
+
+#if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_22)
+
+static void __attribute__ ((noreturn, used))
+longjmp_compat (jmp_buf env, int val)
+{
+  /* NB: We call __libc_siglongjmp,  instead of __libc_longjmp, since
+     __libc_longjmp is a private interface for cancellation which
+     doesn't restore shadow stack register.  */
+  __libc_siglongjmp (env, val);
+}
+
+strong_alias (longjmp_compat, longjmp_alias)
+compat_symbol (libpthread, longjmp_alias, longjmp, GLIBC_2_0);
+
+strong_alias (longjmp_alias, siglongjmp_alias)
+compat_symbol (libpthread, siglongjmp_alias, siglongjmp, GLIBC_2_0);
+
+#endif