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[PATCH 2/2] jmpbuf: Add paddings for target specific usage


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;

We can shrink __sigset_t used by __saved_mask in jmp_buf to add paddings
for target specific usage.  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 defines __jmp_buf_sigset_t for __saved_mask in
jmp_buf on Linux and verifies __jmp_buf_sigset_t has the suitable size
for the __sigprocmask system call.

Tested with build-many-glibcs.py.

OK for master?

H.J.
---
	* bits/setjmp3.h: New file.
	* sysdeps/unix/sysv/linux/bits/setjmp3.h: Likewise.
	* setjmp/Makefile (headers): Add bits/setjmp3.h.
	* setjmp/longjmp.c (__libc_siglongjmp): Cast &env[0].__saved_mask
	to "sigset_t *".
	* setjmp/sigjmp.c (__sigjmp_save): Likewise.
	* sysdeps/powerpc/longjmp.c (__vmx__libc_siglongjmp): Likewise.
	* sysdeps/powerpc/novmx-longjmp.c (__novmx__libc_siglongjmp):
	Likewise.
	* sysdeps/powerpc/novmx-sigjmp.c (__novmx__sigjmp_save): Likewise.
	* sysdeps/powerpc/sigjmp.c (__vmx__sigjmp_save): Likewise.
	* sysdeps/unix/sysv/linux/ia64/unwind_longjmp.c
	(__libc_unwind_longjmp): Likewise.
	* setjmp/setjmp.h: Include <bits/setjmp3.h> instead of
	<bits/types/__sigset_t.h>.
	(__jmp_buf_tag): Change __saved_mask to __target.
	* setjmp/tst-jmp_buf.c: Include <signal.h>.
	[_NSIG] (KERNEL_NSIG_WORDS): New.
	[_NSIG] (kernel_sigset_t): Likewise.
	[_NSIG] (do_test): Add _Static_assert for size of __saved_mask
	in jmp_buf >= sizeof kernel_sigset_t.
---
 bits/setjmp3.h                                | 31 +++++++++++++++++
 setjmp/Makefile                               |  2 +-
 setjmp/longjmp.c                              |  3 +-
 setjmp/setjmp.h                               |  4 +--
 setjmp/sigjmp.c                               |  2 +-
 setjmp/tst-jmp_buf.c                          | 17 ++++++++++
 sysdeps/powerpc/longjmp.c                     |  3 +-
 sysdeps/powerpc/novmx-longjmp.c               |  3 +-
 sysdeps/powerpc/novmx-sigjmp.c                |  2 +-
 sysdeps/powerpc/sigjmp.c                      |  2 +-
 sysdeps/unix/sysv/linux/bits/setjmp3.h        | 48 +++++++++++++++++++++++++++
 sysdeps/unix/sysv/linux/ia64/unwind_longjmp.c |  3 +-
 12 files changed, 110 insertions(+), 10 deletions(-)
 create mode 100644 bits/setjmp3.h
 create mode 100644 sysdeps/unix/sysv/linux/bits/setjmp3.h

diff --git a/bits/setjmp3.h b/bits/setjmp3.h
new file mode 100644
index 0000000000..b164c8d449
--- /dev/null
+++ b/bits/setjmp3.h
@@ -0,0 +1,31 @@
+/* Generic __jmpbuf_target_t defition.
+   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 _SETJMP_H
+# error "Never include <bits/setjmp3.h> directly; use <setjmp.h> instead."
+#endif
+
+#include <bits/types/__sigset_t.h>
+
+typedef struct
+  {
+    __sigset_t __saved_mask;
+  } __jmpbuf_target_t;
+
+/* Saved signal mask.  */
+#define __saved_mask __target.__saved_mask
diff --git a/setjmp/Makefile b/setjmp/Makefile
index 857e0b8d0f..6ab9b4c3ca 100644
--- a/setjmp/Makefile
+++ b/setjmp/Makefile
@@ -22,7 +22,7 @@ subdir	:= setjmp
 
 include ../Makeconfig
 
-headers	:= setjmp.h bits/setjmp.h bits/setjmp2.h
+headers	:= setjmp.h bits/setjmp.h bits/setjmp2.h bits/setjmp3.h
 
 routines	:= setjmp sigjmp bsd-setjmp bsd-_setjmp \
 		   longjmp __longjmp jmp-unwind
diff --git a/setjmp/longjmp.c b/setjmp/longjmp.c
index 2453c2c124..86a024b4b8 100644
--- a/setjmp/longjmp.c
+++ b/setjmp/longjmp.c
@@ -31,7 +31,8 @@ __libc_siglongjmp (sigjmp_buf env, int val)
 
   if (env[0].__mask_was_saved)
     /* Restore the saved signal mask.  */
-    (void) __sigprocmask (SIG_SETMASK, &env[0].__saved_mask,
+    (void) __sigprocmask (SIG_SETMASK,
+			  (sigset_t *) &env[0].__saved_mask,
 			  (sigset_t *) NULL);
 
   /* Call the machine-dependent function to restore machine state.  */
diff --git a/setjmp/setjmp.h b/setjmp/setjmp.h
index 86fb2edf6c..1082fb0142 100644
--- a/setjmp/setjmp.h
+++ b/setjmp/setjmp.h
@@ -27,7 +27,7 @@
 __BEGIN_DECLS
 
 #include <bits/setjmp.h>		/* Get `__jmp_buf'.  */
-#include <bits/types/__sigset_t.h>
+#include <bits/setjmp3.h>
 
 /* Calling environment, plus possibly a saved signal mask.  */
 struct __jmp_buf_tag
@@ -38,7 +38,7 @@ struct __jmp_buf_tag
        or add others before it.  */
     __jmp_buf __jmpbuf;		/* Calling environment.  */
     int __mask_was_saved;	/* Saved the signal mask?  */
-    __sigset_t __saved_mask;	/* Saved signal mask.  */
+    __jmpbuf_target_t __target;	/* Target specific data.  */
   };
 
 
diff --git a/setjmp/sigjmp.c b/setjmp/sigjmp.c
index 30839ae819..0cd733b3ee 100644
--- a/setjmp/sigjmp.c
+++ b/setjmp/sigjmp.c
@@ -28,7 +28,7 @@ __sigjmp_save (sigjmp_buf env, int savemask)
 {
   env[0].__mask_was_saved = (savemask &&
 			     __sigprocmask (SIG_BLOCK, (sigset_t *) NULL,
-					    &env[0].__saved_mask) == 0);
+					    (sigset_t *) &env[0].__saved_mask) == 0);
 
   return 0;
 }
diff --git a/setjmp/tst-jmp_buf.c b/setjmp/tst-jmp_buf.c
index 1b25d85876..16ddebc224 100644
--- a/setjmp/tst-jmp_buf.c
+++ b/setjmp/tst-jmp_buf.c
@@ -18,9 +18,19 @@
 
 #include <stdio.h>
 #include <setjmp.h>
+#include <signal.h>
 #include <stddef.h>
 #include <jmp_buf-macros.h>
 
+#ifdef _NSIG
+# define KERNEL_NSIG_WORDS (_NSIG / (8 * sizeof (unsigned long int)))
+
+typedef struct
+  {
+    unsigned long int __val[KERNEL_NSIG_WORDS];
+  } kernel_sigset_t;
+#endif
+
 #define STR_HELPER(x) #x
 #define STR(x) STR_HELPER(x)
 
@@ -54,6 +64,13 @@ do_test (void)
   TEST_OFFSET (struct __jmp_buf_tag, __saved_mask,
 	       SAVED_MASK_OFFSET);
 
+#ifdef _NSIG
+  jmp_buf buf;
+  __typeof (buf[0].__saved_mask) saved_mask;
+  _Static_assert (sizeof (saved_mask) >= sizeof (kernel_sigset_t),
+		  "size of saved_mask < size of kernel_sigset_t");
+#endif
+
   return 0;
 }
 
diff --git a/sysdeps/powerpc/longjmp.c b/sysdeps/powerpc/longjmp.c
index bd3ed8c22b..a23f2c582b 100644
--- a/sysdeps/powerpc/longjmp.c
+++ b/sysdeps/powerpc/longjmp.c
@@ -39,7 +39,8 @@ __vmx__libc_siglongjmp (sigjmp_buf env, int val)
 
   if (env[0].__mask_was_saved)
     /* Restore the saved signal mask.  */
-    (void) __sigprocmask (SIG_SETMASK, &env[0].__saved_mask,
+    (void) __sigprocmask (SIG_SETMASK,
+			  (sigset_t *) &env[0].__saved_mask,
 			  (sigset_t *) NULL);
 
   /* Call the machine-dependent function to restore machine state.  */
diff --git a/sysdeps/powerpc/novmx-longjmp.c b/sysdeps/powerpc/novmx-longjmp.c
index b0020b728a..662fbc5432 100644
--- a/sysdeps/powerpc/novmx-longjmp.c
+++ b/sysdeps/powerpc/novmx-longjmp.c
@@ -37,7 +37,8 @@ __novmx__libc_siglongjmp (__novmx__sigjmp_buf env, int val)
 
   if (env[0].__mask_was_saved)
     /* Restore the saved signal mask.  */
-    (void) __sigprocmask (SIG_SETMASK, &env[0].__saved_mask,
+    (void) __sigprocmask (SIG_SETMASK,
+			  (sigset_t *) &env[0].__saved_mask,
 			  (sigset_t *) NULL);
 
   /* Call the machine-dependent function to restore machine state.  */
diff --git a/sysdeps/powerpc/novmx-sigjmp.c b/sysdeps/powerpc/novmx-sigjmp.c
index 7d0ae59437..62680fe38f 100644
--- a/sysdeps/powerpc/novmx-sigjmp.c
+++ b/sysdeps/powerpc/novmx-sigjmp.c
@@ -35,7 +35,7 @@ __novmx__sigjmp_save (__novmx__sigjmp_buf env, int savemask)
 {
   env[0].__mask_was_saved = (savemask &&
 			     __sigprocmask (SIG_BLOCK, (sigset_t *) NULL,
-					    &env[0].__saved_mask) == 0);
+					    (sigset_t *) &env[0].__saved_mask) == 0);
 
   return 0;
 }
diff --git a/sysdeps/powerpc/sigjmp.c b/sysdeps/powerpc/sigjmp.c
index 6d593a0992..736491eff9 100644
--- a/sysdeps/powerpc/sigjmp.c
+++ b/sysdeps/powerpc/sigjmp.c
@@ -31,7 +31,7 @@ __vmx__sigjmp_save (sigjmp_buf env, int savemask)
 {
   env[0].__mask_was_saved = (savemask &&
 			     __sigprocmask (SIG_BLOCK, (sigset_t *) NULL,
-					    &env[0].__saved_mask) == 0);
+					    (sigset_t *) &env[0].__saved_mask) == 0);
 
   return 0;
 }
diff --git a/sysdeps/unix/sysv/linux/bits/setjmp3.h b/sysdeps/unix/sysv/linux/bits/setjmp3.h
new file mode 100644
index 0000000000..e86dbdcba4
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/bits/setjmp3.h
@@ -0,0 +1,48 @@
+/* __jmpbuf_target_t defition for Linux.
+   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 _SETJMP_H
+# error "Never include <bits/setjmp3.h> directly; use <setjmp.h> instead."
+#endif
+
+#include <bits/types/__sigset_t.h>
+
+/* The biggest signal number + 1  */
+#define _JUMP_BUF_SIGSET_NSIG	257
+/* 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;
+	/* Paddings for target specific usage.  */
+	unsigned long int __padding[12];
+      } __saved;
+  } __jmpbuf_target_t;
+
+/* Saved signal mask.  */
+#define __saved_mask __target.__saved.__saved_mask
diff --git a/sysdeps/unix/sysv/linux/ia64/unwind_longjmp.c b/sysdeps/unix/sysv/linux/ia64/unwind_longjmp.c
index 874ed18d6b..658a25b87b 100644
--- a/sysdeps/unix/sysv/linux/ia64/unwind_longjmp.c
+++ b/sysdeps/unix/sysv/linux/ia64/unwind_longjmp.c
@@ -34,7 +34,8 @@ __libc_unwind_longjmp (sigjmp_buf env, int val)
 
   if (env[0].__mask_was_saved)
     /* Restore the saved signal mask.  */
-    (void) __sigprocmask (SIG_SETMASK, &env[0].__saved_mask,
+    (void) __sigprocmask (SIG_SETMASK,
+			  (sigset_t *) &env[0].__saved_mask,
 			  (sigset_t *) NULL);
 
   /* Call the machine-dependent function to restore machine state.  */
-- 
2.13.6


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