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[PATCH] x86: Use pad in pthread_unwind_buf to preserve shadow stack register
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: Florian Weimer <fw at deneb dot enyo dot de>
- Cc: Joseph Myers <joseph at codesourcery dot com>, "Carlos O'Donell" <carlos at redhat dot com>, "Tsimbalist, Igor V" <igor dot v dot tsimbalist at intel dot com>, GNU C Library <libc-alpha at sourceware dot org>
- Date: Fri, 30 Mar 2018 10:41:41 -0700
- Subject: [PATCH] x86: Use pad in pthread_unwind_buf to preserve shadow stack register
On Thu, Mar 29, 2018 at 1:20 PM, Florian Weimer <fw@deneb.enyo.de> wrote:
> * H. J. Lu:
>
>> On Thu, Mar 29, 2018 at 1:15 PM, Florian Weimer <fw@deneb.enyo.de> wrote:
>>> * H. J. Lu:
>>>
>>>> You need to make a choice. You either don't introduce a new symbol
>>>> version or don't save shadow stack for thread cancellation. You
>>>> can't have both.
>>>
>>> I don't understand. We have room to save the shadow stack pointer in
>>> the existing struct.
>>
>> No, we don't have room in struct pthread_unwind_buf:
>>
>> Note: There is an unused pointer space in pthread_unwind_buf_data. But
>> it isn't suitable for saving and restoring shadow stack register since
>> x32 is a 64-bit process with 32-bit software pointer and kernel may
>> place x32 shadow stack above 4GB. We need to save and restore 64-bit
>> shadow stack register for x32.
>
> We have for void * fields. They are subsequently overwritten by
> __pthread_register_cancel. But __sigsetjmp can write to them first
> without causing any harm. We just need a private __longjmp_cancel
> that doesn't restore the shadow stack pointer.
Here is the patch which does that. Any comments?
Thanks.
--
H.J.
From f222537447f5ec879427f318b7c0396362b7453a Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Sat, 24 Feb 2018 17:23:54 -0800
Subject: [PATCH] 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.
* 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 (_JUMP_BUF_SIGSET_NSIG):
Changed to 97.
* 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.
---
nptl/pthread_create.c | 9 ++--
setjmp/longjmp.c | 2 +
sysdeps/unix/sysv/linux/x86/setjmpP.h | 4 +-
sysdeps/x86/Makefile | 4 ++
sysdeps/x86/__longjmp_cancel.S | 20 ++++++++
sysdeps/x86/longjmp.c | 45 ++++++++++++++++
sysdeps/x86/nptl/pt-longjmp.c | 97 +++++++++++++++++++++++++++++++++++
7 files changed, 176 insertions(+), 5 deletions(-)
create mode 100644 sysdeps/x86/__longjmp_cancel.S
create mode 100644 sysdeps/x86/longjmp.c
create mode 100644 sysdeps/x86/nptl/pt-longjmp.c
diff --git a/nptl/pthread_create.c b/nptl/pthread_create.c
index caaf07c134..1c5b3780c6 100644
--- a/nptl/pthread_create.c
+++ b/nptl/pthread_create.c
@@ -427,12 +427,15 @@ START_THREAD_DEFN
compilers without that support we do use setjmp. */
struct pthread_unwind_buf unwind_buf;
- /* No previous handlers. */
+ int not_first_call;
+ not_first_call = setjmp ((struct __jmp_buf_tag *) unwind_buf.cancel_jmp_buf);
+
+ /* No previous handlers. NB: This must be done after setjmp since
+ the same space may be used by setjmp to store extra data which
+ should never be used by __libc_unwind_longjmp. */
unwind_buf.priv.data.prev = NULL;
unwind_buf.priv.data.cleanup = NULL;
- int not_first_call;
- not_first_call = setjmp ((struct __jmp_buf_tag *) unwind_buf.cancel_jmp_buf);
if (__glibc_likely (! not_first_call))
{
/* Store the new cleanup handler info. */
diff --git a/setjmp/longjmp.c b/setjmp/longjmp.c
index a2a7065a85..453889e103 100644
--- a/setjmp/longjmp.c
+++ b/setjmp/longjmp.c
@@ -40,9 +40,11 @@ __libc_siglongjmp (sigjmp_buf env, int val)
}
#ifndef __libc_siglongjmp
+# ifndef __libc_longjmp
/* __libc_longjmp is a private interface for cancellation implementation
in libpthread. */
strong_alias (__libc_siglongjmp, __libc_longjmp)
+# endif
weak_alias (__libc_siglongjmp, _longjmp)
weak_alias (__libc_siglongjmp, longjmp)
weak_alias (__libc_siglongjmp, siglongjmp)
diff --git a/sysdeps/unix/sysv/linux/x86/setjmpP.h b/sysdeps/unix/sysv/linux/x86/setjmpP.h
index c0ed767a0d..90a6bbcf32 100644
--- a/sysdeps/unix/sysv/linux/x86/setjmpP.h
+++ b/sysdeps/unix/sysv/linux/x86/setjmpP.h
@@ -22,8 +22,8 @@
#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
+ Define it to 97 to leave some rooms for future use. */
+#define _JUMP_BUF_SIGSET_NSIG 97
/* Number of longs to hold all signals. */
#define _JUMP_BUF_SIGSET_NWORDS \
((_JUMP_BUF_SIGSET_NSIG - 1 + 7) / (8 * sizeof (unsigned long int)))
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..7eb8651cfe
--- /dev/null
+++ b/sysdeps/x86/nptl/pt-longjmp.c
@@ -0,0 +1,97 @@
+/* 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/>. */
+
+/* <nptl/descr.h> has
+
+struct pthread_unwind_buf
+{
+ struct
+ {
+ __jmp_buf jmp_buf;
+ int mask_was_saved;
+ } cancel_jmp_buf[1];
+
+ union
+ {
+ void *pad[4];
+ struct
+ {
+ struct pthread_unwind_buf *prev;
+ struct _pthread_cleanup_buffer *cleanup;
+ int canceltype;
+ } data;
+ } priv;
+};
+
+ The pad array in struct pthread_unwind_buf is used by setjmp to save
+ shadow stack register. Assert that size of struct pthread_unwind_buf
+ is no less than offset of shadow stack pointer plus shadow stack
+ pointer size.
+
+ NB: setjmp is called in libpthread to save shadow stack register. But
+ __libc_unwind_longjmp doesn't restore shadow stack register since they
+ never return after longjmp. */
+
+#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
+
+_Static_assert ((sizeof (struct pthread_unwind_buf)
+ >= (SHADOW_STACK_POINTER_OFFSET
+ + SHADOW_STACK_POINTER_SIZE)),
+ "size of struct pthread_unwind_buf < "
+ "(SHADOW_STACK_POINTER_OFFSET + SHADOW_STACK_POINTER_SIZE)");
+
+#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
--
2.14.3