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Re: [PATCH] Revert Intel CET changes to __jmp_buf_tag (Bug 22743)
On Thu, Jan 25, 2018 at 1:47 AM, Florian Weimer <fweimer@redhat.com> wrote:
> On 01/25/2018 06:33 AM, H.J. Lu wrote:
>
>> Please don't revert my patch. Please try this patch:
>>
>>
>> https://sourceware.org/git/?p=glibc.git;a=commit;h=4b7fc470a6740808b41502d7431f91805e272d26
>>
>> instead. I will clean it up and submit it tomorrow.
>
>
> I don't see how adding a symbol version to pthread_create helps to solve the
> general case. Callers of pthread_register_cancel and pthread_create are
> often compiled at different times. Not everyone does a mass rebuild each
> time they switch to a new glibc version.
True. We just need to use the older struct pthread_unwind_buf when shadow
stack is disabled.
> I still think you are over-engineering this. The pad array has still an
> unused member (the last one). Just change sigsetjmp to store the shadow
> pointer in that location, then the old and new setjmp will work with the
> current stack layout. As far as I can tell, there are only 64 signals, so
> you don't even have to change the location of the signal mask.
No, it doesn't work. struct pthread_unwind_buf is placed on caller's stack
and its address is passed from applications to libpthread. If the size of
caller's struct pthread_unwind_buf is smaller than what libpthread expects,
libpthread will override caller's stack.
> Furthermore, nothing in the toolchain prevents people from compiling
That is not true. From CET spec:
https://github.com/hjl-tools/x86-psABI/wiki/x86-64-psABI-cet.pdf
On a SHSTK capable processor, the following steps should be taken:
1. When loading an executable without interpreter, enable and lock SHSTK if
GNU_PROPERTY_X86_FEATURE_1_SHSTK is set on the executable.
2. When loading an executable with an interpreter, enable SHSTK
if GNU_PROPERTY_X86_FEATURE_1_SHSTK is set on
the interpreter. The interpreter should disable SHSTK if
GNU_PROPERTY_X86_FEATURE_1_SHSTK isn’t set or any shared
objects loaded via the DT_NEEDED tag, otherwise lock SHSTK.
3. After SHSTK is enabled, it is an error to load a shared object without
GNU_PROPERTY_X86_FEATURE_1_SHSTK.
> CET-marked binaries with older glibc headers, so you can't use CET markup to
> determine the size of the stack allocation anyway.
>
Yes, we can.
We enable shadow stack at run-time only if program and all used shared
objects, including dlopened ones, are shadow stack enabled, which means
that they must be compiled with GCC 8 or above and glibc 2.27 or above.
Since we need to save and restore shadow stack only if shadow stack is
enabled, we can safely assume that caller is compiled with smaller
struct pthread_unwind_buf on stack if shadow stack isn't enabled at
run-time. For callers with larger struct pthread_unwind_buf, but
shadow stack isn't enabled, we just have some unused space on caller's
stack.
Here is the patch to do that, Andrew, please work with Debian to verify
that fixes the crash.
BTW, my patch is on hjl/pr22743/master branch in glibc git repo.
Thanks.
--
H.J.
From 10bba58b7eece4eac0db07c100217b709efd4727 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Wed, 24 Jan 2018 15:27:49 -0800
Subject: [PATCH] nptl: Update struct pthread_unwind_buf [BZ #22743]
In glibc 2.27, the size of cancel_jmp_buf in struct pthread_unwind_buf
has been increased to match the size of __jmp_buf_tag on Linux/x86 in
order to save and restore shadow stack. Struct pthread_unwind_buf is
used in <pthread.h>, whose address is passed from applications to
libpthread. To access the private data in struct pthread_unwind_buf,
which is placed after cancel_jmp_buf, in libpthread, we must know which
struct pthread_unwind_buf, before glibc 27 and after glibc 2.27, is used
in caller. If the size of caller's struct pthread_unwind_buf is smaller
than what libpthread expects, libpthread will override caller's stack
since struct pthread_unwind_buf is placed on caller's stack.
We enable shadow stack at run-time only if program and all used shared
objects, including dlopened ones, are shadow stack enabled, which means
that they must be compiled with GCC 8 or above and glibc 2.27 or above.
Since we need to save and restore shadow stack only if shadow stack is
enabled, we can safely assume that caller is compiled with smaller
struct pthread_unwind_buf on stack if shadow stack isn't enabled at
run-time. For callers with larger struct pthread_unwind_buf, but
shadow stack isn't enabled, we just have some unused space on caller's
stack.
struct pthread_unwind_buf is changed to union of
1. struct cancel_jmp_buf[1], which contains the common fields of struct
updated_pthread_unwind_buf and struct compat_pthread_unwind_buf.
2. struct updated_pthread_unwind_buf, which is the updated layout of
the cleanup buffer.
3. struct compat_pthread_unwind_buf, which is the compatible layout of
the cleanup buffer.
A macro, UNWIND_BUF_PRIV, is added to get the pointer to the priv field.
By default, it uses the priv field of struct compat_pthread_unwind_buf.
If a target defines NEED_SAVED_MASK_IN_CANCEL_JMP_BUF, it must provide
its own version of UNEIND_BUF_PRIV to get the pointer to the priv field.
On Linux/x86, it uses the priv field of struct compat_pthread_unwind_buf
if shadow stack is disabled and struct updated_pthread_unwind_buf if
shadow stack is enabled.
[BZ #22743]
* csu/libc-start.c (LIBC_START_MAIN): Use the updated version
of the cleanup buffer.
* nptl/cleanup.c (__pthread_register_cancel): Use UNWIND_BUF_PRIV
to access the priv field in the cleanup buffer.
(__pthread_unregister_cancel): Likewise.
* nptl/cleanup_defer.c (__pthread_register_cancel_defer):
Likewise.
(__pthread_unregister_cancel_restore): Likewise.
* nptl/unwind.c (unwind_stop): Likewise.
(__pthread_unwind_next): Likewise.
* nptl/descr.h (pthread_unwind_buf_data): New.
(updated_pthread_unwind_buf): Likewise.
(compat_pthread_unwind_buf): Likewise.
(pthread_unwind_buf): Updated to use updated_pthread_unwind_buf
and compat_pthread_unwind_buf.
(UNWIND_BUF_PRIV): New. Macro to get pointer to the priv field
in the cleanup buffer.
* nptl/pthread_create.c (START_THREAD_DEFN): Use the updated
version of the cleanup buffer.
(__pthread_create_2_1): Use THREAD_COPY_ADDITONAL_INFO to copy
additonal info if defined.
* sysdeps/unix/sysv/linux/x86/nptl/pthreadP.h: Use the updated
version of the cleanup buffer to check cancel_jmp_buf size.
* sysdeps/unix/sysv/linux/x86/pthreaddef.h
(THREAD_COPY_ADDITONAL_INFO): New.
(UNWIND_BUF_PRIV): Likewise.
---
csu/libc-start.c | 6 ++-
nptl/cleanup.c | 10 ++--
nptl/cleanup_defer.c | 18 ++++---
nptl/descr.h | 75 ++++++++++++++++++++++-------
nptl/pthread_create.c | 9 +++-
nptl/unwind.c | 6 ++-
sysdeps/unix/sysv/linux/x86/nptl/pthreadP.h | 2 +-
sysdeps/unix/sysv/linux/x86/pthreaddef.h | 14 ++++++
8 files changed, 106 insertions(+), 34 deletions(-)
diff --git a/csu/libc-start.c b/csu/libc-start.c
index 605222fa3f..44333446f2 100644
--- a/csu/libc-start.c
+++ b/csu/libc-start.c
@@ -298,8 +298,10 @@ LIBC_START_MAIN (int (*main) (int, char **, char ** MAIN_AUXVEC_DECL),
struct pthread *self = THREAD_SELF;
/* Store old info. */
- unwind_buf.priv.data.prev = THREAD_GETMEM (self, cleanup_jmp_buf);
- unwind_buf.priv.data.cleanup = THREAD_GETMEM (self, cleanup);
+ unwind_buf.updated.priv.data.prev
+ = THREAD_GETMEM (self, cleanup_jmp_buf);
+ unwind_buf.updated.priv.data.cleanup
+ = THREAD_GETMEM (self, cleanup);
/* Store the new cleanup handler info. */
THREAD_SETMEM (self, cleanup_jmp_buf, &unwind_buf);
diff --git a/nptl/cleanup.c b/nptl/cleanup.c
index d21b86e88b..403ffc9fc5 100644
--- a/nptl/cleanup.c
+++ b/nptl/cleanup.c
@@ -28,8 +28,10 @@ __pthread_register_cancel (__pthread_unwind_buf_t *buf)
struct pthread *self = THREAD_SELF;
/* Store old info. */
- ibuf->priv.data.prev = THREAD_GETMEM (self, cleanup_jmp_buf);
- ibuf->priv.data.cleanup = THREAD_GETMEM (self, cleanup);
+ UNWIND_BUF_PRIV (self, ibuf)->data.prev
+ = THREAD_GETMEM (self, cleanup_jmp_buf);
+ UNWIND_BUF_PRIV (self, ibuf)->data.cleanup
+ = THREAD_GETMEM (self, cleanup);
/* Store the new cleanup handler info. */
THREAD_SETMEM (self, cleanup_jmp_buf, (struct pthread_unwind_buf *) buf);
@@ -42,7 +44,9 @@ __cleanup_fct_attribute
__pthread_unregister_cancel (__pthread_unwind_buf_t *buf)
{
struct pthread_unwind_buf *ibuf = (struct pthread_unwind_buf *) buf;
+ struct pthread *self = THREAD_SELF;
- THREAD_SETMEM (THREAD_SELF, cleanup_jmp_buf, ibuf->priv.data.prev);
+ THREAD_SETMEM (self, cleanup_jmp_buf,
+ UNWIND_BUF_PRIV (self, ibuf)->data.prev);
}
hidden_def (__pthread_unregister_cancel)
diff --git a/nptl/cleanup_defer.c b/nptl/cleanup_defer.c
index 5701ce4213..20ace3272a 100644
--- a/nptl/cleanup_defer.c
+++ b/nptl/cleanup_defer.c
@@ -28,8 +28,10 @@ __pthread_register_cancel_defer (__pthread_unwind_buf_t *buf)
struct pthread *self = THREAD_SELF;
/* Store old info. */
- ibuf->priv.data.prev = THREAD_GETMEM (self, cleanup_jmp_buf);
- ibuf->priv.data.cleanup = THREAD_GETMEM (self, cleanup);
+ UNWIND_BUF_PRIV (self, ibuf)->data.prev
+ = THREAD_GETMEM (self, cleanup_jmp_buf);
+ UNWIND_BUF_PRIV (self, ibuf)->data.cleanup
+ = THREAD_GETMEM (self, cleanup);
int cancelhandling = THREAD_GETMEM (self, cancelhandling);
@@ -49,9 +51,9 @@ __pthread_register_cancel_defer (__pthread_unwind_buf_t *buf)
cancelhandling = curval;
}
- ibuf->priv.data.canceltype = (cancelhandling & CANCELTYPE_BITMASK
- ? PTHREAD_CANCEL_ASYNCHRONOUS
- : PTHREAD_CANCEL_DEFERRED);
+ UNWIND_BUF_PRIV (self, ibuf)->data.canceltype
+ = (cancelhandling & CANCELTYPE_BITMASK
+ ? PTHREAD_CANCEL_ASYNCHRONOUS : PTHREAD_CANCEL_DEFERRED);
/* Store the new cleanup handler info. */
THREAD_SETMEM (self, cleanup_jmp_buf, (struct pthread_unwind_buf *) buf);
@@ -65,10 +67,12 @@ __pthread_unregister_cancel_restore (__pthread_unwind_buf_t *buf)
struct pthread *self = THREAD_SELF;
struct pthread_unwind_buf *ibuf = (struct pthread_unwind_buf *) buf;
- THREAD_SETMEM (self, cleanup_jmp_buf, ibuf->priv.data.prev);
+ THREAD_SETMEM (self, cleanup_jmp_buf,
+ UNWIND_BUF_PRIV (self, ibuf)->data.prev);
int cancelhandling;
- if (ibuf->priv.data.canceltype != PTHREAD_CANCEL_DEFERRED
+ if ((UNWIND_BUF_PRIV (self, ibuf)->data.canceltype
+ != PTHREAD_CANCEL_DEFERRED)
&& ((cancelhandling = THREAD_GETMEM (self, cancelhandling))
& CANCELTYPE_BITMASK) == 0)
{
diff --git a/nptl/descr.h b/nptl/descr.h
index 1cc6b09d1e..a30d4fe010 100644
--- a/nptl/descr.h
+++ b/nptl/descr.h
@@ -55,11 +55,30 @@
/ PTHREAD_KEY_2NDLEVEL_SIZE)
+/* Private data in the cleanup buffer. */
+union pthread_unwind_buf_data
+{
+ /* This is the placeholder of the public version. */
+ void *pad[4];
+
+ struct
+ {
+ /* Pointer to the previous cleanup buffer. */
+ struct pthread_unwind_buf *prev;
+ /* Backward compatibility: state of the old-style cleanup
+ handler at the time of the previous new-style cleanup handler
+ installment. */
+ struct _pthread_cleanup_buffer *cleanup;
-/* Internal version of the buffer to store cancellation handler
+ /* Cancellation type before the push call. */
+ int canceltype;
+ } data;
+};
+
+/* Internal updated version of the buffer to store cancellation handler
information. */
-struct pthread_unwind_buf
+struct updated_pthread_unwind_buf
{
struct
{
@@ -70,27 +89,49 @@ struct pthread_unwind_buf
#endif
} cancel_jmp_buf[1];
- union
+ union pthread_unwind_buf_data priv;
+};
+
+/* Internal compatible version of the buffer to store cancellation
+ handler information. */
+struct compat_pthread_unwind_buf
+{
+ struct
{
- /* This is the placeholder of the public version. */
- void *pad[4];
+ __jmp_buf jmp_buf;
+ int mask_was_saved;
+ } cancel_jmp_buf[1];
+
+ union pthread_unwind_buf_data priv;
+};
+/* Internal version of the buffer to store cancellation handler
+ information. */
+struct pthread_unwind_buf
+{
+ union
+ {
+ /* The common fields of updated and compatible versions. */
struct
{
- /* Pointer to the previous cleanup buffer. */
- struct pthread_unwind_buf *prev;
-
- /* Backward compatibility: state of the old-style cleanup
- handler at the time of the previous new-style cleanup handler
- installment. */
- struct _pthread_cleanup_buffer *cleanup;
-
- /* Cancellation type before the push call. */
- int canceltype;
- } data;
- } priv;
+ __jmp_buf jmp_buf;
+ int mask_was_saved;
+ } cancel_jmp_buf[1];
+ struct updated_pthread_unwind_buf updated;
+ struct compat_pthread_unwind_buf compat;
+ };
};
+/* Get pointer to the priv field from THREAD_SELF, "self", and pointer
+ to the cleanup buffer, "p". By default, the compatible version is
+ used. If a target defines NEED_SAVED_MASK_IN_CANCEL_JMP_BUF, it
+ must provide its own version of UNEIND_BUF_PRIV. */
+#ifndef UNWIND_BUF_PRIV
+# ifdef NEED_SAVED_MASK_IN_CANCEL_JMP_BUF
+# error "UNWIND_BUF_PRIV is undefined!"
+# endif
+# define UNWIND_BUF_PRIV(self,p) (&((p)->compat.priv))
+#endif
/* Opcodes and data types for communication with the signal handler to
change user/group IDs. */
diff --git a/nptl/pthread_create.c b/nptl/pthread_create.c
index caaf07c134..77647dcbae 100644
--- a/nptl/pthread_create.c
+++ b/nptl/pthread_create.c
@@ -428,8 +428,8 @@ START_THREAD_DEFN
struct pthread_unwind_buf unwind_buf;
/* No previous handlers. */
- unwind_buf.priv.data.prev = NULL;
- unwind_buf.priv.data.cleanup = NULL;
+ unwind_buf.updated.priv.data.prev = NULL;
+ unwind_buf.updated.priv.data.cleanup = NULL;
int not_first_call;
not_first_call = setjmp ((struct __jmp_buf_tag *) unwind_buf.cancel_jmp_buf);
@@ -701,6 +701,11 @@ __pthread_create_2_1 (pthread_t *newthread, const pthread_attr_t *attr,
THREAD_COPY_POINTER_GUARD (pd);
#endif
+ /* Copy additonal info. */
+#ifdef THREAD_COPY_ADDITONAL_INFO
+ THREAD_COPY_ADDITONAL_INFO (pd);
+#endif
+
/* Verify the sysinfo bits were copied in allocate_stack if needed. */
#ifdef NEED_DL_SYSINFO
CHECK_THREAD_SYSINFO (pd);
diff --git a/nptl/unwind.c b/nptl/unwind.c
index b37a063c53..f58be0ee5f 100644
--- a/nptl/unwind.c
+++ b/nptl/unwind.c
@@ -66,7 +66,8 @@ unwind_stop (int version, _Unwind_Action actions,
/* Handle the compatibility stuff. Execute all handlers
registered with the old method which would be unwound by this
step. */
- struct _pthread_cleanup_buffer *oldp = buf->priv.data.cleanup;
+ struct _pthread_cleanup_buffer *oldp
+ = UNWIND_BUF_PRIV (self, buf)->data.cleanup;
void *cfa = (void *) (_Unwind_Ptr) _Unwind_GetCFA (context);
if (curp != oldp && (do_longjump || FRAME_LEFT (cfa, curp, adj)))
@@ -133,6 +134,7 @@ __pthread_unwind_next (__pthread_unwind_buf_t *buf)
{
struct pthread_unwind_buf *ibuf = (struct pthread_unwind_buf *) buf;
- __pthread_unwind ((__pthread_unwind_buf_t *) ibuf->priv.data.prev);
+ __pthread_unwind ((__pthread_unwind_buf_t *)
+ UNWIND_BUF_PRIV (THREAD_SELF, ibuf)->data.prev);
}
hidden_def (__pthread_unwind_next)
diff --git a/sysdeps/unix/sysv/linux/x86/nptl/pthreadP.h b/sysdeps/unix/sysv/linux/x86/nptl/pthreadP.h
index 247a62e9a0..a3076bf980 100644
--- a/sysdeps/unix/sysv/linux/x86/nptl/pthreadP.h
+++ b/sysdeps/unix/sysv/linux/x86/nptl/pthreadP.h
@@ -23,7 +23,7 @@
extern struct pthread_unwind_buf ____pthread_unwind_buf_private;
-_Static_assert (sizeof (____pthread_unwind_buf_private.cancel_jmp_buf)
+_Static_assert (sizeof (____pthread_unwind_buf_private.updated.cancel_jmp_buf)
>= sizeof (struct __jmp_buf_tag),
"size of cancel_jmp_buf < sizeof __jmp_buf_tag");
diff --git a/sysdeps/unix/sysv/linux/x86/pthreaddef.h b/sysdeps/unix/sysv/linux/x86/pthreaddef.h
index a405a65666..899fcd6743 100644
--- a/sysdeps/unix/sysv/linux/x86/pthreaddef.h
+++ b/sysdeps/unix/sysv/linux/x86/pthreaddef.h
@@ -20,3 +20,17 @@
/* Need saved_mask in cancel_jmp_buf. */
#define NEED_SAVED_MASK_IN_CANCEL_JMP_BUF 1
+
+/* Wee need to copy feature_1 in pthread_create. */
+#define THREAD_COPY_ADDITONAL_INFO(descr) \
+ ((descr)->header.feature_1 \
+ = THREAD_GETMEM (THREAD_SELF, header.feature_1))
+
+/* Use the compatible struct __cancel_jmp_buf_tag if shadow stack is
+ disabled. */
+#undef UNWIND_BUF_PRIV
+#define UNWIND_BUF_PRIV(self,p) \
+ (__extension__ ({ \
+ unsigned int feature_1 = THREAD_GETMEM (self, header.feature_1); \
+ (((feature_1 & (1 << 1)) == 0) \
+ ? &((p)->compat.priv) : &((p)->updated.priv));}))
--
2.14.3