nptl: Update struct pthread_unwind_buf [BZ #22743]hjl/pr22743/master

In glibc 2.28, 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 register.  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 28 and after glibc 2.28, 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 2.28 or above.
Since we need to save and restore shadow stack register 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
full and struct compat_pthread_unwind_buf.
2. struct full_pthread_unwind_buf, which is the full 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 full_pthread_unwind_buf if shadow
stack is enabled.

Note: There is an unused pointer space in pthread_unwind_buf_data.  But
it isn't unsuitable 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.

	[BZ #22743]
	* csu/libc-start.c (LIBC_START_MAIN): Use the full 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.
	(full_pthread_unwind_buf): Likewise.
	(compat_pthread_unwind_buf): Likewise.
	(pthread_unwind_buf): Updated to use full_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 full
	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 full
	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.

1 files changed, 4 insertions, 2 deletions

diff --git a/csu/libc-start.c b/csu/libc-start.c
index 605222fa3f..c6bbc97ef0 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.full.priv.data.prev
+	= THREAD_GETMEM (self, cleanup_jmp_buf);
+      unwind_buf.full.priv.data.cleanup
+	= THREAD_GETMEM (self, cleanup);
 
       /* Store the new cleanup handler info.  */
       THREAD_SETMEM (self, cleanup_jmp_buf, &unwind_buf);