From ab4888b207f07fd762c485f94f9543b0ed456a4d Mon Sep 17 00:00:00 2001
From: Mark Wielaard <mjw@redhat.com>
Date: Wed, 27 Aug 2014 17:07:58 +0200
Subject: [PATCH] i386 TLS_INIT_TP might produce bogus asm changing stack
pointer [BZ #17319]
TLS_INIT_TP in sysdeps/i386/nptl/tls.h uses some hand written asm to
generate a set_thread_area that might result in exchanging ebx and esp
around the syscall causing introspection tools like valgrind to loose
track of the user stack. Just use INTERNAL_SYSCALL which makes sure
esp isn't changed arbitrarily.
Before the patch the code would generate:
mov $0xf3,%eax
movl $0xfffff,0x8(%esp)
movl $0x51,0xc(%esp)
xchg %esp,%ebx
int $0x80
xchg %esp,%ebx
Using INTERNAL_SYSCALL instead will generate:
movl $0xfffff,0x8(%esp)
movl $0x51,0xc(%esp)
xchg %ecx,%ebx
mov $0xf3,%eax
int $0x80
xchg %ecx,%ebx
Thanks to Florian Weimer for analysing why the original code generated
the bogus esp usage:
_segdescr.desc happens to be at the top of the stack, so its address
is in %esp. The asm statement says that %3 is an input, so its value
will not change, and GCC can use %esp as the input register for the
expression &_segdescr.desc. But the constraints do not fully describe
the asm statement because the %3 register is actually modified, albeit
only temporarily.
[BZ #17319]
* sysdeps/i386/nptl/tls.h (TLS_INIT_TP): Use INTERNAL_SYSCALL
to call set_thread_area instead of hand written asm.
(__NR_set_thread_area): Removed define.
(TLS_FLAG_WRITABLE): Likewise.
(__ASSUME_SET_THREAD_AREA): Remove check.
(TLS_EBX_ARG): Remove define.
(TLS_LOAD_EBX): Likewise.
---
ChangeLog | 11 +++++++++++
sysdeps/i386/nptl/tls.h | 31 ++-----------------------------
2 files changed, 13 insertions(+), 29 deletions(-)
@@ -1,3 +1,14 @@
+2014-08-27 Mark Wielaard <mjw@redhat.com>
+
+ [BZ #17319]
+ * sysdeps/i386/nptl/tls.h (TLS_INIT_TP): Use INTERNAL_SYSCALL
+ to call set_thread_area instead of hand written asm.
+ (__NR_set_thread_area): Removed define.
+ (TLS_FLAG_WRITABLE): Likewise.
+ (__ASSUME_SET_THREAD_AREA): Remove check.
+ (TLS_EBX_ARG): Remove define.
+ (TLS_LOAD_EBX): Likewise.
+
2014-08-27 Allan McRae <allan@archlinux.org>
* sysdeps/i386/fpu/libm-test-ulps: Update ULPs.
@@ -154,29 +154,6 @@ union user_desc_init
__asm ("movw %w0, %%gs" :: "q" (val))
# endif
-
-# ifndef __NR_set_thread_area
-# define __NR_set_thread_area 243
-# endif
-# ifndef TLS_FLAG_WRITABLE
-# define TLS_FLAG_WRITABLE 0x00000001
-# endif
-
-// XXX Enable for the real world.
-#if 0
-# ifndef __ASSUME_SET_THREAD_AREA
-# error "we need set_thread_area"
-# endif
-#endif
-
-# ifdef __PIC__
-# define TLS_EBX_ARG "r"
-# define TLS_LOAD_EBX "xchgl %3, %%ebx\n\t"
-# else
-# define TLS_EBX_ARG "b"
-# define TLS_LOAD_EBX
-# endif
-
#if defined NEED_DL_SYSINFO
# define INIT_SYSINFO \
_head->sysinfo = GLRO(dl_sysinfo)
@@ -231,12 +208,8 @@ tls_fill_user_desc (union user_desc_init *desc,
tls_fill_user_desc (&_segdescr, -1, _thrdescr); \
\
/* Install the TLS. */ \
- asm volatile (TLS_LOAD_EBX \
- "int $0x80\n\t" \
- TLS_LOAD_EBX \
- : "=a" (_result), "=m" (_segdescr.desc.entry_number) \
- : "0" (__NR_set_thread_area), \
- TLS_EBX_ARG (&_segdescr.desc), "m" (_segdescr.desc)); \
+ INTERNAL_SYSCALL_DECL (err); \
+ _result = INTERNAL_SYSCALL (set_thread_area, err, 1, &_segdescr.desc); \
\
if (_result == 0) \
/* We know the index in the GDT, now load the segment register. \
--
1.9.3