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Re: [PATCH] i386 TLS_INIT_TP might produce bogus asm changing stack pointer.
- From: Mark Wielaard <mjw at redhat dot com>
- To: Florian Weimer <fweimer at redhat dot com>
- Cc: libc-alpha at sourceware dot org, Siddhesh Poyarekar <siddhesh at redhat dot com>
- Date: Tue, 26 Aug 2014 14:27:21 +0200
- Subject: Re: [PATCH] i386 TLS_INIT_TP might produce bogus asm changing stack pointer.
- Authentication-results: sourceware.org; auth=none
- References: <1409041665-1558-1-git-send-email-mjw at redhat dot com> <53FC469A dot 2010701 at redhat dot com>
On Tue, 2014-08-26 at 10:34 +0200, Florian Weimer wrote:
> On 08/26/2014 10:27 AM, Mark Wielaard wrote:
> > * sysdeps/i386/nptl/tls.h (TLS_INIT_TP): Use INTERNAL_SYSCALL
> > to call set_thread_area instead of hand written asm.
>
> Patch looks good, but you can remove these #defines now:
>
> # 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
>
> (INTERNAL_SYSCALL is not affected by this issue because it uses explicit
> register constraints, and not the general "r" constraint.)
Yes, you are right. There were some more defines around that block that
are also no longer used. I removed them all (and made sure everything
still builds of course). Updated commit attached.
Thanks,
Mark
From f8ce6debd1aea3265f7e8bb1ea898d263ac7c76f Mon Sep 17 00:00:00 2001
From: Mark Wielaard <mjw@redhat.com>
Date: Tue, 26 Aug 2014 09:57:56 +0200
Subject: [PATCH] i386 TLS_INIT_TP might produce bogus asm changing stack
pointer.
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.
https://bugzilla.redhat.com/show_bug.cgi?id=1133134
* 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 | 10 ++++++++++
sysdeps/i386/nptl/tls.h | 31 ++-----------------------------
2 files changed, 12 insertions(+), 29 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index 4d2eb52..2eefb33 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2014-08-26 Mark Wielaard <mjw@redhat.com>
+
+ * 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.
+
2014-08-21 Siddhesh Poyarekar <siddhesh@redhat.com>
* nptl/Makefile (CFLAGS-pthread_atfork.c): Remove.
diff --git a/sysdeps/i386/nptl/tls.h b/sysdeps/i386/nptl/tls.h
index ac9c9a2..d7302ba 100644
--- a/sysdeps/i386/nptl/tls.h
+++ b/sysdeps/i386/nptl/tls.h
@@ -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