linux-kernel - Re: [uml-devel] [Patch] uml: fix a link error

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Date:	Wed, 4 Feb 2009 21:32:51 +0100 (CET)
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Shane Hathaway <shane@...hawaymix.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Greg Kroah-Hartman <gregkh@...e.de>
cc:	Daolong Wang <ahlongxp@...il.com>,
	User-mode Linux Kernel Development 
	<user-mode-linux-devel@...ts.sourceforge.net>,
	Jeff Dike <jdike@...toit.com>,
	Linux Kernel Development <linux-kernel@...r.kernel.org>,
	Rob Landley <rob@...dley.net>,
	Am?rico Wang <xiyou.wangcong@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>, stable@...nel.org,
	Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>
Subject: Re: [uml-devel] [Patch] uml: fix a link error

On Wed, 4 Feb 2009, Geert Uytterhoeven wrote:
> On Mon, 19 Jan 2009, Shane Hathaway wrote:
> > Daolong Wang wrote:
> > > On Mon, Jan 19, 2009 at 11:21 PM, Jeff Dike <jdike@...toit.com> wrote:
> > >> On Sun, Jan 18, 2009 at 02:23:46PM +0800, Daolong Wang wrote:
> > >>> I can confirm this link error.
> > >> In what environment?  I see no problems here.
> > 
> > I can also confirm this link error.  The problem occurs when compiling
> > either 2.6.28.1 or 2.6.27.12; I didn't try anything earlier.  The patch
> > suggested at this beginning of this thread did solve the link problem
> > and the resulting kernel ran for several hours.  However, I think the
> > patch is still probably incorrect.
> > 
> > I'm going to repost what I said in another message I sent today, this
> > time with a wider audience:
> > 
> > The problem is that the name "sigprocmask" is getting renamed to
> > "kernel_sigprocmask" by a compiler directive in arch/um/Makefile, then
> > that name gets mangled into "sys_kernel_sigprocmask" by the
> > SYSCALL_DEFINE3(sigprocmask, ...) macro in kernel/signal.c.
> > 
> > So, instead of the patch suggested earlier, I added the following line
> > to arch/um/sys-i386/sys_call_table.S:
> > 
> > #define sys_sigprocmask sys_kernel_sigprocmask
> > 
> > This made it compile and link correctly.  Look at the symbols generated
> > by the compile of signal.c to see what I mean:
> > 
> > # nm kernel/signal.o | grep sigprocmask
> > 0000008f r __kstrtab_kernel_sigprocmask
> > 00000040 r __ksymtab_kernel_sigprocmask
> > 00001ea6 T kernel_sigprocmask
> > 00002d67 T sys_kernel_sigprocmask
> > 00001faf T sys_rt_sigprocmask
> > 
> > Unfortunately, it's a mystery to me that others haven't run into this
> > before.  My host environment is RHEL 4 inside some kind of chroot.
> 
> I've just started seeing this problem with some 2.6.29-rc3 kernel...
> 
> Before, I did not have this problem with various 2.6.28-rc8 and 2.6.29-rc1
> kernels (and several older versions I don't remember).
> 
> Given 2.6.29-rc1 works for me and 2.6.28.1 fails for you, I'm inclined to
> believe 2.6.28 is OK. I'll give it a try...
> 
> BTW, I'm using CentOS 5.2.

Following up from home...

Indeed, 2.6.28 works, 2.6.28.1 doesn't.

According to git bisect, it got introduced by the system call security fixes
(CVE-2009-0029), more specifically by this part:

| commit fe7c0d987fb2cce464d29eec9dfcca6296b5eed7
| Author: Heiko Carstens <heiko.carstens@...ibm.com>
| Date:   Wed Jan 14 14:14:06 2009 +0100
| 
|     System call wrappers part 04
|     
|     commit b290ebe2c46d01b742b948ce03f09e8a3efb9a92 upstream.
|     
|     Signed-off-by: Heiko Carstens <heiko.carstens@...ibm.com>
|     Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
| 
| --- a/kernel/signal.c
| +++ b/kernel/signal.c
| @@ -2425,8 +2424,8 @@ sys_sigpending(old_sigset_t __user *set)
|  /* Some platforms have their own version with special arguments others
|     support only sys_rt_sigprocmask.  */
|  
| -asmlinkage long
| -sys_sigprocmask(int how, old_sigset_t __user *set, old_sigset_t __user *oset)
   ^^^^^^^^^^^^^^^
| +SYSCALL_DEFINE3(sigprocmask, int, how, old_sigset_t __user *, set,
                   ^^^^^^^^^^^
| +		old_sigset_t __user *, oset)
|  {
|  	int error;
|  	old_sigset_t old_set, new_set;

Hence it allows sigprocmask to be redefined to kernel_sigprocmask by the C
preprocessor...

This got backported to 2.6.27.12 as well, confusing people who ran post-2.6.27
development kernels and never noticed the problem (including Jeff and me)...

It showed up in a "development" kernel in 2.6.29-rc2 only.

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds
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