[uml-devel] UML + skas

[uml-devel] UML + skas

[jeremie le-hen]

Hi all,

I have just subscribed to this list because I found a strange bug while
compiling an UML within an SKAS'd host.  Here is the problem :

(my host is a 2.4.23 kernel with the SKAS patch released on 2002/11/11)

--- cut here ---

droopy:tmp$ wget -q http://heanet.dl.sourceforge.net/sourceforge/user-mode-linux/uml-patch-2.4.23-1.bz2
droopy:tmp$ bzip2 -d uml-patch-2.4.23-1.bz2 
droopy:tmp$ wget -q http://www.kernel.org/pub/linux/kernel/v2.4/linux-2.4.23.tar.bz2
droopy:tmp$ tar xfj linux-2.4.23.tar.bz2 
droopy:tmp$ cd linux-2.4.23
droopy:linux-2.4.23$ patch -p1 < ../uml-patch-2.4.23-1 
[... no error ...]
droopy:linux-2.4.23$ make menuconfig ARCH=um
[... do not change anything, just quit ...]
droopy:linux-2.4.23$ make dep ARCH=um
[...]
droopy:linux-2.4.23$ make linux ARCH=um
[...]
gcc   -Wall -Wstrict-prototypes -Wno-trigraphs -O2 -fno-strict-aliasing -fno-common -U__i386__ -Ui386 -DUM_FASTCALL -g -D__arch_um__ -DSUBARCH=\"i386\" -D_LARGEFILE64_SOURCE  -I/space/kernel/tmp/linux-2.4.23/arch/um/include -I/space/kernel/tmp/linux-2.4.23/arch/um/kernel/tt/include -I/space/kernel/tmp/linux-2.4.23/arch/um/kernel/skas/include -D_GNU_SOURCE -c -o process.o process.c
[...]
In file included from process.c:27:
/space/kernel/tmp/linux-2.4.23/arch/um/include/skas_ptrace.h:9: redefinition of `struct ptrace_faultinfo'
/space/kernel/tmp/linux-2.4.23/arch/um/include/skas_ptrace.h:14: redefinition of `struct ptrace_ldt'
make[3]: *** [process.o] Error 1
[...]

--- cut here ---


After preprocessing the process.c file, I found that
`struct ptrace_faultinfo' and `struct ptrace_ldt' were first defined
in file `/usr/include/asm/ptrace.h' and then in
`arch/um/include/skas_ptrace.h'.  Since `/usr/include/asm/' is a symlink
in  `/usr/src/linux/` which in turn points to my kernel source, I thought
that it was maybe due to some tricky patch I have applied on my host's
kernel.  So I used a clean kernel source instead, and I made
`/usr/include/asm/' point in it.  And everything compiled perfectly.

Therefore I went through my various patches to see which one modified
`asm-i386/ptrace.h'.  And what a surprise when I saw the following in
`host-skas3.patch' :


--- cut here ---

diff -urN linux-2.4.23/include/asm-i386/ptrace.h linux-2.4.23-host_skas3_20031111/include/asm-i386/ptrace.h
--- linux-2.4.23/include/asm-i386/ptrace.h      2001-09-14 23:04:08.000000000 +0200
+++ linux-2.4.23-host_skas3_20031111/include/asm-i386/ptrace.h  2003-12-04 21:08:46.000000000 +0100
@@ -51,6 +51,22 @@
 
 #define PTRACE_SETOPTIONS         21
 
+struct ptrace_faultinfo {
+       int is_write;
+       unsigned long addr;
+};
+
+struct ptrace_ldt {
+       int func;
+       void *ptr;
+       unsigned long bytecount;
+};
+
+#define PTRACE_FAULTINFO 52
+#define PTRACE_SIGPENDING 53
+#define PTRACE_LDT 54
+#define PTRACE_SWITCH_MM 55

--- cut here ---

This is *exactly* the same content as `arch/um/include/skas_ptrace.h'.
From what I googled, it seems to be a known bug.  But it think it would
not be very difficult to make some #define protection around theses
structures to prevent from changing the destination of `/usr/src/linux/'
to a source without the SKAS patch applied.

Regards,
-- 
Jeremie LE HEN aka TtZ/TataZ                          jeremie.le-hen@epita.fr
                                                                 ttz@epita.fr
Hi! I'm a .signature virus! Copy me into your ~/.signature to help me spread!


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Re: [uml-devel] UML + skas

[BlaisorBlade]

Alle 19:33, martedì 30 dicembre 2003, jeremie le-hen ha scritto:
> Hi all,

> I have just subscribed to this list because I found a strange bug while
> compiling an UML within an SKAS'd host.  Here is the problem :
>
> (my host is a 2.4.23 kernel with the SKAS patch released on 2002/11/11)

> After preprocessing the process.c file, I found that
> `struct ptrace_faultinfo' and `struct ptrace_ldt' were first defined
> in file `/usr/include/asm/ptrace.h' and then in
> `arch/um/include/skas_ptrace.h'.
> Since `/usr/include/asm/' is a symlink
> in  `/usr/src/linux/` which in turn points to my kernel source,

Making /usr/include/asm a symlink into kernel sources is a very bad thing; if 
your distro did this it's not your fault, but recent distros don't do this 
from ages (neither RedHat nor Mandrake, at least, for what I saw).

>
> This is *exactly* the same content as `arch/um/include/skas_ptrace.h'.
> From what I googled, it seems to be a known bug.  But it think it would
> not be very difficult to make some #define protection around theses
> structures to prevent from changing the destination of `/usr/src/linux/'
> to a source without the SKAS patch applied.

Yes, it wouldn't not hard.
But you should not use the same source tree to apply both patches. I think 
this is explained very clearly and that the patches are not meant to be 
compatible. Also, in that way you easily get into problems because 
include/asm points to asm-i386 and is not updated to point to asm-um.

Also, if you make /usr/include/asm (this holds also for /usr/include/linux) a 
symlink into kernel sources, that is not good.

And I don't think that any update to the host patch will ever be made 
available, since Jeff Dike is making ready the SKAS 4 patch.

-- 
cat <<EOSIGN
Paolo Giarrusso, aka Blaisorblade
Linux Kernel 2.4.21/2.6.0-test on an i686; Linux registered user n. 292729
EOSIGN



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Re: [uml-devel] UML + skas

[Jeff Dike]

le-hen_j@epita.fr said:
> But it think it would not be very difficult to make some #define
> protection around theses structures to prevent from changing the
> destination of `/usr/src/linux/' to a source without the SKAS patch
> applied.

Maybe, but skas4 doesn't have this problem, and /usr/include/asm should
point to the distro kernel headers, not whatever you have sitting in 
/usr/src/linux (and if the distro put a kernel tree there, you should be
building stuff somewhere else).

Of course, this is wrong if there are distros shipping a kernel tree with
the skas patch in it (which maybe SuSE is).  In this case, some sort of
protection would be the right thing for skas3.

				Jeff



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Re: [uml-devel] UML + skas

[attriel]

> Maybe, but skas4 doesn't have this problem, and /usr/include/asm should

Is SKAS4 nearing completion, btw?  I know you said a while ago that you
were working out a last little bug or something, just curious how it's
going :)

--attriel


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Re: [uml-devel] UML + skas

[jeremie le-hen]

> le-hen_j@epita.fr said:
> > But it think it would not be very difficult to make some #define
> > protection around theses structures to prevent from changing the
> > destination of `/usr/src/linux/' to a source without the SKAS patch
> > applied.
> 
> Maybe, but skas4 doesn't have this problem, and /usr/include/asm should
> point to the distro kernel headers, not whatever you have sitting in 
> /usr/src/linux (and if the distro put a kernel tree there, you should be
> building stuff somewhere else).

Ok, I understand better now.  Altough it's a bit off-topic here, I would
like to know where I can understand these subtleties.  Instinctively, I
would say that /usr/include/{asm,linux}/ need to point to the current
kernel headers in order to use an API in sync with the running kernel :
for example, imagine a kernel patch which adds the incoming and outgoing
interfaces in the tuple used by connection tracking in the NetFilter
framework ; /usr/src/linux/include/linux/netfilter_ipv4/ip_conntrack_tuple.h
would be modified, and so applications including
<linux/netfilter_ipv4/ip_conntrack_tuple.h> for any reason would not
use the correct structure.
I must be missing something, but I can't get what.  Please tell me.

Thanks in advance,
-- 
Jeremie LE HEN aka TtZ/TataZ                          jeremie.le-hen@epita.fr
                                                                 ttz@epita.fr
Hi! I'm a .signature virus! Copy me into your ~/.signature to help me spread!


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