[uml-devel] 2.6.15-rc2

[uml-devel] 2.6.15-rc2

[Michael Richardson]

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Hash: SHA1


Running a kernel which is not 2.6.15-rc2 (but a couple of merges back,
looking for a place where it works), I get:


Initializing software serial port version 1
Failed to open 'root_fs', errno = 2
RAMDISK: cramfs filesystem found at block 0
RAMDISK: Loading 1228KiB [1 disk] into ram disk... done.
VFS: Mounted root (cramfs filesystem) readonly.
Stub registers -
        0 - bffff000
        1 - 1000
        2 - 3
        3 - 11
        4 - 3
        5 - 0
        6 - bffff000
        7 - 7b
        8 - 7b
        9 - 0
        10 - 0
        11 - ffffffff
        12 - bfffe092
        13 - 73
        14 - 10246
        15 - bffff7fc
        16 - 7b
Kernel panic - not syncing: copy_context_skas0 : failed to wait for SIGUSR1/SIGTRAP, pid = 5136, n = 5136, errno = 0, status = 0xb7f

If I try with "mode=tt", (vs skas0) it boots, but on shutdown, I get:

EIP: 0073:[<40101e18>] CPU: 0 Not tainted ESP: 007b:bf8cec8c EFLAGS: 00000246
    Not tainted
EAX: ffffffda EBX: 40189880 ECX: ffffffff EDX: 00000000
ESI: bf8ced38 EDI: 00000000 EBP: bf8cec98 DS: 007b ES: 007b
a09ff800:  [<a00395bf>] show_regs+0x1cf/0x1e0
a09ff828:  [<a001d25c>] panic_exit+0x2c/0x50
a09ff838:  [<a00506cd>] notifier_call_chain+0x2d/0x50
a09ff858:  [<a003d922>] panic+0x72/0x110
a09ff874:  [<a0022d1e>] wait_stub_done+0xfe/0x180
a09ff8f4:  [<a0023792>] copy_context_skas0+0x1c2/0x270
a09ff9d4:  [<a0022aac>] init_new_context_skas+0x11c/0x1b0
a09ffa08:  [<a003bf97>] copy_mm+0x367/0x3a0
a09ffa50:  [<a003c969>] copy_process+0x499/0xe60
a09ffb40:  [<a003d39e>] do_fork+0x6e/0x1ca
a09ffbac:  [<a001a33b>] sys_fork+0x8b/0xb0
a09ffbe0:  [<a0024512>] handle_syscall+0x112/0x140
a09ffc5c:  [<a0022ed1>] handle_trap+0x31/0x140
a09ffc84:  [<a002357a>] userspace+0x1da/0x230
a09ffce0:  [<a0023f35>] new_thread_handler+0xe5/0x120
a09ffd20:  [<a01cb468>] __restore+0x0/0x8


- -- 
]       ON HUMILITY: to err is human. To moo, bovine.           |  firewalls  [
]   Michael Richardson,    Xelerance Corporation, Ottawa, ON    |net architect[
] mcr@xelerance.com      http://www.sandelman.ottawa.on.ca/mcr/ |device driver[
] panic("Just another Debian GNU/Linux using, kernel hacking, security guy"); [
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Re: [uml-devel] 2.6.15-rc2

[Rob Landley]

On Tuesday 29 November 2005 22:20, Michael Richardson wrote:
> Running a kernel which is not 2.6.15-rc2 (but a couple of merges back,
> looking for a place where it works), I get:

This broke for me too.  The fix went into -rc3.

Rob
-- 
Steve Ballmer: Innovation!  Inigo Montoya: You keep using that word.
I do not think it means what you think it means.


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Re: [uml-devel] 2.6.15-rc2

[Michael Richardson]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1


What was the fix?
Are you using a cramfs initrd?

I built against the v2.6.15-rc3 tag in GIT, and I saw the same failure.
I'm going to make clean again (the rm -rf way) and try again to be
sure...

- -- 
]       ON HUMILITY: to err is human. To moo, bovine.           |  firewalls  [
]   Michael Richardson,    Xelerance Corporation, Ottawa, ON    |net architect[
] mcr@xelerance.com      http://www.sandelman.ottawa.on.ca/mcr/ |device driver[
] panic("Just another Debian GNU/Linux using, kernel hacking, security guy"); [
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Re: [uml-devel] 2.6.15-rc2

[Rob Landley]

On Wednesday 30 November 2005 10:34, Michael Richardson wrote:
> What was the fix?

A quick check through the past few pages of:
http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=shortlog

Finds these four commits:
http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=aa1a64ee12ae130706f3fc0007841ce9b0ddf9c2
http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=17d469715c6453e4994e6617e8f644bf10f38584
http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=e23181deec0d2a8be576faf9d71211abb84d5ccc
http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=39d730ab87f07592e3a3794353f097d5184cae7a

Click "commitdiff" and then right click on "plain" and save as.

> Are you using a cramfs initrd?

Nope.  Squashfs.  (Last time I tried cramfs it had some _serious_ size 
limitations.)

And for testing, I just go:

./linux rootfstype=hostfs rw init=/bin/sh

No special setup required at all, just borrow the host system's root 
directory.  (You probably want to "mount -t proc /proc /proc" and "mount -t 
tmpfs /dev/shm", and "mount -t devpts /dev/pts" before doing anything _too_ 
fancy.)

Getting ctrl-C to work took a bit of doing, but I posted a oneit.c file I made 
that does it, a while back...

> I built against the v2.6.15-rc3 tag in GIT, and I saw the same failure.
> I'm going to make clean again (the rm -rf way) and try again to be
> sure...

Yeah, neither make ARCH=um clean nor make ARCH=um distclean seem to actually 
delete all the files a UML build makes.  I may do something about that one of 
these days...

Rob
-- 
Steve Ballmer: Innovation!  Inigo Montoya: You keep using that word.
I do not think it means what you think it means.


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[uml-devel] Re: 2.6.15-rc2

[Michael Richardson]

[-- Attachment #1: Type: text/plain, Size: 9074 bytes --]


okay, I don't quite understand, but it seemds that -rc2 is okay, but -rc3 is
failing. (-rc2 was failing as far as I could tell on Monday. Maybe I wasn't
running the kernel I thought I was).

Using git bisect, I've reduced the problem to:
          
          39d730ab87f07592e3a3794353f097d5184cae7a is first bad commit
          diff-tree 39d730ab87f07592e3a3794353f097d5184cae7a (from 18317ab0ca5ac0c654be3eac31ebb781b4a5e9b2)
          Author: Jeff Dike <jdike@addtoit.com>
          Date:   Mon Nov 21 21:32:04 2005 -0800

              [PATCH] uml: eliminate use of local in clone stub
                  
    We have a bug in the i386 stub_syscall6 which pushes ebp before the system
    call and pops it afterwards.  Because we use syscall6 to remap the stack, the
    old contents of the stack (and the former value of ebp) are no longer
    available.  Some versions of gcc make from a real local, accessed through ebp,
    despite my efforts to make it obvious that references to from are really
    constants.  This patch attempts to make it even more obvious by eliminating
    from and using a macro to access the stub's data explicitly with constants.
    
    My original thinking on this was to replace syscall6 with a remap_stack
    interface which saved ebp someplace and restored it afterwards.  The problem
    is that there are no registers to put it in, except for esp.  That could work,
    since we can store a constant in esp after the mmap because we just replaced
    the stack.  However, this approach seems a tad cleaner.
    
    Signed-off-by: Jeff Dike <jdike@addtoit.com>
    Signed-off-by: Andrew Morton <akpm@osdl.org>
    Signed-off-by: Linus Torvalds <torvalds@osdl.org>


=== Sigh. I know that this was an annoying fix.

The fault that I get:

RAMDISK: cramfs filesystem found at block 0
RAMDISK: Loading 1228KiB [1 disk] into ram disk... done.
VFS: Mounted root (cramfs filesystem) readonly.
Stub registers -
        0 - bffff000
        1 - 1000
        2 - 3
        3 - 11
        4 - 3
        5 - 0
        6 - bffff000
        7 - 7b
        8 - 7b
        9 - 0
        10 - 0
        11 - ffffffff
        12 - bfffe092
        13 - 73
        14 - 10246
        15 - bffff7fc
        16 - 7b
Kernel panic - not syncing: copy_context_skas0 : failed to wait for SIGUSR1/SIGTRAP, pid = 32345, n = 32345, errno = 0, status = 0xb7f

(copy of initrd at: http://www.sandelman.ottawa.on.ca/tmp/initrd.uml .
umlroot= is interpreted by it as a hostfs to mount after mounting tmpfs on
/dev) 

marajade-[/mara6/openswan/openswan.git] mcr 1070 %gdb /mara1/git/uml-2.6.15/O/um-01/linux
GNU gdb 6.3-debian
...

(gdb) set args initrd=/mara6/sandboxes/openswan.git/UMLPOOL/initrd.uml umlroot=/mara6/sandboxes/openswan.git/UMLPOOL/east/root root=/dev/root rw ssl=pty umid=east
(gdb) run

(gdb) c
Continuing.

Program received signal SIGUSR1, User defined signal 1.
0xa018c031 in kill () at swab.h:134

(gdb) handle SIGUSR1 nostop noprint
Signal        Stop      Print   Pass to program Description
SIGUSR1       No        No      Yes             User defined signal 1
(gdb) c
Continuing

Program received signal SIGSEGV, Segmentation fault.
zlib_inflateInit2_ (z=0xa0309360, w=15, 
    version=0xa280005c <Address 0xa280005c out of bounds>, stream_size=48)
    at /mara1/git/uml-2.6.15/lib/zlib_inflate/inflate.c:57
57        z->state->blocks = NULL;
(gdb) bt
#0  zlib_inflateInit2_ (z=0xa0309360, w=15, 
    version=0xa280005c <Address 0xa280005c out of bounds>, stream_size=48)
    at /mara1/git/uml-2.6.15/lib/zlib_inflate/inflate.c:57
#1  0xa00ec858 in zlib_inflateInit_ (z=0xa280005c, 
    version=0xa280005c <Address 0xa280005c out of bounds>, 
    stream_size=-1568669604)
    at /mara1/git/uml-2.6.15/lib/zlib_inflate/inflate.c:109
#2  0xa00cb122 in cramfs_uncompress_init ()
    at /mara1/git/uml-2.6.15/fs/cramfs/uncompress.c:66
#3  0xa000e07b in init_cramfs_fs ()
    at /mara1/git/uml-2.6.15/fs/cramfs/inode.c:548
#4  0xa000170b in do_initcalls () at /mara1/git/uml-2.6.15/init/main.c:578
#5  0xa00017d1 in do_basic_setup () at /mara1/git/uml-2.6.15/init/main.c:620
#6  0xa0014221 in init (unused=0x0) at /mara1/git/uml-2.6.15/init/main.c:693
#7  0xa0031c49 in run_kernel_thread (fn=0xa00141e0 <init>, arg=0x0, 
    jmp_ptr=0xa280005c) at /mara1/git/uml-2.6.15/arch/um/os-Linux/process.c:216
#8  0xa0022ed3 in new_thread_handler (sig=10) at thread_info.h:47
#9  <signal handler called>
#10 0xa018c031 in kill () at swab.h:134
#11 0x00000000 in ?? ()
#12 0x00000000 in ?? ()
#13 0x00000000 in ?? ()
#14 0x00000000 in ?? ()
#15 0xa021b574 in init_thread_union ()
#16 0xa021cf2c in init_task ()
#17 0xa09caaf8 in ?? ()
#18 0xa021b6c0 in init_thread_union ()
#19 0xa00229e0 in new_thread (stack=0xa021cf2c, switch_buf_ptr=0x0, 
    fork_buf_ptr=0x0, handler=0xa00229e0 <new_thread+96>)
    at /mara1/git/uml-2.6.15/arch/um/kernel/skas/process.c:454

gcc version 3.3.5 (Debian 1:3.3.5-13)

%objdump --disassemble -S O/um-01/arch/um/kernel/skas/clone.o >|clone.S
O/um-01/arch/um/kernel/skas/clone.o:     file format elf32-i386

Disassembly of section .__syscall_stub:

00000000 <stub_clone_handler>:
#define STUB_DATA(field) (((struct stub_data *) UML_CONFIG_STUB_DATA)->field)

void __attribute__ ((__section__ (".__syscall_stub")))
stub_clone_handler(void)
{
   0:	55                   	push   %ebp
   1:	ba 78 00 00 00       	mov    $0x78,%edx
   6:	89 e5                	mov    %esp,%ebp
   8:	b9 fc f7 ff bf       	mov    $0xbffff7fc,%ecx
   d:	89 d0                	mov    %edx,%eax
   f:	83 ec 18             	sub    $0x18,%esp
  12:	89 5d f4             	mov    %ebx,0xfffffff4(%ebp)
  15:	bb 11 84 00 00       	mov    $0x8411,%ebx
  1a:	89 75 f8             	mov    %esi,0xfffffff8(%ebp)
  1d:	89 7d fc             	mov    %edi,0xfffffffc(%ebp)
  20:	cd 80                	int    $0x80
  22:	89 45 f0             	mov    %eax,0xfffffff0(%ebp)
	long err;

	err = stub_syscall2(__NR_clone, CLONE_PARENT | CLONE_FILES | SIGCHLD,
			    UML_CONFIG_STUB_DATA + PAGE_SIZE / 2 -
			    sizeof(void *));
	if(err != 0)
  25:	85 c0                	test   %eax,%eax
  27:	75 6c                	jne    95 <stub_clone_handler+0x95>
  29:	8b 5d f0             	mov    0xfffffff0(%ebp),%ebx
  2c:	bf 1a 00 00 00       	mov    $0x1a,%edi
  31:	89 f8                	mov    %edi,%eax
  33:	89 d9                	mov    %ebx,%ecx
  35:	89 da                	mov    %ebx,%edx
  37:	89 de                	mov    %ebx,%esi
  39:	cd 80                	int    $0x80
  3b:	89 45 f0             	mov    %eax,0xfffffff0(%ebp)
		goto out;

	err = stub_syscall4(__NR_ptrace, PTRACE_TRACEME, 0, 0, 0);
	if(err)
  3e:	85 c0                	test   %eax,%eax
  40:	75 53                	jne    95 <stub_clone_handler+0x95>
  42:	be 68 00 00 00       	mov    $0x68,%esi
  47:	bb 01 00 00 00       	mov    $0x1,%ebx
  4c:	8b 55 f0             	mov    0xfffffff0(%ebp),%edx
  4f:	b9 08 f0 ff bf       	mov    $0xbffff008,%ecx
  54:	89 f0                	mov    %esi,%eax
  56:	cd 80                	int    $0x80
  58:	89 45 f0             	mov    %eax,0xfffffff0(%ebp)
		goto out;

	err = stub_syscall3(__NR_setitimer, ITIMER_VIRTUAL,
			    (long) &STUB_DATA(timer), 0);
	if(err)
  5b:	85 c0                	test   %eax,%eax
  5d:	75 36                	jne    95 <stub_clone_handler+0x95>
  5f:	8b 35 04 f0 ff bf    	mov    0xbffff004,%esi
  65:	bb 00 f0 ff bf       	mov    $0xbffff000,%ebx
  6a:	b9 00 10 00 00       	mov    $0x1000,%ecx
  6f:	ba 03 00 00 00       	mov    $0x3,%edx
  74:	89 75 ec             	mov    %esi,0xffffffec(%ebp)
  77:	8b 3d 00 f0 ff bf    	mov    0xbffff000,%edi
  7d:	be 11 00 00 00       	mov    $0x11,%esi
  82:	89 f8                	mov    %edi,%eax
  84:	8b 7d ec             	mov    0xffffffec(%ebp),%edi
  87:	55                   	push   %ebp
  88:	89 c5                	mov    %eax,%ebp
  8a:	b8 c0 00 00 00       	mov    $0xc0,%eax
  8f:	cd 80                	int    $0x80
  91:	5d                   	pop    %ebp
  92:	89 45 f0             	mov    %eax,0xfffffff0(%ebp)
		goto out;

	err = stub_syscall6(STUB_MMAP_NR, UML_CONFIG_STUB_DATA, PAGE_SIZE,
			    PROT_READ | PROT_WRITE, MAP_FIXED | MAP_SHARED,
			    STUB_DATA(fd), STUB_DATA(offset));
 out:
	/* save current result. Parent: pid; child: retcode of mmap */
	STUB_DATA(err) = err;
  95:	8b 45 f0             	mov    0xfffffff0(%ebp),%eax
  98:	a3 18 f0 ff bf       	mov    %eax,0xbffff018
  9d:	cc                   	int3   
	trap_myself();
}
  9e:	8b 5d f4             	mov    0xfffffff4(%ebp),%ebx
  a1:	8b 75 f8             	mov    0xfffffff8(%ebp),%esi
  a4:	8b 7d fc             	mov    0xfffffffc(%ebp),%edi
  a7:	89 ec                	mov    %ebp,%esp
  a9:	5d                   	pop    %ebp
  aa:	c3                   	ret    



-- 
]       ON HUMILITY: to err is human. To moo, bovine.           |  firewalls  [
]   Michael Richardson,    Xelerance Corporation, Ottawa, ON    |net architect[
] mcr@xelerance.com      http://www.sandelman.ottawa.on.ca/mcr/ |device driver[
] panic("Just another Debian GNU/Linux using, kernel hacking, security guy"); [

[-- Attachment #2: Type: application/pgp-signature, Size: 480 bytes --]

Re: [uml-devel] Re: 2.6.15-rc2

[Blaisorblade]

On Thursday 01 December 2005 17:03, Michael Richardson wrote:
> okay, I don't quite understand, but it seemds that -rc2 is okay, but -rc3
> is failing. (-rc2 was failing as far as I could tell on Monday. Maybe I
> wasn't running the kernel I thought I was).

> Using git bisect, 

must learn that, yep...

> I've reduced the problem to: 

Yes, this happens due to GCC doing quite the opposite of what the patch should 
do, in the immediately following line. I've experienced this one too.

>           39d730ab87f07592e3a3794353f097d5184cae7a is first bad commit
>           diff-tree 39d730ab87f07592e3a3794353f097d5184cae7a (from

> Stub registers -

>         12 - bfffe092

This is the content of EIP.

> Kernel panic - not syncing: copy_context_skas0 : failed to wait for
> SIGUSR1/SIGTRAP, pid = 32345, n = 32345, errno = 0, status = 0xb7f

Ok - status = stopped for SIGSEGV.

> Program received signal SIGSEGV, Segmentation fault.

This backtrace is quite different from the other one - and checking for 
independent problems with cramfs may be worth... However, let's go back on 
main problem (below).

> zlib_inflateInit2_ (z=0xa0309360, w=15,
>     version=0xa280005c <Address 0xa280005c out of bounds>, stream_size=48)
>     at /mara1/git/uml-2.6.15/lib/zlib_inflate/inflate.c:57
> 57        z->state->blocks = NULL;
> (gdb) bt
> #0  zlib_inflateInit2_ (z=0xa0309360, w=15,
>     version=0xa280005c <Address 0xa280005c out of bounds>, stream_size=48)
>     at /mara1/git/uml-2.6.15/lib/zlib_inflate/inflate.c:57

Ok, here we replace the stack, in the below int 0x80. The old stack contents 
are not copied, and we have random crap on the new stack.

>   8a:	b8 c0 00 00 00       	mov    $0xc0,%eax
>   8f:	cd 80                	int    $0x80
>   91:	5d                   	pop    %ebp

Here we pop an invalid value into ebp - so we need to keep GCC from using %ebp 
afterwards.

This will fail. Notice the "92" - it matches last digits of EIP (the rest can 
change due to relocation, but the last digits are a good ID of the 
instruction).

>   92:	89 45 f0             	mov    %eax,0xfffffff0(%ebp)

%eax is the return value of the syscall. Gcc saves it on the stack and puts it 
back on %eax, but only with the patch.

>   95:	8b 45 f0             	mov    0xfffffff0(%ebp),%eax

>   98:	a3 18 f0 ff bf       	mov    %eax,0xbffff018

The patch is intended to make sure the _above_ instruction is assembled 
correctly.


>   9d:	cc                   	int3
> 	trap_myself();
> }

The below is ignored thanks to the int3.

-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade

		
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Re: [uml-devel] 2.6.15-rc2

[Blaisorblade]

On Wednesday 30 November 2005 05:20, Michael Richardson wrote:
> Running a kernel which is not 2.6.15-rc2 (but a couple of merges back,
> looking for a place where it works), I get:

> If I try with "mode=tt", (vs skas0) it boots, but on shutdown, I get:

I got it too, and actually I think it's triggerable by playing with proc 
(something like ps with the "l" flag should do, but never tested). I've even 
diagnosed and sent a report to Jeff, we just need to fix it up.

It was introduced in the sysrq-t patch - some macros return 0xdeadbeef when 
SKAS mode is compile-time disabled, and have only a SKAS implementation 
(which is broken for TT mode but is used there too).

Btw, it was not in the first Allan's version that bug, it was introduced 
later.

> EIP: 0073:[<40101e18>] CPU: 0 Not tainted ESP: 007b:bf8cec8c EFLAGS:
> 00000246 Not tainted
> EAX: ffffffda EBX: 40189880 ECX: ffffffff EDX: 00000000
> ESI: bf8ced38 EDI: 00000000 EBP: bf8cec98 DS: 007b ES: 007b
> a09ff800:  [<a00395bf>] show_regs+0x1cf/0x1e0
> a09ff828:  [<a001d25c>] panic_exit+0x2c/0x50
> a09ff838:  [<a00506cd>] notifier_call_chain+0x2d/0x50
> a09ff858:  [<a003d922>] panic+0x72/0x110
> a09ff874:  [<a0022d1e>] wait_stub_done+0xfe/0x180
> a09ff8f4:  [<a0023792>] copy_context_skas0+0x1c2/0x270
> a09ff9d4:  [<a0022aac>] init_new_context_skas+0x11c/0x1b0
> a09ffa08:  [<a003bf97>] copy_mm+0x367/0x3a0
> a09ffa50:  [<a003c969>] copy_process+0x499/0xe60
> a09ffb40:  [<a003d39e>] do_fork+0x6e/0x1ca
> a09ffbac:  [<a001a33b>] sys_fork+0x8b/0xb0
> a09ffbe0:  [<a0024512>] handle_syscall+0x112/0x140
> a09ffc5c:  [<a0022ed1>] handle_trap+0x31/0x140
> a09ffc84:  [<a002357a>] userspace+0x1da/0x230
> a09ffce0:  [<a0023f35>] new_thread_handler+0xe5/0x120
> a09ffd20:  [<a01cb468>] __restore+0x0/0x8

-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade

	

	
		
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