[Lguest] Kprobes module makes lguest crash when inserted

[Alexandre Courbot]

Hello everyone,

I'm just playing around with lguest that I just discovered. I hope to
use it for testing/debugging a kernel module of mine instead of
crashing my workstation every time I break something. I considered UML
at first, but my module uses kprobes, which has no support for UML.

Well, maybe there is something wrong about using kprobes within lguest
too (although nothing would suggest that to me - but I'm not a kernel
expert), but every time I insert my module (just plain insmod
mymodule.ko) from the guest, it crashes very badly with a huge pile of
messages. Here is the end (cannot log everything, the list of error
messages is too long for my console buffer):

[   37.554243]  [<c0325a92>] error_code+0x72/0x80
[   37.556341]  [<c012dd30>] do_exit+0x0/0x820
[   37.556359]  [<c0106059>] die+0x289/0x290
[   37.556376]  [<c0325fe0>] do_general_protection+0x0/0x250
[   37.556397]  [<c0325a92>] error_code+0x72/0x80
[   37.556415]  [<c012dd30>] do_exit+0x0/0x820
[   37.556432]  [<c0106059>] die+0x289/0x290
[   37.556450]  [<c0325fe0>] do_general_protection+0x0/0x250
[   37.556471]  [<c0325a92>] error_code+0x72/0x80
[   37.556489]  [<c012dd30>] do_exit+0x0/0x820
[   37.556506]  [<c0106059>] die+0x289/0x290
[   37.556523]  [<c0325fe0>] do_general_protection+0x0/0x250
[   37.556545]  [<c0325a92>] error_code+0x72/0x80
[   37.556562]  [<c032007b>] __vcc_walk+0xab/0xd0
[   37.556580]  [<c012dd30>] do_exit+0x0/0x820
[   37.556597]  [<c0106059>] die+0x289/0x290
[   37.556614]  [<c0325fe0>] do_general_protection+0x0/0x250
[   37.556635]  [<c0325a92>] error_code+0x72/0x80
[   37.556653]  [<c012dd30>] do_exit+0x0/0x820
[   37.556670]  [<c0106059>] die+0x289/0x290
[   37.556687]  [<c0325fe0>] do_general_protection+0x0/0x250
[   37.556709]  [<c0325a92>] error_code+0x72/0x80
[   37.556726]  [<c017007b>] blk_queue_bounce+0x20b/0x260
[   37.556744]  [<c01700d8>] bounce_end_io+0x8/0x90
[   37.556762]  [<c017b800>] sys_write+0x0/0x70
[   37.556779]  [<c0104382>] syscall_call+0x7/0xb
[   37.556797]  [<c0320000>] __vcc_walk+0x30/0xd0
[   37.556818] BUG: unable to handle kernel paging request at virtual
address 37363535
[   37.556843]  printing eip:
[   37.556852] c0105972
[   37.556860] *pde = 00000000
[   37.556869] Recursive die() failure, output suppressed
[   37.556888] Kernel panic - not syncing: Fatal exception in interrupt
lguest: CRASH: Fatal exception in interrupt

This has been performed on 2.6.23-rc5.

To me nothing would suggest that kprobes could not be used with
lguest, but there again I don't know enough about them to pretend
anything. That's why I wanted to submit this issue to you, in case
this is not an expectable behavior.

I'd also glad to hear explanations about this issue, if any.

Thanks,
Alex.