Re: [Xen-devel] potentially nasty oops on startup

[Rik van Riel <riel@xxxxxxxxxx>]

On Sun, 5 Dec 2004, Rik van Riel wrote:

> I'm getting the following oops on startup, and I'm not quite
> sure why.  It looks nasty though, with an invalid page being
> mapped into a process, and a strange looking EIP ...
>
> do_wp_page: bogus page at address 00000449
> VM: killing process kmodule
> Unable to handle kernel NULL pointer dereference at virtual address 00000449
OK, figured it out.  It's kmodule, mmaping /dev/mem and
making vm86 calls.  Select fragments from a strace:

geteuid32()                             = 0
open("/dev/zero", O_RDONLY)             = 4
mmap2(0x10000, 65536, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE|MAP_FIXED, 4, 
0) = 0x10000
open("/dev/mem", O_RDWR)                = 5
mmap2(NULL, 1282, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE|MAP_FIXED, 5, 0) 
= 0
mmap2(0xa0000, 393216, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_FIXED, 5, 0xa0) = 
0xa0000
iopl(0x3)                               = 0
ioperm(0, 0x400, 0x1)                   = 0
rt_sigprocmask(SIG_SETMASK, ~[RTMIN RT_1], [], 8) = 0
vm86old(0x806b48c)                      = -1 ENOSYS (Function not implemented)
rt_sigprocmask(SIG_SETMASK, ~[RTMIN RT_1], [], 8) = 0
vm86old(0x806b48c)                      = -1 ENOSYS (Function not implemented)
rt_sigprocmask(SIG_SETMASK, ~[RTMIN RT_1], [], 8) = 0
vm86old(0x806b48c)                      = -1 ENOSYS (Function not implemented)
rt_sigprocmask(SIG_SETMASK, ~[RTMIN RT_1], [], 8) = 0
vm86old(0x806b48c)                      = -1 ENOSYS (Function not implemented)
rt_sigprocmask(SIG_SETMASK, ~[RTMIN RT_1], [], 8) = 0
vm86old(0x806b48c)                      = -1 ENOSYS (Function not implemented)
rt_sigprocmask(SIG_SETMASK, ~[RTMIN RT_1], [], 8) = 0
vm86old(0x806b48c)                      = -1 ENOSYS (Function not implemented)
rt_sigprocmask(SIG_SETMASK, ~[RTMIN RT_1], [], 8) = 0
vm86old(0x806b48c)                      = -1 ENOSYS (Function not implemented)
rt_sigprocmask(SIG_SETMASK, ~[RTMIN RT_1], [], 8) = 0
vm86old(0x806b48c)                      = -1 ENOSYS (Function not implemented)
rt_sigprocmask(SIG_SETMASK, ~[RTMIN RT_1], [], 8) = 0
vm86old(0x806b48c)                      = -1 ENOSYS (Function not implemented)
rt_sigprocmask(SIG_SETMASK, ~[RTMIN RT_1], [], 8) = 0
vm86old(0x806b48c)                      = -1 ENOSYS (Function not implemented)
rt_sigprocmask(SIG_SETMASK, ~[RTMIN RT_1], [], 8) = 0
vm86old(0x806b48c)                      = -1 ENOSYS (Function not implemented)
rt_sigprocmask(SIG_SETMASK, ~[RTMIN RT_1], [], 8) = 0
vm86old(0x806b48c)                      = -1 ENOSYS (Function not implemented)
rt_sigprocmask(SIG_SETMASK, ~[RTMIN RT_1], [], 8) = 0
vm86old(0x806b48c)                      = -1 ENOSYS (Function not implemented)
rt_sigprocmask(SIG_SETMASK, ~[RTMIN RT_1], [], 8) = 0
vm86old(0x806b48c)                      = -1 ENOSYS (Function not implemented)
rt_sigprocmask(SIG_SETMASK, ~[RTMIN RT_1], [], 8) = 0
vm86old(0x806b48c <unfinished ...>
+++ killed by SIGSEGV +++

Can't say I blame Xen for this.  Yuck.


--
"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are,
by definition, not smart enough to debug it." - Brian W. Kernighan


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