Xen devel - Sep 2007 - Xen Kernel Debug Tools

Greetings,

 

I''m attempting to mash grsecurity-2.1.9 into Xen 3.1.1-rc1.  Last time
I
did this, for Xen 3.02, things went off without much of a hitch.
However, this time I''m running into a snag in the Dom0 kernel when a
para-virtualized  DomU starts up.   The  page fault I''m seeing in the
Xen''s dmesg (xm dmesg) is below, but as it is, its not very helpful.   

 

I''m looking for a Xen tutorial that lists the tools and techniques I
need to debug kernel code, and hopefully associate this stack trace with
a source file and line number.  Does anyone know if such a tutorial
exists?  If so, can you please point me in the right direction?  I''ve
found some dated documents about kdb patches being necessary or some
sort of thing.  I was hoping it would be as easy as turning on debug
support, getting a crash dump, and running it through gdb, but it
doesn''t look like that is the case.

 

 

Here is the page fault exception I''m getting in xm dmesg.  The Dom0
Linux kernel''s dmesg gets no messages.  This happens when I attempt to
start a grsecurity enabled DomU on a grsecurity enabled Dom0.   Starting
a grsecurity enabled DomU on a non-grsecurity Dom0 works just fine.

 

(XEN) Unhandled page fault in domain 14 on VCPU 0 (ec=0010)

(XEN) Pagetable walk from ffffffff80200000:

(XEN)  L4[0x1ff] = 0000000000000000 ffffffffffffffff

(XEN) domain_crash_sync called from entry.S

(XEN) Domain 14 (vcpu#0) crashed on cpu#0:

(XEN) ----[ Xen-3.1.0  x86_64  debug=n  Not tainted ]----

(XEN) CPU:    0

(XEN) RIP:    e033:[<ffffffff80200000>]

(XEN) RFLAGS: 0000000000010202   CONTEXT: guest

(XEN) rax: 0000000000000000   rbx: 0000000000000000   rcx:
0000000000000000

(XEN) rdx: 0000000000000000   rsi: ffffffff80569000   rdi:
0000000000000000

(XEN) rbp: 0000000000000000   rsp: ffffffff80574000   r8:
0000000000000000

(XEN) r9:  0000000000000000   r10: 0000000000000000   r11:
0000000000000000

(XEN) r12: 0000000000000000   r13: 0000000000000000   r14:
0000000000000000

(XEN) r15: 0000000000000000   cr0: 000000008005003b   cr4:
00000000000006f0

(XEN) cr3: 000000041c62a000   cr2: ffffffff80200000

(XEN) ds: 0000   es: 0000   fs: 0000   gs: 0000   ss: e02b   cs: e033

(XEN) Guest stack trace from rsp=ffffffff80574000:

(XEN)   Stack empty.

 

 

Thanks,

 

John Anderson



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> Here is the page fault exception I''m getting in xm dmesg.  The
Dom0
> Linux kernel''s dmesg gets no messages.  This happens when I
attempt to
> start a grsecurity enabled DomU on a grsecurity enabled Dom0.
> Starting a grsecurity enabled DomU on a non-grsecurity Dom0 works just
> fine.
This is pretty surprising. When a domU is actually running, dom0 isn''t
really involved (other than for IO), so its surprising grsec makes a
difference.

Do you get any console output from the guest before it crashes? I''m
wandering if its actually been built incorrectly by the domain builder
running in dom0.

It''s looks like its dieing trying to do an instruction fetch from
ffffffff80200000 which is presumably the page fault handler. 

Are you using a debug build of Xen? You may get some more helpful
output.

Ian

 
> 
> 
> (XEN) Unhandled page fault in domain 14 on VCPU 0 (ec=0010)
> 
> (XEN) Pagetable walk from ffffffff80200000:
> 
> (XEN)  L4[0x1ff] = 0000000000000000 ffffffffffffffff
> 
> (XEN) domain_crash_sync called from entry.S
> 
> (XEN) Domain 14 (vcpu#0) crashed on cpu#0:
> 
> (XEN) ----[ Xen-3.1.0  x86_64  debug=n  Not tainted ]----
> 
> (XEN) CPU:    0
> 
> (XEN) RIP:    e033:[<ffffffff80200000>]
> 
> (XEN) RFLAGS: 0000000000010202   CONTEXT: guest
> 
> (XEN) rax: 0000000000000000   rbx: 0000000000000000   rcx:
> 0000000000000000
> 
> (XEN) rdx: 0000000000000000   rsi: ffffffff80569000   rdi:
> 0000000000000000
> 
> (XEN) rbp: 0000000000000000   rsp: ffffffff80574000   r8:
> 0000000000000000
> 
> (XEN) r9:  0000000000000000   r10: 0000000000000000   r11:
> 0000000000000000
> 
> (XEN) r12: 0000000000000000   r13: 0000000000000000   r14:
> 0000000000000000
> 
> (XEN) r15: 0000000000000000   cr0: 000000008005003b   cr4:
> 00000000000006f0
> 
> (XEN) cr3: 000000041c62a000   cr2: ffffffff80200000
> 
> (XEN) ds: 0000   es: 0000   fs: 0000   gs: 0000   ss: e02b   cs: e033
> 
> (XEN) Guest stack trace from rsp=ffffffff80574000:
> 
> (XEN)   Stack empty.
> 
> 
> 
> 
> 
> Thanks,
> 
> 
> 
> John Anderson

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