Question about uprobes

[W. Michael Petullo]

>> I am writing some software that monitors a guest VM using virtual-machine
>> introspection and "hijacks" system calls under certain conditions. For
>> example, the program might inject an int3/breakpoint into the guest
>> kernel at the entry point to sys_open. When the breakpoint is hit, the
>> program might set the guest instruction pointer to the address to which
>> sys_open would have itself returned and set register RAX to some desired
>> error-code return value.
>>
>> The problem I am encountering is that for some reason the process is
>> triggering a "uprobe ... failed to handle uretprobe" message from the
>> guest kernel.  I do not yet know enough about uprobes to understand what
>> might be causing this. Is there something in procedures such as sys_open
>> which must execute to prevent the error which causes the kernel to print
>> this message?

>> What vm  hypervisor do you use?

We are using Xen + libvmi.

I have continued to read the kernel sources, and as best as I can
understand it the kernel installs uprobe instrumentation if it detects
a software breakpoint. Our program does not reinject the software
breakpoints it services back into the guest, so I am still trying to
figure out why uprobes seems to get triggered.

-- 
Mike

:wq