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Date: Sat, 6 Aug 2011 09:15:45 -0400
From: Andrew Lutomirski <luto@....edu>
To: Tejun Heo <tj@...nel.org>
Cc: Matt Helsley <matthltc@...ibm.com>,
Pavel Emelyanov <xemul@...allels.com>,
Nathan Lynch <ntl@...ox.com>,
Oren Laadan <orenl@...columbia.edu>,
Daniel Lezcano <dlezcano@...ibm.com>, S@....edu,
"James E.J. Bottomley" <JBottomley@...allels.com>,
"David S. Miller" <davem@...emloft.net>,
linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [EXAMPLE CODE] Parasite thread injection and TCP connection hijacking
On Sat, Aug 6, 2011 at 9:00 AM, Tejun Heo <tj@...nel.org> wrote:
> Hello,
>
> On Sat, Aug 06, 2011 at 08:45:28AM -0400, Andy Lutomirski wrote:
>> > 2. Decide where to inject the foreign code and save the original code
>> > with PTRACE_PEEKDATA. Tracer can poke any mapped area regardless
>> > of protection flags but it can't add execution permission to the
>> > code, so it needs to choose memory area which already has X flag
>> > set. The example code uses the page the %rip is in.
>>
>> If the process is executing from the vsyscall page, then you'll
>> probably fail. (Admittedly, this is rather unlikely, given that the
>> vsyscalls are now exactly one instruction.) Presumably you also
>> fail if executing from a read-only MAP_SHARED mapping.
>
> Heh, yeah, I originally thought about scanning /proc/PID/maps to look
> for the page to use but was lazy and just used %rip. I think that
> should work. I'll note the problem in README.
>
>> Windows has a facility to more-or-less call mmap on behalf of
>> another process, and another one to directly inject a thread into a
>> remote process. It's traditional to use them for this type of
>> manipulation. Perhaps Linux should get the same thing. (Although
>> you could accomplish much the same thing if you could create a task
>> with your mm but the tracee's fs.)
>
> Actually, the only thing we need on x86_64 is two bytes for the
> syscall instruction because all params are passed through registers
> anyway. We can just set up parameters for mmap, turn on single step,
> point %rip to syscall in the vsyscall page. So, either way, I don't
> think this would be too difficult to solve.
Not any more -- that syscall instruction is gone as of 3.1. You could
search through the vdso to find a syscall, but that seems fragile.
Why not just add a ptrace command to issue a syscall?
--Andy
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