Re: [Qemu-devel] [PATCHv4 0/4] Sandboxing Qemu guests with Libseccomp

[Blue Swirl]

On Mon, Jul 23, 2012 at 12:59 PM, Eduardo Otubo
<address@hidden> wrote:
> On Tue, Jul 17, 2012 at 04:19:11PM -0300, Eduardo Otubo wrote:
>> Hello all,
>>
>> This patch is an effort to sandbox Qemu guests using Libseccomp[0]. The 
>> patches
>> that follows are pretty simple and straightforward. I added the correct 
>> options
>> and checks to the configure script and the basic calls to libseccomp in the
>> main loop at vl.c. Details of each one are in the emails of the patch set.
>>
>> This support limits the system call footprint of the entire QEMU process to a
>> limited set of syscalls, those that we know QEMU uses. The idea is to limit 
>> the
>> allowable syscalls, therefore limiting the impact that an attacked guest 
>> could
>> have on the host system.
>>
>> It's important to note that the libseccomp itself needs the seccomp mode 2
>> feature in the kernel, which is only available in kernel versions older (or
>> equal) than 3.5-rc1.
>>
>> v2: Files separated in qemu-seccomp.c and qemu-seccomp.h for a cleaner
>>     implementation. The development was tested with the 3.5-rc1 kernel.
>>
>> v3: As we discussed in previous emails in this mailing list, this feature is
>>     not supposed to replace existing security feature, but add another layer 
>> to
>>     the whole. The whitelist should contain all the syscalls QEMU needs. And 
>> as
>>     stated by Will Drewry's commit message[1]: "Filter programs will be 
>> inherited
>>     across fork/clone and execve.", the same white list should be passed 
>> along from
>>     the father process to the child, then execve() shouldn't be a problem. 
>> Note
>>     that there's a feature PR_SET_NO_NEW_PRIVS in seccomp mode 2 in the 
>> kernel,
>>     this prevents processes from gaining privileges on execve. For example, 
>> this
>>     will prevent qemu (if running unprivileged) from executing setuid 
>> programs[2].
>>
>> v4: Introducing "debug" mode on libseccomp support. The "debug" mode will set
>>     the flag SCMP_ACT_TRAP when calling seccomp_start(). It will verbosely
>>     print a message to the stderr in the form "seccomp: illegal system call
>>     execution trapped: XXX" and resume the execution. This is really just 
>> used as
>>     debug mode, it helps users and developers to full fill the whitelist.
>>
>> As always, comments are more than welcome.
>
> Hello folks,
>
> Does anyone got a chance to take a look at these? Thanks in advance :)

The patches look OK as the first step.

I think the next step (1.3?) should be to adjust the code to launch a
couple of threads with different sets of allowed system calls based on
their needs.

>
>>
>> Regards,
>>
>> [0] - http://sourceforge.net/projects/libseccomp/
>> [1] - 
>> http://git.kernel.org/?p=linux/kernel/git/next/linux-next.git;a=commit;h=e2cfabdfd075648216f99c2c03821cf3f47c1727
>> [2] - https://lkml.org/lkml/2012/4/12/457
>>
>> Eduardo Otubo (4):
>>   Adding support for libseccomp in configure and Makefile
>>   Adding qemu-seccomp.[ch]
>>   Adding qemu-seccomp-debug.[ch]
>>   Adding seccomp calls to vl.c
>>
>>  Makefile.objs        |   10 ++++
>>  configure            |   34 ++++++++++++++
>>  qemu-seccomp-debug.c |   95 +++++++++++++++++++++++++++++++++++++
>>  qemu-seccomp-debug.h |   38 +++++++++++++++
>>  qemu-seccomp.c       |  126 
>> ++++++++++++++++++++++++++++++++++++++++++++++++++
>>  qemu-seccomp.h       |   22 +++++++++
>>  vl.c                 |   31 +++++++++++++
>>  7 files changed, 356 insertions(+)
>>  create mode 100644 qemu-seccomp-debug.c
>>  create mode 100644 qemu-seccomp-debug.h
>>  create mode 100644 qemu-seccomp.c
>>  create mode 100644 qemu-seccomp.h
>>
>> --
>> 1.7.9.5
>>
>
> --
> Eduardo Otubo
> Software Engineer
> Linux Technology Center
> IBM Systems & Technology Group
> Mobile: +55 19 8135 0885
> address@hidden
>