Re: [Qemu-devel] [RFC] [PATCHv2 2/2] Adding basic calls to libseccomp in vl.c

From: Blue Swirl <blauwirbel@gmail.com>
To: "Daniel P. Berrange" <berrange@redhat.com>
Cc: qemu-devel@nongnu.org, Eduardo Otubo <otubo@linux.vnet.ibm.com>
Subject: Re: [Qemu-devel] [RFC] [PATCHv2 2/2] Adding basic calls to libseccomp in vl.c
Date: Fri, 15 Jun 2012 19:04:45 +0000	[thread overview]
Message-ID: <CAAu8pHuZgMXUPsaLGrk7sbUWi=2BJJc_-xkrL+wQnZvd9XVjZA@mail.gmail.com> (raw)
In-Reply-To: <20120613203305.GC6019@redhat.com>

On Wed, Jun 13, 2012 at 8:33 PM, Daniel P. Berrange <berrange@redhat.com> wrote:
> On Wed, Jun 13, 2012 at 07:56:06PM +0000, Blue Swirl wrote:
>> On Wed, Jun 13, 2012 at 7:20 PM, Eduardo Otubo <otubo@linux.vnet.ibm.com> wrote:
>> > I added a syscall struct using priority levels as described in the
>> > libseccomp man page. The priority numbers are based to the frequency
>> > they appear in a sample strace from a regular qemu guest run under
>> > libvirt.
>> >
>> > Libseccomp generates linear BPF code to filter system calls, those rules
>> > are read one after another. The priority system places the most common
>> > rules first in order to reduce the overhead when processing them.
>> >
>> > Also, since this is just a first RFC, the whitelist is a little raw. We
>> > might need your help to improve, test and fine tune the set of system
>> > calls.
>> >
>> > v2: Fixed some style issues
>> >        Removed code from vl.c and created qemu-seccomp.[ch]
>> >        Now using ARRAY_SIZE macro
>> >        Added more syscalls without priority/frequency set yet
>> >
>> > Signed-off-by: Eduardo Otubo <otubo@linux.vnet.ibm.com>
>> > ---
>> >  qemu-seccomp.c |   73 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>> >  qemu-seccomp.h |    9 +++++++
>> >  vl.c           |    7 ++++++
>> >  3 files changed, 89 insertions(+)
>> >  create mode 100644 qemu-seccomp.c
>> >  create mode 100644 qemu-seccomp.h
>> >
>> > diff --git a/qemu-seccomp.c b/qemu-seccomp.c
>> > new file mode 100644
>> > index 0000000..048b7ba
>> > --- /dev/null
>> > +++ b/qemu-seccomp.c
>> > @@ -0,0 +1,73 @@
>>
>> Copyright and license info missing.
>>
>> > +#include <stdio.h>
>> > +#include <seccomp.h>
>> > +#include "qemu-seccomp.h"
>> > +
>> > +static struct QemuSeccompSyscall seccomp_whitelist[] = {
>>
>> 'const'
>>
>> > +    { SCMP_SYS(timer_settime), 255 },
>> > +    { SCMP_SYS(timer_gettime), 254 },
>> > +    { SCMP_SYS(futex), 253 },
>> > +    { SCMP_SYS(select), 252 },
>> > +    { SCMP_SYS(recvfrom), 251 },
>> > +    { SCMP_SYS(sendto), 250 },
>> > +    { SCMP_SYS(read), 249 },
>> > +    { SCMP_SYS(brk), 248 },
>> > +    { SCMP_SYS(clone), 247 },
>> > +    { SCMP_SYS(mmap), 247 },
>> > +    { SCMP_SYS(mprotect), 246 },
>> > +    { SCMP_SYS(ioctl), 245 },
>> > +    { SCMP_SYS(recvmsg), 245 },
>> > +    { SCMP_SYS(sendmsg), 245 },
>> > +    { SCMP_SYS(accept), 245 },
>> > +    { SCMP_SYS(connect), 245 },
>> > +    { SCMP_SYS(bind), 245 },
>>
>> It would be nice to avoid connect() and bind(). Perhaps seccomp init
>> should be postponed to after all sockets have been created?
>
> If you want to migrate your guest, you need to be able to
> call connect() at an arbitrary point in the QEMU process'
> lifecycle. So you can't avoid allowing connect(). Similarly
> if you want to allow hotplug of NICs (and their backends)
> then you need to have both bind() + connect() available.

That's bad. Migration could conceivably be extended to use file
descriptor passing, but hotplug is more tricky.

It's probably easier to split QEMU to two processes, one with greater
rights like bind(), connect() etc. and another with tighter set.

>
>
> Daniel
> --
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