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

[Blue Swirl <blauwirbel@gmail.com>]

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?

> +    { SCMP_SYS(listen), 245 },
> +    { SCMP_SYS(ioctl), 245 },
> +    { SCMP_SYS(eventfd), 245 },
> +    { SCMP_SYS(rt_sigprocmask), 245 },
> +    { SCMP_SYS(write), 244 },
> +    { SCMP_SYS(fcntl), 243 },
> +    { SCMP_SYS(tgkill), 242 },
> +    { SCMP_SYS(rt_sigaction), 242 },
> +    { SCMP_SYS(pipe2), 242 },
> +    { SCMP_SYS(munmap), 242 },
> +    { SCMP_SYS(mremap), 242 },
> +    { SCMP_SYS(getsockname), 242 },
> +    { SCMP_SYS(getpeername), 242 },
> +    { SCMP_SYS(fdatasync), 242 },
> +    { SCMP_SYS(close), 242 }
> +};
> +
> +#define seccomp_whitelist_count ARRAY_SIZE(seccomp_whitelist)

I'm not sure the #define helps much.

> +
> +int seccomp_start(void)
> +{
> +    int rc = 0;
> +    unsigned int i = 0;
> +
> +    rc = seccomp_init(SCMP_ACT_KILL);
> +    if (rc < 0) {
> +        goto seccomp_return;
> +    }
> +
> +    for (i = 0; i < seccomp_whitelist_count; i++) {
> +        rc = seccomp_rule_add(SCMP_ACT_ALLOW, seccomp_whitelist[i].num, 0);
> +        if (rc < 0) {
> +            goto seccomp_return;
> +        }
> +        rc = seccomp_syscall_priority(seccomp_whitelist[i].num,
> +                                      seccomp_whitelist[i].priority);
> +        if (rc < 0) {
> +            goto seccomp_return;
> +        }
> +    }
> +
> +    rc = seccomp_load();
> +
> +  seccomp_return:
> +    seccomp_release();
> +    if (rc < 0) {
> +        fprintf(stderr,
> +                "ERROR: failed to configure the seccomp syscall filter in the kernel\n");

Should this be fatal?

> +    }
> +    return rc;

Return value is not used.

> +}
> diff --git a/qemu-seccomp.h b/qemu-seccomp.h
> new file mode 100644
> index 0000000..3bbdd87
> --- /dev/null
> +++ b/qemu-seccomp.h
> @@ -0,0 +1,9 @@

Usual header protection #ifndeffery missing.

> +#include <seccomp.h>
> +#include "osdep.h"
> +
> +struct QemuSeccompSyscall {
> +    int32_t num;
> +    uint8_t priority;
> +};

This definition is not used elsewhere, so it should be internal to
qemu-seccomp.c.

> +
> +int seccomp_start(void);
> diff --git a/vl.c b/vl.c
> index 204d85b..315afaf 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -61,6 +61,9 @@
>
>  #include <linux/ppdev.h>
>  #include <linux/parport.h>
> +#ifdef CONFIG_LIBSECCOMP
> +#include "qemu-seccomp.h"
> +#endif
>  #endif
>  #ifdef __sun__
>  #include <sys/stat.h>
> @@ -2296,6 +2299,10 @@ int main(int argc, char **argv, char **envp)
>     const char *trace_events = NULL;
>     const char *trace_file = NULL;
>
> +#ifdef CONFIG_LIBSECCOMP
> +    seccomp_start();
> +#endif
> +
>     atexit(qemu_run_exit_notifiers);
>     error_set_progname(argv[0]);
>
> --
> 1.7.9.5
>
>