[Virtio-fs] [PATCH] virtiofsd: Add gettimeofday to the seccomp whitelist

[Stefan Hajnoczi]

On Tue, Jul 30, 2019 at 05:50:00PM -0400, Masayoshi Mizuma wrote:
> From: Masayoshi Mizuma <m.mizuma at jp.fujitsu.com>
> 
> When I run fsstress on the virtio filesystem, virtiofsd sometimes
> exits abnormally because it receives SIGSYS.
> 
> >From strace:
>   195852 15:07:47.799331 read(8, "\1\0\0\0\0\0\0\0", 8) = 8 <0.000011>
>   195852 15:07:47.799379 gettimeofday( <unfinished ...>
>   195852 15:07:53.354340 <... gettimeofday resumed> <unfinished ...>) = ?
>   195852 15:07:53.400243 +++ killed by SIGSYS (core dumped) +++
> 
> That is because virtiofsd calls gettimeofday() system call but
> the system call isn't in the seccomp whitelist.
> 
> virtiofsd doesn't call gettimeofday() directly. glib library
> function may call g_get_current_time() and g_get_current_time()
> calls the system call.
> 
> Add gettimeofday() to the seccomp whitelist.
> 
> Signed-off-by: Masayoshi Mizuma <m.mizuma at jp.fujitsu.com>
> ---
>  contrib/virtiofsd/seccomp.c | 1 +
>  1 file changed, 1 insertion(+)

Have you checked that your guest is using the vdso gettimeofday()
implementation?  gettimeofday() is implemented in userspace without a
syscall using vdso to improve performance.  If your guest isn't using it
then performance will be worse.  (There is a fallback code path in the
vdso that invokes the syscall but I'm not sure it is taken in normal
cases.)

The patch is fine though:

Reviewed-by: Stefan Hajnoczi <stefanha at redhat.com>
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