Re: [Qemu-devel] [PATCH v2] seccomp: add cacheflush to whitelist

[Andrew Jones]

On Mon, Nov 02, 2015 at 08:37:15PM +0000, Peter Maydell wrote:
> On 2 November 2015 at 19:04, Andrew Jones <address@hidden> wrote:
> > On Mon, Nov 02, 2015 at 06:09:41PM +0000, Peter Maydell wrote:
> >> On 2 November 2015 at 17:56, Andrew Jones <address@hidden> wrote:
> >> > cacheflush is an arm-specific syscall that qemu built for arm
> >> > uses. Add it to the whitelist, but only if we're linking with
> >> > a recent enough libseccomp.
> >> >
> >> > Signed-off-by: Andrew Jones <address@hidden>
> >> > ---
> >> > v2: only add cacheflush if libseccomp supports it
> >> >
> >> >  qemu-seccomp.c | 9 ++++++++-
> >> >  1 file changed, 8 insertions(+), 1 deletion(-)
> >> >
> >> > diff --git a/qemu-seccomp.c b/qemu-seccomp.c
> >> > index 80d034a8d5190..e76097e958779 100644
> >> > --- a/qemu-seccomp.c
> >> > +++ b/qemu-seccomp.c
> >> > @@ -16,6 +16,10 @@
> >> >  #include <seccomp.h>
> >> >  #include "sysemu/seccomp.h"
> >> >
> >> > +#if SCMP_VER_MAJOR >= 2 && SCMP_VER_MINOR >= 2 && SCMP_VER_MICRO >= 3
> >> > +#define HAVE_CACHEFLUSH
> >> > +#endif
> >>
> >> This will claim that a hypothetical future version 3.0.0 does not
> >> have cacheflush...
> >
> > Indeed. Sigh... In that case, how about just
> >
> > #if defined(TARGET_ARM) || defined(TARGET_AARCH64)
> >     { SCMP_SYS(cacheflush), 240 },
> > #endif
> 
> You want to be checking based on the host architecture,
> not the target architecture. Also, not doing the check based
> on seccomp version means there's no hint in the code that the
> ifdefs become obsolete if we raise our cross-architecture
> minimum seccomp version requirement in the future, so really
> a version check is better I think.

Right. OK, I'll stop flinging junk and pull a better version
check together.

Thanks,
drew

> 
> thanks
> -- PMM
>