Re: [PATCH V1 24/26] seccomp: cpr-exec blocker

[Steven Sistare]

On 5/10/2024 3:54 AM, Daniel P. Berrangé wrote:
> On Mon, Apr 29, 2024 at 08:55:33AM -0700, Steve Sistare wrote:
> > cpr-exec mode needs permission to exec.  Block it if permission is denied.
> >
> > Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
> > ---
> >   include/sysemu/seccomp.h |  1 +
> >   system/qemu-seccomp.c    | 10 ++++++++--
> >   system/vl.c              |  6 ++++++
> >   3 files changed, 15 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/sysemu/seccomp.h b/include/sysemu/seccomp.h
> > index fe85989..023c0a1 100644
> > --- a/include/sysemu/seccomp.h
> > +++ b/include/sysemu/seccomp.h
> > @@ -22,5 +22,6 @@
> >   #define QEMU_SECCOMP_SET_RESOURCECTL (1 << 4)
> >   
> >   int parse_sandbox(void *opaque, QemuOpts *opts, Error **errp);
> > +uint32_t qemu_seccomp_get_opts(void);
> >   
> >   #endif
> > diff --git a/system/qemu-seccomp.c b/system/qemu-seccomp.c
> > index 5c20ac0..0d2a561 100644
> > --- a/system/qemu-seccomp.c
> > +++ b/system/qemu-seccomp.c
> > @@ -360,12 +360,18 @@ static int seccomp_start(uint32_t seccomp_opts, Error 
> > **errp)
> >       return rc < 0 ? -1 : 0;
> >   }
> >   
> > +static uint32_t seccomp_opts;
> > +
> > +uint32_t qemu_seccomp_get_opts(void)
> > +{
> > +    return seccomp_opts;
> > +}
> > +
> >   int parse_sandbox(void *opaque, QemuOpts *opts, Error **errp)
> >   {
> >       if (qemu_opt_get_bool(opts, "enable", false)) {
> > -        uint32_t seccomp_opts = QEMU_SECCOMP_SET_DEFAULT
> > -                | QEMU_SECCOMP_SET_OBSOLETE;
> >           const char *value = NULL;
> > +        seccomp_opts = QEMU_SECCOMP_SET_DEFAULT | QEMU_SECCOMP_SET_OBSOLETE;
> >   
> >           value = qemu_opt_get(opts, "obsolete");
> >           if (value) {
> > diff --git a/system/vl.c b/system/vl.c
> > index 7252100..b76881e 100644
> > --- a/system/vl.c
> > +++ b/system/vl.c
> > @@ -76,6 +76,7 @@
> >   #include "hw/block/block.h"
> >   #include "hw/i386/x86.h"
> >   #include "hw/i386/pc.h"
> > +#include "migration/blocker.h"
> >   #include "migration/cpr.h"
> >   #include "migration/misc.h"
> >   #include "migration/snapshot.h"
> > @@ -2493,6 +2494,11 @@ static void qemu_process_early_options(void)
> >       QemuOptsList *olist = qemu_find_opts_err("sandbox", NULL);
> >       if (olist) {
> >           qemu_opts_foreach(olist, parse_sandbox, NULL, &error_fatal);
> > +        if (qemu_seccomp_get_opts() & QEMU_SECCOMP_SET_SPAWN) {
> > +            Error *blocker = NULL;
> > +            error_setg(&blocker, "-sandbox denies exec for cpr-exec");
> > +            migrate_add_blocker_mode(&blocker, MIG_MODE_CPR_EXEC, 
> > &error_fatal);
> > +        }
> >       }
> >   #endi
>
> There are a whole pile of features that get blocked wehn -sandbox is
> used. I'm not convinced we should be adding code to check for specific
> blocked features, as such a list will always be incomplete at best, and
> incorrectly block things at worst.
>
> I view this primarily as a documentation task for the cpr-exec command.

For cpr and live migration, we do our best to prevent breaking the guest
for cases we know will fail.  Independently, a clear error message here
will reduce error reports for this new cpr feature.

Would it be more palatable if I move this blocker's creation to cpr_mig_init?

- Steve