[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [PATCH 2/3] xen/livepatch: do Xen build-id check earlier



On Mon, Sep 23, 2024 at 12:04:30PM +0100, Andrew Cooper wrote:
> On 20/09/2024 10:36 am, Roger Pau Monne wrote:
> > The check against the expected Xen build ID should be done ahead of 
> > attempting
> > to apply the alternatives contained in the livepatch.
> >
> > If the CPUID in the alternatives patching data is out of the scope of the
> > running Xen featureset the BUG() in _apply_alternatives() will trigger thus
> > bringing the system down.  Note the layout of struct alt_instr could also
> > change between versions.  It's also possible for struct 
> > exception_table_entry
> > to have changed format, hence possibly leading to other errors.
> >
> > Move the Xen build ID check to be done ahead of any processing of the 
> > livepatch
> > payload sections.
> >
> > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> > ---
> >  xen/common/livepatch.c | 9 +++++----
> >  1 file changed, 5 insertions(+), 4 deletions(-)
> >
> > diff --git a/xen/common/livepatch.c b/xen/common/livepatch.c
> > index cea47ffe4c84..3e4fce036a1c 100644
> > --- a/xen/common/livepatch.c
> > +++ b/xen/common/livepatch.c
> > @@ -767,6 +767,11 @@ static int prepare_payload(struct payload *payload,
> >      if ( rc )
> >          return rc;
> >  
> > +    /* Perform the Xen build-id check ahead of doing any more processing. 
> > */
> > +    rc = xen_build_id_dep(payload);
> > +    if ( rc )
> > +        return rc;
> > +
> 
> While a step in the right direction, I think this needs to be moved far
> earlier.  Even here, it's behind the processing of the livepatch func
> state, which is something that can also change like alt_instr.
> 
> The buildid checks need to be as early as possible.  Looking through the
> logic (which doesn't have great names/splits), I'd say the buildid
> checks want to be between livepatch_elf_load() (which parses the
> structure of the ELF), and move_payload() (which starts copying it into
> place).
> 
> That would involve moving check_special_sections() too, but I think it's
> the right thing to do.

My plan would be to move check_special_sections() ahead and expand its
logic to also check that the expected buildid matches the running
hypervisor one.

Thanks, Roger.



 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.