On Thu, Sep 26, 2024 at 11:21 AM Roger Pau Monne <[email protected]> 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 leading to other kind of errors if parsing of > the > payload is done ahead of checking if the Xen build-id matches. > > Move the Xen build ID check as early as possible. To do so introduce a new > check_xen_buildid() function that parses and checks the Xen build-id before > moving the payload. Since the expected Xen build-id is used early to > detect whether the livepatch payload could be loaded, there's no reason to > store it in the payload struct, as a non-matching Xen build-id won't get the > payload populated in the first place. > > Note printing the expected Xen build ID has part of dumping the payload > information is no longer done: all loaded payloads would have Xen build IDs > matching the running Xen, otherwise they would have failed to load. > > Fixes: 879615f5db1d ('livepatch: Always check hypervisor build ID upon > livepatch upload') > Signed-off-by: Roger Pau Monné <[email protected]>
Reviewed-by: Ross Lagerwall <[email protected]> Should the ELF_LIVEPATCH_XEN_DEPENDS check also be dropped from check_special_sections() since it is no longer necessary? Ross
