Messages in this thread | | | Subject | Re: [PATCH 0/6] add system vulnerability sysfs entries | From | Jeremy Linton <> | Date | Wed, 12 Dec 2018 09:48:03 -0600 |
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Hi Dave,
Thanks for looking at this!
On 12/13/2018 06:07 AM, Dave Martin wrote: > On Thu, Dec 06, 2018 at 05:44:02PM -0600, Jeremy Linton wrote: >> Part of this series was originally by Mian Yousaf Kaukab. >> >> Arm64 machines should be displaying a human readable >> vulnerability status to speculative execution attacks in >> /sys/devices/system/cpu/vulnerabilities > > Is there any agreement on the strings that will be returned in there? > > A quick search didn't find anything obvious upstream. There is > documentation proposed in [1], but I don't know what happened to it and > it doesn't define the mitigation strings at all. (I didn't follow the > discussion, so there is likely background here I'm not aware of.) > > If the mitigation strings are meaningful at all, they really ought to be > documented somewhere since this is ABI.
I think they are in testing? But that documentation is missing the "Unknown" state which tends to be our default case for "we don't have a complete white/black list", or "mitigation disabled, we don't know if your vulnerable", etc.
I'm not sure I like the "Unknown" state, but we can try to add it to the documentation.
> >> This series enables that behavior by providing the expected >> functions. Those functions expose the cpu errata and feature >> states, as well as whether firmware is responding appropriately >> to display the overall machine status. This means that in a >> heterogeneous machine we will only claim the machine is mitigated >> or safe if we are confident all booted cores are safe or >> mitigated. Otherwise, we will display unknown or unsafe >> depending on how much of the machine configuration can >> be assured. > > Can the vulnerability status change once we enter userspace?
Generally no, for heterogeneous machines I think the answer here is yes, a user could check the state, and have it read "Not affected" then bring another core online which causes the state to change at which point if they re-read /sys it may reflect another state. OTOH, given that we tend to default to mitigated usually this shouldn't be an issue unless someone has disabled the mitigation.
> > I see no locking or other concurrency protections, and various global > variables that could be __ro_after_init if nothing will change them > after boot.
I think the state changes are all protected due to the fact the bringing a core online/offline is serialized.
> > If they can change after boot, userspace has no way to be notified,
Is checking on hotplug notification sufficient?
> > (I haven't grokked the patches fully, so the answer to this question may > be reasonably straightforward...) > > > Cheers > ---Dave > > [1] https://lkml.org/lkml/2018/1/8/145 >
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