On Fri, Jul 17, 2026 at 06:52:46AM -0400, Michael S. Tsirkin wrote: > On Fri, Jul 17, 2026 at 12:46:52PM +0200, Greg Kroah-Hartman wrote: > > On Fri, Jul 17, 2026 at 06:23:57AM -0400, Michael S. Tsirkin wrote: > > > On Fri, Jul 17, 2026 at 12:15:09PM +0200, Greg Kroah-Hartman wrote: > > > > On Fri, Jul 17, 2026 at 06:10:41AM -0400, Michael S. Tsirkin wrote: > > > > > On Fri, Jul 17, 2026 at 11:14:23AM +0200, Greg Kroah-Hartman wrote: > > > > > > On Fri, Jul 17, 2026 at 04:59:32AM -0400, Michael S. Tsirkin wrote: > > > > > > > On Fri, Jul 17, 2026 at 10:39:40AM +0200, David Hildenbrand (Arm) > > > > > > > wrote: > > > > > > > > On 7/17/26 07:48, Michael S. Tsirkin wrote: > > > > > > > > > On Thu, Jul 16, 2026 at 05:59:05PM +0200, David Hildenbrand > > > > > > > > > (Arm) wrote: > > > > > > > > >>> Or do we just always trust virtio mem devices explicitly? > > > > > > > > >> > > > > > > > > >> It's hard for me to understand where we draw the line, > > > > > > > > >> really. > > > > > > > > >> > > > > > > > > >> But maybe MST can clarify what we care about in virtio world > > > > > > > > >> where the > > > > > > > > >> hypervisor is fully in charge of the device, > > > > > > > > > > > > > > > > > > Generally: > > > > > > > > > - The guest is expected to whitelist drivers (most drivers > > > > > > > > > have not > > > > > > > > > been audited). > > > > > > > > > > > > > > > > But even if you audited your driver, who makes sure that we > > > > > > > > consider all ways > > > > > > > > where the device could mess with us? > > > > > > > > > > > > > > A lot of this is up to a correct setup. For example, make sure all > > > > > > > filesystems are encrypted and refuse to mount unencrypted ones. > > > > > > > > > > > > > > > Something feels off here. > > > > > > > > > > > > > > > > Handling selected out-of-spec scenarios like this feels like a > > > > > > > > band-aid. Happy > > > > > > > > to be corrected. > > > > > > > > > > > > > > Well Documentation/security/snp-tdx-threat-model.rst puts it like > > > > > > > this: > > > > > > > It is important to note > > > > > > > that this doesn’t imply that the host or VMM are intentionally > > > > > > > malicious, but that there exists a security value in having a > > > > > > > small CoCo > > > > > > > VM TCB. > > > > > > > > > > > > > > and > > > > > > > > > > > > > > While traditionally the host has unlimited access to guest data > > > > > > > and can > > > > > > > leverage this access to attack the guest, the CoCo systems > > > > > > > mitigate such > > > > > > > attacks by adding security features like guest data > > > > > > > confidentiality and > > > > > > > integrity protection. > > > > > > > > > > > > > > > > > > > > > now, when we are talking about "mitigation" it is indeed becoming > > > > > > > a bit > > > > > > > murky. > > > > > > > > > > > > > > > > > > > > > For me, a rule of thumb I came up with is that if the validation > > > > > > > happens > > > > > > > to also be helful for users e.g. to work around buggy devices, > > > > > > > or maybe because we feel failing gracefully is nice because this > > > > > > > will allow to later make use of this config and old drivers will > > > > > > > fail but at least not panic, then it is good to include. > > > > > > > > > > > > Why not do what USB does? Don't trust the device until AFTER > > > > > > probe() > > > > > > succeeds? All of the needed checking should happen before then, as > > > > > > that > > > > > > is a "slow path" so lots of validation and the like can happen at > > > > > > that > > > > > > point. > > > > > > > > > > > > After that, during the normal data paths, after the driver is bound, > > > > > > trust it all you want as attempting to validate every single packet > > > > > > is > > > > > > just going to be impossible. > > > > > > > > > > > > thanks, > > > > > > > > > > > > greg k-h > > > > > > > > > > People do expect that data path validation at this point. > > > > > > > > Ok, so you want this patch :) > > > > > > > > And more, as you need to treat everything from the host as "untrusted", > > > > and it must be "verified". > > > > > > Well. First it's not me) Second it's only specific configurations - > > > for example there's no short term plan to validate filesystem code, people > > > are expected to rely on encryption. The reasons have more to do > > > with the available manpower than anything else. > > > > Sure, but again, for subsystems, you have to define your threat model as > > the LLMs are churning against the code base and coming up with lots of > > crazy ideas if a device should or should not be trusted and spitting out > > patches and reports like the ones that are in the first few patches of > > this series. > > > > So please, pick a model, let's document it, and go with that. I am > > getting directly conflicting responses here. > > > > thanks, > > > > greg k-h > > Supposed to be this one: > Documentation/security/snp-tdx-threat-model.rst > > what is missing?
A policy decision that needs to be made. All that document does is describe a bunch of different "threats" yet does not decide what to do about them at all from what I can tell. And that's just for one subset of the CoC world, right? Is that something that all virtio drivers need/want to care about? So I don't see a real answer to the "does Linux trust the host to give you good data or not" question in that file, am I missing it? thanks, greg k-h
