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. -- MST
