On Tue, Aug 29, 2023 at 5:05 PM Mimi Zohar <zohar@xxxxxxxxxxxxx> wrote: > On Tue, 2023-08-29 at 15:34 -0400, Paul Moore wrote: > > On Mon, Aug 21, 2023 at 7:08 PM Mimi Zohar <zohar@xxxxxxxxxxxxx> wrote: > > > On Mon, 2023-08-21 at 15:05 -0700, Sush Shringarputale wrote: > > > > On 8/14/2023 3:02 PM, Mimi Zohar wrote: > > > > > On Mon, 2023-08-14 at 14:42 -0700, Sush Shringarputale wrote: > > > > >>> This design seems overly complex and requires synchronization between > > > > >>> the "snapshot" record and exporting the records from the measurement > > > > >>> list. None of this would be necessary if the measurements were copied > > > > >>> from kernel memory to a backing file (e.g. tmpfs), as described in [1]. > > > > Even if the Kernel maintains the link between a tmpfs exported and an > > > > in-memory IMA log - it still has to copy the tmpfs portion to the > > > > Kernel memory during kexec soft boot. tmpfs is cleared during kexec, > > > > so this copying of tmpfs back to kernel memory is necessary to preserve > > > > the integrity of the log during kexec. But the copying would add back > > > > the memory pressure on the node during kexec (which may result in > > > > out-of-memory), defeating the purpose of the overall effort/feature. > > > > Copying to a regular *persistent* protected file seems a cleaner > > > > approach, compared to tmpfs. > > > > > > From a kernel perspective, it doesn't make a difference if userspace > > > provides a tmpfs or persistent file. As per the discussion > > > https://lore.kernel.org/linux-integrity/CAOQ4uxj4Pv2Wr1wgvBCDR-tnA5dsZT3rvdDzKgAH1aEV_-r9Qg@xxxxxxxxxxxxxx/#t > > > , userspace provides the kernel with the file descriptor of the opened > > > file. > > > > > > > We prototyped this solution, however it > > > > does not seem to be a common pattern within the Kernel to write state > > > > directly to files on disk file systems. We considered two potential > > > > options: > > > > > > If no file descriptor is provided, then the measurements aren't copied > > > and removed from the securityfs file. If there are write errors, the > > > measurements aren't removed from the securityfs file until the write > > > errors are resolved. > > > > It sounds like this approach would require the file/filesystem to be > > continuously available for the life of the system once the log was > > snapshotted/overflowed to persistent storage, yes? Assuming that is > > the case, what happens if the file/filesystem becomes inaccessible at > > some point and an attestation client attempts to read the entire log? > > The main purpose of the change is to addres kernel memory pressure. > Two designs are being discussed: Sush's "snapshotting" design and > Amir's original suggestion of continously exporting the measurement > records to a tmpfs or regular file. Both designs require verifying the > initial attestation quote by walking the entire measurement list, > calculating the expected TPM PCR value(s). That doesn't change. Sure, but my question is about what happens if portions of the measurement list disappear due to file/filesystem problems? How is that handled? -- paul-moore.com
