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? -- paul-moore.com
