Hi Rafael, On Tue, May 17, 2022 at 9:06 AM Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote: > > On Mon, May 9, 2022 at 6:44 PM Evan Green <evgreen@xxxxxxxxxxxx> wrote: > > > > On Fri, May 6, 2022 at 9:08 AM Pavel Machek <pavel@xxxxxx> wrote: > > > > > > Hi! > > > > > > > We are exploring enabling hibernation in some new scenarios. However, > > > > our security team has a few requirements, listed below: > > > > 1. The hibernate image must be encrypted with protection derived from > > > > both the platform (eg TPM) and user authentication data (eg > > > > password). > > > > 2. Hibernation must not be a vector by which a malicious userspace can > > > > escalate to the kernel. > > > > > > Can you (or your security team) explain why requirement 2. is needed? > > > > > > On normal systems, trusted userspace handles kernel upgrades (for example), > > > so it can escalate to kernel priviledges. > > > > > > > Our systems are a little more sealed up than a normal distro, we use > > Verified Boot [1]. To summarize, RO firmware with an embedded public > > key verifies that the kernel+commandline was signed by Google. The > > commandline includes the root hash of the rootfs as well (where the > > modules live). So when an update is applied (A/B style, including the > > whole rootfs), assuming the RO firmware stayed RO (which requires > > physical measures to defeat), we can guarantee that the kernel, > > commandline, and rootfs have not been tampered with. > > > > Verified boot gives us confidence that on each boot, we're at least > > starting from known code. This makes it more challenging for an > > attacker to persist an exploit across reboot. With the kernel and > > modules verified, we try to make it non-trivial for someone who does > > manage to gain root execution once from escalating to kernel > > execution. Hibernation would be one obvious escalation route, so we're > > hoping to find a way to enable it without handing out that easy > > primitive. > > > > [1] https://www.chromium.org/chromium-os/chromiumos-design-docs/verified-boot/ > > So I guess this really is an RFC. Yes, I suppose it is. > > Honestly, I need more time to go through this and there are pieces of > it that need to be looked at other people (like the TPM-related > changes). No problem, thanks for the reply to let me know. I expect some back and forth in terms of what should be hidden behind abstractions and where exactly things should live. But I wanted to get this out to upstream as early as I could, just to get initial reactions on the overall concept and design. Looking forward to hearing your thoughts when you get a chance, and let me know if there are others I should be adding that I've missed. -Evan > > Thanks!
