Matthew Garrett <mjg59@xxxxxxxxxx> writes: > On Tue, Apr 16, 2019 at 1:40 AM Andrew Donnellan > <andrew.donnellan@xxxxxxxxxxx> wrote: >> I'm thinking about whether we should lock down the powerpc xmon debug >> monitor - intuitively, I think the answer is yes if for no other reason >> than Least Astonishment, when lockdown is enabled you probably don't >> expect xmon to keep letting you access kernel memory. > > The original patchset contained a sysrq hotkey to allow physically > present users to disable lockdown, so I'm not super concerned about > this case - I could definitely be convinced otherwise, though. So currently (and I'm pretty new to this as I've only recently rejoined IBM) we aren't considering access to the console to be sufficient to assert physical presence on bare-metal server-class Power machines. The short argument for this is that with IPMI and BMCs, a server's console isn't what it used to be. Our console is also a bit different to x86: we don't generally have bios configuration screens on the console. In your example, a sysrq key would allow you to disable lockdown after the system has booted. On Power though, we use Linux as a bootloader (Petitboot: https://github.com/open-power/petitboot) so being able to disable lockdown there allows an IPMI-connected user to prevent a signed kernel being loaded in the first place. I don't know if this is _actually_ worse, but it certainly feels worse. There are of course some arguments against our approach. I'm aware of some of them. I'm also very open to being told that not equating console access with physical access is fundamentally silly or broken and that we should rethink things. Regards, Daniel
