Peter Zijlstra <pet...@infradead.org> writes: > On Tue, Feb 23, 2021 at 01:31:49AM -0500, Athira Rajeev wrote: >> Running "perf mem record" in powerpc platforms with selinux enabled >> resulted in soft lockup's. Below call-trace was seen in the logs: ... >> >> Since the purpose of this security hook is to control access to >> perf_event_open, it is not right to call this in interrupt context. >> But in case of powerpc PMU, we need the privilege checks for specific >> samples from branch history ring buffer and sampling register values. > > I'm confused... why would you need those checks at event time? Either > the event has perf_event_attr::exclude_kernel and it then isn't allowed > to expose kernel addresses, or it doesn't and it is.
Well one of us is confused that's for sure ^_^ I missed/forgot that we had that logic in open. I think the reason we got here is that in the past we didn't have the event in the low-level routines where we want to check, power_pmu_bhrb_read() and perf_get_data_addr(), so we hacked in a perf_paranoid_kernel() check. Which was wrong. Then Joel's patch plumbed the event through and switched those paranoid checks to perf_allow_kernel(). Anyway, we'll just switch those to exclude_kernel checks. > There should never be an event-time question of permission like this. If > you allow creation of an event, you're allowing the data it generates. Ack. cheers
