On Mon, Oct 14, 2019 at 01:03:08PM -0400, Joel Fernandes (Google) wrote: > In current mainline, the degree of access to perf_event_open(2) system > call depends on the perf_event_paranoid sysctl. This has a number of > limitations: > > 1. The sysctl is only a single value. Many types of accesses are controlled > based on the single value thus making the control very limited and > coarse grained. > 2. The sysctl is global, so if the sysctl is changed, then that means > all processes get access to perf_event_open(2) opening the door to > security issues. > > This patch adds LSM and SELinux access checking which will be used in > Android to access perf_event_open(2) for the purposes of attaching BPF > programs to tracepoints, perf profiling and other operations from > userspace. These operations are intended for production systems. > > 5 new LSM hooks are added: > 1. perf_event_open: This controls access during the perf_event_open(2) > syscall itself. The hook is called from all the places that the > perf_event_paranoid sysctl is checked to keep it consistent with the > systctl. The hook gets passed a 'type' argument which controls CPU, > kernel and tracepoint accesses (in this context, CPU, kernel and > tracepoint have the same semantics as the perf_event_paranoid sysctl). > Additionally, I added an 'open' type which is similar to > perf_event_paranoid sysctl == 3 patch carried in Android and several other > distros but was rejected in mainline [1] in 2016. > > 2. perf_event_alloc: This allocates a new security object for the event > which stores the current SID within the event. It will be useful when > the perf event's FD is passed through IPC to another process which may > try to read the FD. Appropriate security checks will limit access. > > 3. perf_event_free: Called when the event is closed. > > 4. perf_event_read: Called from the read(2) and mmap(2) syscalls for the event. > > 5. perf_event_write: Called from the ioctl(2) syscalls for the event. > > [1] https://lwn.net/Articles/696240/ > > Since Peter had suggest LSM hooks in 2016 [1], I am adding his > Suggested-by tag below. Thanks, I've queued the patch! > To use this patch, we set the perf_event_paranoid sysctl to -1 and then > apply selinux checking as appropriate (default deny everything, and then > add policy rules to give access to domains that need it). In the future > we can remove the perf_event_paranoid sysctl altogether. This I'm not sure about; the sysctl is only redundant when you actually use a security thingy, not everyone is. I always find them things to be mightily unfriendly.
