Re: [PATCH v4 2/3] perf: enable unprivileged syscall tracing with perf trace

[Anubhav Shelat]

On Mon, May 18, 2026 at 5:41 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> Typically patches are supposed to a single thing, you're listing 4
> things. What gives?
All four changes need to be made together to work properly. The second
point could be pulled out as a separate patch, but will be replaced
with the eventfs that Steve suggested. The other three points
represent a single logical change: selectively loosening the
perf_event_open() restrictions without exposing kernel data or
breaking uprobe functionality.

> PERF_SAMPLE_IP should be here too, no?
If PERF_SAMPLE_IP is added to the kaddr_leak mask it blocks uprobes,
so the PERF_SAMPLE_IP check is in the trace_event_perf.c changes where
I can exempt uprobes:
+       if ((p_event->attr.sample_type & PERF_SAMPLE_IP) &&
+           !p_event->attr.exclude_kernel &&
+           !(tp_event->flags & TRACE_EVENT_FL_UPROBE) &&
+           sysctl_perf_event_paranoid > 1 && !perfmon_capable())
+               return -EACCES;

> And I'm not sure if tracepoints can trigger it, but PHYS_ADDR also seems
> something we shouldn't allow.
There's a check for unprivileged access to PHYS_ADDR at core.c:13917
so I didn't add it to kaddr_leak.

> And we're sure RAW doesn't include pointers
PERF_SAMPLE_RAW for TRACE_EVENT_FL_CAP_ANY tracepoints doesn't include
kernel pointers.

> Again, you're doing the same thing in multiple places. If only there was
> something to re-use a previous expression.
>
> None of this gives me warm and fuzzy feelings.
You're right. I'll factor the checks out for the next version.

Anubhav