CVE-2026-53370

In the Linux kernel, the following vulnerability has been resolved:

perf/x86/intel: Improve validation and configuration of ACR masks

Currently there are several issues on the user space ACR mask validation
and configuration.
- The validation for user space ACR mask (attr.config2) is incomplete,
e.g., the ACR mask could include the index which belongs to another
ACR events group, but it's not validated.
- An early return on an invalid ACR mask caused all subsequent ACR groups
to be skipped.
- The stale hardware ACR mask (hw.config1) is not cleared before setting
new hardware ACR mask.

The following changes address all of the above issues.
- Figure out the event index group of an ACR group. Any bits in the
user-space mask not present in the index group are now dropped.
- Instead of an early return on invalid bits, drop only the invalid
portions and continue iterating through all ACR events to ensure full
configuration.
- Explicitly clear the stale hardware ACR mask for each event prior to
writing the new configuration.

Besides, a non-leader event member of ACR group could be disabled in
theory. This could cause bit-shifting errors in the acr_mask of remaining
group members. But since ACR sampling requires all events to be active,
this should not be a big concern in real use case. Add a "FIXME" comment
to notice this risk.