In the Linux kernel, the following vulnerability has been resolved: perf: arm_pmuv3: Zero initialize hw_id branch stack field PERF_SAMPLE_

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

perf: arm_pmuv3: Zero initialize hw_id branch stack field

PERF_SAMPLE_BRANCH_HW_INDEX is supported by BRBE so hw_id is passed to
userspace, but it's never set by the BRBE driver. Zero initialize it as
it should be according to the docs:

• For the architectures whose raw branch records are
• already stored in age order, the hw_idx should be 0.

It's probably too risky to remove PERF_SAMPLE_BRANCH_HW_INDEX from BRBE
now in case anyone is setting it and reading the value, but zero
initializing the whole struct also protects against the same issue with
new fields that are added in the future.