CVE-2026-97587

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

perf: RISC-V: store available counter mask as bitmap

The available-counter mask was a single unsigned long, but iteration
uses RISCV_MAX_COUNTERS, which is 64. On RV32 that reads past the object.
Filling with an unsigned-long bit at index 32 and above is also wrong.

Use DECLARE_BITMAP and set_bit/bitmap helpers. Walk each bitmap word
into CFG_MATCH when checking events, when allocating an index, and when
stopping all counters. Set the counter base to i times BITS_PER_LONG.
Share the CFG_MATCH ecall through a small helper so the 32-bit argument
split is not duplicated. On qemu-system-riscv32 the probe bitmap has bits
above XLEN set, so the first word alone is not enough.

[pjw@kernel.org: updated to apply; fixed checkpatch.pl issues]