perf: RISC-V: Limit the number of counters returned from SBI

Perf gets the number of supported counters from SBI. If it happens that
the number of returned counters more than RISCV_MAX_COUNTERS the code
trusts it. It does not lead to an immediate problem but can potentially
lead to it. Prevent getting more than RISCV_MAX_COUNTERS from SBI.

Signed-off-by: Viacheslav Mitrofanov <[e-mail]>
Reviewed-by: Andrew Jones <[e-mail]>
Reviewed-by: Atish Patra <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Palmer Dabbelt <[e-mail]>

drivers/perf/riscv_pmu_sbi.c

···
 		goto out_free;
 	}
 
+	/* It is possible to get from SBI more than max number of counters */
+	if (num_counters > RISCV_MAX_COUNTERS) {
+		num_counters = RISCV_MAX_COUNTERS;
+		pr_info("SBI returned more than maximum number of counters. Limiting the number of counters to %d\n", num_counters);
+	}
+
 	/* cache all the information about counters now */
 	if (pmu_sbi_get_ctrinfo(num_counters, &cmask))
 		goto out_free;