[PATCH v2] cpufreq: amd-pstate-ut: fix null pointer dereference

[Qianheng Peng]

The crash issue may occur when insmod amd_pstate_ut module on intel platform.

   amd_pstate_ut: 1    amd_pstate_ut_acpi_cpc_valid  success!
   amd_pstate_ut: 2    amd_pstate_ut_check_enabled   success!
   BUG: kernel NULL pointer dereference, address: 0000000000000080
   #PF: supervisor read access in kernel mode
   #PF: error_code(0x0000) - not-present page
   PGD 0 P4D 0
   Oops: 0000 [#1] SMP NOPTI
   CPU: 0 PID: 20300 Comm: modprobe
   Kdump: loaded Tainted: G O 6.6.0-0010.rc1.ctl4.x86_64 #1
   Hardware name: FiberHome R2200 V5/Xeon Boards, BIOS 3.1a 02/24/2020
   RIP: 0010:amd_pstate_ut_check_perf+0x141/0x280 [amd_pstate_ut]
   Call Trace:
    <TASK>
    amd_pstate_ut_init+0x1b/0xff0 [amd_pstate_ut]
    ? __pfx_amd_pstate_ut_init+0x10/0x10 [amd_pstate_ut]
    do_one_initcall+0x42/0x2e0
    ? kmalloc_trace+0x26/0x90
    do_init_module+0x60/0x240
    __se_sys_init_module+0x185/0x1c0
    do_syscall_64+0x62/0x190
    entry_SYSCALL_64_after_hwframe+0x76/0x7e
    </TASK>

Add invalidation check of cpudata in amd_pstate_ut_check_perf() and
amd_pstate_ut_check_freq() to avoid unpredicated null pointer dereference.
Otherwise, add driver name detection for amd_pstate_ut driver to prevent it
from testing cpufreq driver on non-amd platform.

Fixes: 14eb1c96e3a3 ("cpufreq: amd-pstate: Add test module for amd-pstate driver")
Suggested-by: Li Xiong <xiongl24@xxxxxxxxxxxxxxx>
Suggested-by: Xibo Wang <wangxb12@xxxxxxxxxxxxxxx>
Signed-off-by: Qianheng Peng <pengqh1@xxxxxxxxxxxxxxx>

---
v2:
  - Print policy->cpu instead of policy->kboj.name
  - Add cpufreq driver name detection to amd_pstate_ut

v1: https://lore.kernel.org/all/1784015941-26535-1-git-send-email-pengqh1@xxxxxxxxxxxxxxx
---
 drivers/cpufreq/amd-pstate-ut.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/drivers/cpufreq/amd-pstate-ut.c b/drivers/cpufreq/amd-pstate-ut.c
index 735b29f..5d71315 100644
--- a/drivers/cpufreq/amd-pstate-ut.c
+++ b/drivers/cpufreq/amd-pstate-ut.c
@@ -157,6 +157,10 @@ static int amd_pstate_ut_check_perf(u32 index)
 		if (!policy)
 			continue;
 		cpudata = policy->driver_data;
+		if (!cpudata) {
+			pr_err("%s empty driver_data on cpu %d\n", __func__, policy->cpu);
+			return -EINVAL;
+		}
 
 		if (get_shared_mem()) {
 			ret = cppc_get_perf_caps(cpu, &cppc_perf);
@@ -229,6 +233,10 @@ static int amd_pstate_ut_check_freq(u32 index)
 		if (!policy)
 			continue;
 		cpudata = policy->driver_data;
+		if (!cpudata) {
+			pr_err("%s empty driver_data on cpu %d\n", __func__, policy->cpu);
+			return -EINVAL;
+		}
 
 		if (!((policy->cpuinfo.max_freq >= cpudata->nominal_freq) &&
 			(cpudata->nominal_freq > cpudata->lowest_nonlinear_freq) &&
@@ -560,6 +568,15 @@ static int amd_pstate_ut_check_freq_attrs(u32 index)
 static int __init amd_pstate_ut_init(void)
 {
 	u32 i = 0, arr_size = ARRAY_SIZE(amd_pstate_ut_cases);
+	const char *driver_name = NULL;
+
+	driver_name = cpufreq_get_current_driver();
+	if (!driver_name)
+		return -ENOENT;
+	/* don't test if non-amd cpufreq_driver exists */
+	else if (strcmp(driver_name, "amd-pstate") &&
+		 strcmp(driver_name, "amd-pstate-epp"))
+		return -EEXIST;
 
 	for (i = 0; i < arr_size; i++) {
 		int ret;
-- 
1.8.3.1