[PATCH 3/3] cpufreq: qcom: fix writes in read-only memory region

From: Fabien Parent
Date: Sat Oct 01 2022 - 13:11:17 EST

This commit fixes a kernel oops because of a write in some read-only memory:

[ 9.068287] Unable to handle kernel write to read-only memory at virtual address ffff800009240ad8
[ 9.138790] Internal error: Oops: 9600004f [#1] PREEMPT SMP
[ 9.269161] Call trace:
[ 9.276271] __memcpy+0x5c/0x230
[ 9.278531] snprintf+0x58/0x80
[ 9.282002] qcom_cpufreq_msm8939_name_version+0xb4/0x190
[ 9.284869] qcom_cpufreq_probe+0xc8/0x39c

The following line defines a pointer that point to a char buffer stored
in read-only memory:

char *pvs_name = PVS_NAME;

This pointer is meant to hold a template "speedXX-pvsXX-vXX" where the
XX values get overridden by the qcom_cpufreq_krait_name_version function. Since
the template is actually stored in read-only memory, when the function
executes the following call we get an oops:

snprintf(*pvs_name, sizeof(PVS_NAME), "speed%d-pvs%d-v%d",
speed, pvs, pvs_ver);

To fix this issue, we instead store the template name onto the stack by
using the following syntax:

char pvs_name_buffer[] = PVS_NAME;

Because the `pvs_name` needs to be able to be assigned to NULL, the
template buffer is stored in the pvs_name_template and not under the
pvs_name variable.

Signed-off-by: Fabien Parent <fabien.parent@xxxxxxxxxx>
drivers/cpufreq/qcom-cpufreq-nvmem.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/cpufreq/qcom-cpufreq-nvmem.c b/drivers/cpufreq/qcom-cpufreq-nvmem.c
index 64ce077a4848..3e097262f612 100644
--- a/drivers/cpufreq/qcom-cpufreq-nvmem.c
+++ b/drivers/cpufreq/qcom-cpufreq-nvmem.c
@@ -269,7 +269,8 @@ static int qcom_cpufreq_probe(struct platform_device *pdev)
struct nvmem_cell *speedbin_nvmem;
struct device_node *np;
struct device *cpu_dev;
- char *pvs_name = PVS_NAME_TEMPLATE;
+ char pvs_name_buffer[] = PVS_NAME_TEMPLATE;
+ char *pvs_name = pvs_name_buffer;
unsigned cpu;
const struct of_device_id *match;
int ret;