cpufreq: brcmstb-avs-cpufreq: Fix -Warray-bounds bug

Update the iteration conditions in the for() loop to avoid writing in array table beyond its allocated size at:

drivers/cpufreq/brcmstb-avs-cpufreq.c:
449 table[i].frequency = CPUFREQ_TABLE_END;

This fixes the following -Warray-bounds warning seen after building
ARM with multi_v7_defconfig (GCC 13):
In function 'brcm_avs_get_freq_table',
inlined from 'brcm_avs_cpufreq_init' at drivers/cpufreq/brcmstb-avs-cpufreq.c:623:15:
drivers/cpufreq/brcmstb-avs-cpufreq.c:449:28: warning: array subscript 5 is outside array bounds of 'void[60]' [-Warray-bounds=]
449 | table[i].frequency = CPUFREQ_TABLE_END;
In file included from include/linux/node.h:18,
from include/linux/cpu.h:17,
from include/linux/cpufreq.h:12,
from drivers/cpufreq/brcmstb-avs-cpufreq.c:44:
In function 'devm_kmalloc_array',
inlined from 'devm_kcalloc' at include/linux/device.h:328:9,
inlined from 'brcm_avs_get_freq_table' at drivers/cpufreq/brcmstb-avs-cpufreq.c:437:10,
inlined from 'brcm_avs_cpufreq_init' at drivers/cpufreq/brcmstb-avs-cpufreq.c:623:15:
include/linux/device.h:323:16: note: at offset 60 into object of size 60 allocated by 'devm_kmalloc'

  323 |         return devm_kmalloc(dev, bytes, flags);
      |                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This helps with the ongoing efforts to tighten the FORTIFY_SOURCE routines on memcpy() and help us make progress towards globally enabling -Warray-bounds.

---
Changes in v2:
- Update changelog text. Add more details.

v1:
- Link: https://lore.kernel.org/linux-hardening/ZMgfWEA0GAN%2FRog8@work/

 drivers/cpufreq/brcmstb-avs-cpufreq.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 1bdd513bcd19..99ba2d707eff 100644
@@ -439,7 +439,7 @@ brcm_avs_get_freq_table(struct device *dev, struct private_data *priv)
 	if (!table)
 		return ERR_PTR(-ENOMEM);
 
-	for (i = AVS_PSTATE_P0; i <= AVS_PSTATE_MAX; i++) {
+	for (i = AVS_PSTATE_P0; i < AVS_PSTATE_MAX; i++) {
 		ret = brcm_avs_set_pstate(priv, i);
 		if (ret)
 			return ERR_PTR(ret);

2.34.1

#define AVS_PSTATE_P0           0x0
#define AVS_PSTATE_P1           0x1
#define AVS_PSTATE_P2           0x2
#define AVS_PSTATE_P3           0x3
#define AVS_PSTATE_P4           0x4
#define AVS_PSTATE_MAX          AVS_PSTATE_P4

        table = devm_kcalloc(dev, AVS_PSTATE_MAX + 1, sizeof(*table),
                             GFP_KERNEL);
	...
        for (i = AVS_PSTATE_P0; i <= AVS_PSTATE_MAX; i++) {
		...
	}
        table[i].frequency = CPUFREQ_TABLE_END;

I see "AVS_PSTATE_MAX + 1" being used for the allocation, and so the loop is likely correctly doing P0 through P4. If there is supposed to be a terminating element in the table, I think the correct fix would be to allocate an additional element, not stop the loop from processing P4.

Kees Cook

Yeah; I think you're right. And it seems that this function header makes it clear, too:

drivers/cpufreq/brcmstb-avs-cpufreq.c:
421 /*

422  * We determine which frequencies are supported by cycling through all P-states
423  * and reading back what frequency we are running at for each P-state.
424  */

425 static struct cpufreq_frequency_table *
426 brcm_avs_get_freq_table(struct device *dev, struct private_data *priv)

I just sent v3:
https://lore.kernel.org/linux-hardening/ZMh45KH2iPIpNktr@work/

Let's see what the maintainers say.

Thanks for the feedback!
--
Gustavo