Re: [PATCH v2] cpufreq: brcmstb-avs-cpufreq: Fix -Warray-bounds bug

[Gustavo A. R. Silva]

On 7/31/23 17:16, Kees Cook wrote:
> On Mon, Jul 31, 2023 at 03:07:20PM -0600, Gustavo A. R. Silva wrote:
> > 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;
>
> #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.

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