linux-hardening - [PATCH v3] cpufreq: brcmstb-avs-cpufreq: Fix -Warray-bounds bug

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Date:   Mon, 31 Jul 2023 21:15:48 -0600
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     Markus Mayer <mmayer@...adcom.com>,
        Broadcom internal kernel review list 
        <bcm-kernel-feedback-list@...adcom.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Florian Fainelli <florian.fainelli@...adcom.com>
Cc:     linux-pm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-hardening@...r.kernel.org, Kees Cook <keescook@...omium.org>
Subject: [PATCH v3] cpufreq: brcmstb-avs-cpufreq: Fix -Warray-bounds bug

Allocate extra space for terminating element at:

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

and add code comment to make this clear.

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.

Link: https://github.com/KSPP/linux/issues/324
Fixes: de322e085995 ("cpufreq: brcmstb-avs-cpufreq: AVS CPUfreq driver for Broadcom STB SoCs")
Cc: stable@...r.kernel.org
Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
---
Changes in v3:
 - Allocate extra space for a terminating element. (Kees Cook)
 - Update changelog text.

Changes in v2:
 - Update changelog text. Add more details.
 - Link: https://lore.kernel.org/linux-hardening/202307311610.B1EB796684@keescook/

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

 drivers/cpufreq/brcmstb-avs-cpufreq.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/cpufreq/brcmstb-avs-cpufreq.c b/drivers/cpufreq/brcmstb-avs-cpufreq.c
index ffea6402189d..3052949aebbc 100644
--- a/drivers/cpufreq/brcmstb-avs-cpufreq.c
+++ b/drivers/cpufreq/brcmstb-avs-cpufreq.c
@@ -434,7 +434,11 @@ brcm_avs_get_freq_table(struct device *dev, struct private_data *priv)
 	if (ret)
 		return ERR_PTR(ret);
 
-	table = devm_kcalloc(dev, AVS_PSTATE_MAX + 1, sizeof(*table),
+	/*
+	 * We allocate space for the 5 different P-STATES AVS,
+	 * plus extra space for a terminating element.
+	 */
+	table = devm_kcalloc(dev, AVS_PSTATE_MAX + 1 + 1, sizeof(*table),
 			     GFP_KERNEL);
 	if (!table)
 		return ERR_PTR(-ENOMEM);
-- 
2.34.1