gpio: prevent potential speculation leaks in gpio_device_get_desc()

JIRA: https://issues.redhat.com/browse/RHEL-56213
CVE: CVE-2024-44931

commit d795848
Author: Hagar Hemdan <hagarhem@amazon.com>
Date:   Thu May 23 08:53:32 2024 +0000

    gpio: prevent potential speculation leaks in gpio_device_get_desc()

    Userspace may trigger a speculative read of an address outside the gpio
    descriptor array.
    Users can do that by calling gpio_ioctl() with an offset out of range.
    Offset is copied from user and then used as an array index to get
    the gpio descriptor without sanitization in gpio_device_get_desc().

    This change ensures that the offset is sanitized by using
    array_index_nospec() to mitigate any possibility of speculative
    information leaks.

    This bug was discovered and resolved using Coverity Static Analysis
    Security Testing (SAST) by Synopsys, Inc.

    Signed-off-by: Hagar Hemdan <hagarhem@amazon.com>
    Link: https://lore.kernel.org/r/20240523085332.1801-1-hagarhem@amazon.com
    Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Signed-off-by: CKI Backport Bot <cki-ci-bot+cki-gitlab-backport-bot@redhat.com>

Author: CKI Backport Bot

drivers/gpio/gpiolib.c

@@ -15,6 +15,7 @@
 #include <linux/kernel.h>
 #include <linux/list.h>
 #include <linux/module.h>
+#include <linux/nospec.h>
 #include <linux/of.h>
 #include <linux/pinctrl/consumer.h>
 #include <linux/seq_file.h>
@@ -164,7 +165,7 @@ struct gpio_desc *gpiochip_get_desc(struct gpio_chip *gc,
 	if (hwnum >= gdev->ngpio)
 		return ERR_PTR(-EINVAL);
 
-	return &gdev->descs[hwnum];
+	return &gdev->descs[array_index_nospec(hwnum, gdev->ngpio)];
 }
 EXPORT_SYMBOL_GPL(gpiochip_get_desc);