platform/x86: dell-smbios-wmi: Avoid false-positive memcpy() warning

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memcpy(), memmove(), and memset(), avoid
intentionally writing across neighboring fields.

Since all the size checking has already happened, use input.pointer
(void *) so memcpy() doesn't get confused about how much is being
written.

Avoids this false-positive warning when run-time memcpy() strict
bounds checking is enabled:

memcpy: detected field-spanning write (size 4096) of single field (size 36)
WARNING: CPU: 0 PID: 357 at drivers/platform/x86/dell/dell-smbios-wmi.c:74 run_smbios_call+0x110/0x1e0 [dell_smbios]

Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Mark Gross <mgross@linux.intel.com>
Cc: Mario Limonciello <mario.limonciello@dell.com>
Cc: "Pali Rohár" <pali@kernel.org>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Cc: Dell.Client.Kernel@dell.com
Cc: platform-driver-x86@vger.kernel.org
Reported-by: Andy Lavr <andy.lavr@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210825160749.3891090-1-keescook@chromium.org
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

diff --git a/drivers/platform/x86/dell/dell-smbios-wmi.c b/drivers/platform/x86/dell/dell-smbios-wmi.c
index 33f8237..01ea4bb 100644 (file)
--- a/drivers/platform/x86/dell/dell-smbios-wmi.c
+++ b/drivers/platform/x86/dell/dell-smbios-wmi.c
@@ -71,7 +71,7 @@ static int run_smbios_call(struct wmi_device *wdev)
                                obj->integer.value);
                return -EIO;
        }
-       memcpy(&priv->buf->std, obj->buffer.pointer, obj->buffer.length);
+       memcpy(input.pointer, obj->buffer.pointer, obj->buffer.length);
        dev_dbg(&wdev->dev, "result: [%08x,%08x,%08x,%08x]\n",
                priv->buf->std.output[0], priv->buf->std.output[1],
                priv->buf->std.output[2], priv->buf->std.output[3]);