firmware: enable to force disable the fallback mechanism at run time

You currently need four different kernel builds to test the firmware
API fully. By adding a proc knob to force disable the fallback mechanism
completely we are able to reduce the amount of kernels you need built
to test the firmware API down to two.

Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

3 files changed, 18 insertions, 0 deletions

diff --git a/drivers/base/firmware_loader/fallback.c b/drivers/base/firmware_loader/fallback.c
index 45cc40933a47..d6838e7ec00c 100644
--- a/drivers/base/firmware_loader/fallback.c
+++ b/drivers/base/firmware_loader/fallback.c
@@ -643,6 +643,11 @@ static bool fw_force_sysfs_fallback(unsigned int opt_flags)
 
 static bool fw_run_sysfs_fallback(unsigned int opt_flags)
 {
+        if (fw_fallback_config.ignore_sysfs_fallback) {
+                pr_info_once("Ignoring firmware sysfs fallback due to debugfs knob\n");
+                return false;
+        }
+
         if ((opt_flags & FW_OPT_NOFALLBACK))
                 return false;
 
diff --git a/drivers/base/firmware_loader/fallback.h b/drivers/base/firmware_loader/fallback.h
index ca7e69a8417b..dfebc644ed35 100644
--- a/drivers/base/firmware_loader/fallback.h
+++ b/drivers/base/firmware_loader/fallback.h
@@ -14,12 +14,16 @@
  *      as if one had enabled CONFIG_FW_LOADER_USER_HELPER_FALLBACK=y.
  *      Useful to help debug a CONFIG_FW_LOADER_USER_HELPER_FALLBACK=y
  *      functionality on a kernel where that config entry has been disabled.
+ * @ignore_sysfs_fallback: force to disable the sysfs fallback mechanism.
+ *      This emulates the behaviour as if we had set the kernel
+ *      config CONFIG_FW_LOADER_USER_HELPER=n.
  * @old_timeout: for internal use
  * @loading_timeout: the timeout to wait for the fallback mechanism before
  *      giving up, in seconds.
  */
 struct firmware_fallback_config {
         unsigned int force_sysfs_fallback;
+        unsigned int ignore_sysfs_fallback;
         int old_timeout;
         int loading_timeout;
 };
diff --git a/drivers/base/firmware_loader/fallback_table.c b/drivers/base/firmware_loader/fallback_table.c
index 92365e053e30..7428659d8df9 100644
--- a/drivers/base/firmware_loader/fallback_table.c
+++ b/drivers/base/firmware_loader/fallback_table.c
@@ -39,6 +39,15 @@ struct ctl_table firmware_config_table[] = {
                 .extra1         = &zero,
                 .extra2         = &one,
         },
+        {
+                .procname       = "ignore_sysfs_fallback",
+                .data           = &fw_fallback_config.ignore_sysfs_fallback,
+                .maxlen         = sizeof(unsigned int),
+                .mode           = 0644,
+                .proc_handler   = proc_douintvec_minmax,
+                .extra1         = &zero,
+                .extra2         = &one,
+        },
         { }
 };
 EXPORT_SYMBOL_GPL(firmware_config_table);