pstore/blk: Introduce "best_effort" mode

In order to use arbitrary block devices as a pstore backend, provide a
new module param named "best_effort", which will allow using any block
device, even if it has not provided a panic_write callback.

Link: https://lore.kernel.org/lkml/20200511233229.27745-12-keescook@chromium.org/
Signed-off-by: Kees Cook <keescook@chromium.org>

diff --git a/fs/pstore/blk.c b/fs/pstore/blk.c
index 881b40e..fcd5563 100644 (file)
--- a/fs/pstore/blk.c
+++ b/fs/pstore/blk.c
@@ -51,6 +51,10 @@ static long ftrace_size = -1;
 module_param(ftrace_size, long, 0400);
 MODULE_PARM_DESC(ftrace_size, "ftrace size in kbytes");
 
+static bool best_effort;
+module_param(best_effort, bool, 0400);
+MODULE_PARM_DESC(best_effort, "use best effort to write (i.e. do not require storage driver pstore support, default: off)");
+
 /*
  * blkdev - the block device to use for pstore storage
  *
@@ -374,7 +378,8 @@ static int __register_pstore_blk(struct pstore_blk_info *info)
        }
 
        /* only allow driver matching the @blkdev */
-       if (!binfo.devt || MAJOR(binfo.devt) != info->major) {
+       if (!binfo.devt || (!best_effort &&
+                           MAJOR(binfo.devt) != info->major)) {
                pr_debug("invalid major %u (expect %u)\n",
                                info->major, MAJOR(binfo.devt));
                ret = -ENODEV;
@@ -476,6 +481,20 @@ int pstore_blk_get_config(struct pstore_blk_config *info)
 }
 EXPORT_SYMBOL_GPL(pstore_blk_get_config);
 
+static int __init pstore_blk_init(void)
+{
+       struct pstore_blk_info info = { };
+       int ret = 0;
+
+       mutex_lock(&pstore_blk_lock);
+       if (!pstore_zone_info && best_effort && blkdev[0])
+               ret = __register_pstore_blk(&info);
+       mutex_unlock(&pstore_blk_lock);
+
+       return ret;
+}
+late_initcall(pstore_blk_init);
+
 static void __exit pstore_blk_exit(void)
 {
        mutex_lock(&pstore_blk_lock);