clk: Emit a stern warning with writable debugfs enabled

BugLink: https://bugs.launchpad.net/bugs/1959376
commit 489a71964f9d74e697a12cd0ace20ed829eb1f93 upstream.

We don't want vendors to be enabling this part of the clk code and
shipping it to customers. Exposing the ability to change clk frequencies
and parents via debugfs is potentially damaging to the system if folks
don't know what they're doing. Emit a strong warning so that the message
is clear: don't enable this outside of development systems.

Fixes: 37215da5553e ("clk: Add support for setting clk_rate via debugfs")
Cc: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20211210014237.2130300-1-sboyd@kernel.org
Signed-off-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index a277fd4f2f0a6a57f31e535f9378d46d210d6075..ac11cefc319111f7b9acec3db0f15580100ad172 100644 (file)
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -3340,6 +3340,24 @@ static int __init clk_debug_init(void)
 {
        struct clk_core *core;
 
+#ifdef CLOCK_ALLOW_WRITE_DEBUGFS
+       pr_warn("\n");
+       pr_warn("********************************************************************\n");
+       pr_warn("**     NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE           **\n");
+       pr_warn("**                                                                **\n");
+       pr_warn("**  WRITEABLE clk DebugFS SUPPORT HAS BEEN ENABLED IN THIS KERNEL **\n");
+       pr_warn("**                                                                **\n");
+       pr_warn("** This means that this kernel is built to expose clk operations  **\n");
+       pr_warn("** such as parent or rate setting, enabling, disabling, etc.      **\n");
+       pr_warn("** to userspace, which may compromise security on your system.    **\n");
+       pr_warn("**                                                                **\n");
+       pr_warn("** If you see this message and you are not debugging the          **\n");
+       pr_warn("** kernel, report this immediately to your vendor!                **\n");
+       pr_warn("**                                                                **\n");
+       pr_warn("**     NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE           **\n");
+       pr_warn("********************************************************************\n");
+#endif
+
        rootdir = debugfs_create_dir("clk", NULL);
 
        debugfs_create_file("clk_summary", 0444, rootdir, &all_lists,