x86, microcode: Return error from driver init code when loader is disabled

Commits 65cef1311d5d ("x86, microcode: Add a disable chicken bit") and
a18a0f6850d4 ("x86, microcode: Don't initialize microcode code on
paravirt") allow microcode driver skip initialization when microcode
loading is not permitted.

However, they don't prevent the driver from being loaded since the
init code returns 0. If at some point later the driver gets unloaded
this will result in an oops while trying to deregister the (never
registered) device.

To avoid this, make init code return an error on paravirt or when
microcode loading is disabled. The driver will then never be loaded.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Link: http://lkml.kernel.org/r/1422411669-25147-1-git-send-email-boris.ostrovsky@oracle.com
Reported-by: James Digwall <james@dingwall.me.uk>
Cc: stable@vger.kernel.org # 3.18
Signed-off-by: Borislav Petkov <bp@suse.de>

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index 15c29096136ba5e071c213d1412004740aa1f459..36a83617eb21cc19245794a89c986eba45179d3a 100644 (file)
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -552,7 +552,7 @@ static int __init microcode_init(void)
        int error;
 
        if (paravirt_enabled() || dis_ucode_ldr)
-               return 0;
+               return -EINVAL;
 
        if (c->x86_vendor == X86_VENDOR_INTEL)
                microcode_ops = init_intel_microcode();