powerpc/rfi-flush: Move the logic to avoid a redo into the debugfs code

rfi_flush_enable() includes a check to see if we're already
enabled (or disabled), and in that case does nothing.

But that means calling setup_rfi_flush() a 2nd time doesn't actually
work, which is a bit confusing.

Move that check into the debugfs code, where it really belongs.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
(cherry picked from commit 1e2a9fc7496955faacbbed49461d611b704a7505)

CVE-2018-3639 (powerpc)

Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
index 3ac85e92892ab10fd44ed9e11aced1af37cc237e..c0d40563aef7ad9721051cebf40cc4144d96779f 100644 (file)
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -789,9 +789,6 @@ static void do_nothing(void *unused)
 
 void rfi_flush_enable(bool enable)
 {
-       if (rfi_flush == enable)
-               return;
-
        if (enable) {
                do_rfi_flush_fixups(enabled_flush_types);
                on_each_cpu(do_nothing, NULL, 1);
@@ -852,13 +849,19 @@ void __init setup_rfi_flush(enum l1d_flush_type types, bool enable)
 #ifdef CONFIG_DEBUG_FS
 static int rfi_flush_set(void *data, u64 val)
 {
+       bool enable;
+
        if (val == 1)
-               rfi_flush_enable(true);
+               enable = true;
        else if (val == 0)
-               rfi_flush_enable(false);
+               enable = false;
        else
                return -EINVAL;
 
+       /* Only do anything if we're changing state */
+       if (enable != rfi_flush)
+               rfi_flush_enable(enable);
+
        return 0;
 }