powerpc/64s: Allow control of RFI flush via debugfs

Expose the state of the RFI flush (enabled/disabled) via debugfs, and
allow it to be enabled/disabled at runtime.

eg: $ cat /sys/kernel/debug/powerpc/rfi_flush
    1
    $ echo 0 > /sys/kernel/debug/powerpc/rfi_flush
    $ cat /sys/kernel/debug/powerpc/rfi_flush
    0

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
[mauricio: backport: hunk 2: update context lines for end of file]
Signed-off-by: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>
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 abb226c063aba62433df75bb9893a468d2a7f806..3ac85e92892ab10fd44ed9e11aced1af37cc237e 100644 (file)
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -38,6 +38,7 @@
 #include <linux/memory.h>
 #include <linux/nmi.h>
 
+#include <asm/debugfs.h>
 #include <asm/io.h>
 #include <asm/kdump.h>
 #include <asm/prom.h>
@@ -847,4 +848,34 @@ void __init setup_rfi_flush(enum l1d_flush_type types, bool enable)
        if (!no_rfi_flush)
                rfi_flush_enable(enable);
 }
+
+#ifdef CONFIG_DEBUG_FS
+static int rfi_flush_set(void *data, u64 val)
+{
+       if (val == 1)
+               rfi_flush_enable(true);
+       else if (val == 0)
+               rfi_flush_enable(false);
+       else
+               return -EINVAL;
+
+       return 0;
+}
+
+static int rfi_flush_get(void *data, u64 *val)
+{
+       *val = rfi_flush ? 1 : 0;
+       return 0;
+}
+
+DEFINE_SIMPLE_ATTRIBUTE(fops_rfi_flush, rfi_flush_get, rfi_flush_set, "%llu\n");
+
+static __init int rfi_flush_debugfs_init(void)
+{
+       debugfs_create_file("rfi_flush", 0600, powerpc_debugfs_root, NULL, &fops_rfi_flush);
+       return 0;
+}
+device_initcall(rfi_flush_debugfs_init);
+#endif
+
 #endif /* CONFIG_PPC_BOOK3S_64 */