x86/speculation/l1tf: Make sure the first page is always reserved

commit 10a70416e1f067f6c4efda6ffd8ea96002ac4223 upstream

The L1TF workaround doesn't make any attempt to mitigate speculate accesses
to the first physical page for zeroed PTEs. Normally it only contains some
data from the early real mode BIOS.

It's not entirely clear that the first page is reserved in all
configurations, so add an extra reservation call to make sure it is really
reserved. In most configurations (e.g.  with the standard reservations)
it's likely a nop.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Dave Hansen <dave.hansen@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index efbcf5283520ba28741388cb29b9e2cb5ede6376..dcb00acb6583c83432552f6032fb22f3d33fe980 100644 (file)
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -852,6 +852,12 @@ void __init setup_arch(char **cmdline_p)
        memblock_reserve(__pa_symbol(_text),
                         (unsigned long)__bss_stop - (unsigned long)_text);
 
+       /*
+        * Make sure page 0 is always reserved because on systems with
+        * L1TF its contents can be leaked to user processes.
+        */
+       memblock_reserve(0, PAGE_SIZE);
+
        early_reserve_initrd();
 
        /*