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: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index bbaae4cf9e8edd9dd779aaf8d550a02760f0ee07..31c4bc0d3372c6999e55ed2352ed4f65f349ffa2 100644 (file)
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -851,6 +851,12 @@ 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();
 
        /*