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

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>

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 2f86d883dd9508992adc57fcfcf3e8056554ebde..74b4472ba0a6453f4f3c42fafe2c45b302cab149 100644 (file)
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -823,6 +823,12 @@ 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();
 
        /*