x86, mm: Report state of NX protections during boot

It is possible for x86_64 systems to lack the NX bit either due to the
hardware lacking support or the BIOS having turned off the CPU capability,
so NX status should be reported.  Additionally, anyone booting NX-capable
CPUs in 32bit mode without PAE will lack NX functionality, so this change
provides feedback for that case as well.

Signed-off-by: Kees Cook <kees.cook@canonical.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
LKML-Reference: <1258154897-6770-6-git-send-email-hpa@zytor.com>

2 files changed, 22 insertions, 4 deletions

diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index 27ec2c23fd4..d406c523901 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -146,10 +146,6 @@ unsigned long __init_refok init_memory_mapping(unsigned long start,
         use_gbpages = direct_gbpages;
 #endif
 
-        /* XXX: replace this with Kees' improved messages */
-        if (__supported_pte_mask & _PAGE_NX)
-                printk(KERN_INFO "NX (Execute Disable) protection: active\n");
-
         /* Enable PSE if available */
         if (cpu_has_pse)
                 set_in_cr4(X86_CR4_PSE);
diff --git a/arch/x86/mm/setup_nx.c b/arch/x86/mm/setup_nx.c
index 355818b087b..a3250aa3408 100644
--- a/arch/x86/mm/setup_nx.c
+++ b/arch/x86/mm/setup_nx.c
@@ -36,3 +36,25 @@ void __cpuinit x86_configure_nx(void)
         else
                 __supported_pte_mask &= ~_PAGE_NX;
 }
+
+void __init x86_report_nx(void)
+{
+        if (!cpu_has_nx) {
+                printk(KERN_NOTICE "Notice: NX (Execute Disable) protection "
+                       "missing in CPU or disabled in BIOS!\n");
+        } else {
+#if defined(CONFIG_X86_64) || defined(CONFIG_X86_PAE)
+                if (disable_nx) {
+                        printk(KERN_INFO "NX (Execute Disable) protection: "
+                               "disabled by kernel command line option\n");
+                } else {
+                        printk(KERN_INFO "NX (Execute Disable) protection: "
+                               "active\n");
+                }
+#else
+                /* 32bit non-PAE kernel, NX cannot be used */
+                printk(KERN_NOTICE "Notice: NX (Execute Disable) protection "
+                       "cannot be enabled: non-PAE kernel!\n");
+#endif
+        }
+}