x86/mm/pti: Clone CPU_ENTRY_AREA on PMD level on x86_32

[uclinux-h8/linux.git] / arch / x86 / mm / pti.c

diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index 7921786..a594e3b 100644 (file)
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -348,6 +348,7 @@ pti_clone_pmds(unsigned long start, unsigned long end, pmdval_t clear)
        }
 }
 
+#ifdef CONFIG_X86_64
 /*
  * Clone a single p4d (i.e. a top-level entry on 4-level systems and a
  * next-level entry on 5-level systems.
@@ -371,6 +372,25 @@ static void __init pti_clone_user_shared(void)
        pti_clone_p4d(CPU_ENTRY_AREA_BASE);
 }
 
+#else /* CONFIG_X86_64 */
+
+/*
+ * On 32 bit PAE systems with 1GB of Kernel address space there is only
+ * one pgd/p4d for the whole kernel. Cloning that would map the whole
+ * address space into the user page-tables, making PTI useless. So clone
+ * the page-table on the PMD level to prevent that.
+ */
+static void __init pti_clone_user_shared(void)
+{
+       unsigned long start, end;
+
+       start = CPU_ENTRY_AREA_BASE;
+       end   = start + (PAGE_SIZE * CPU_ENTRY_AREA_PAGES);
+
+       pti_clone_pmds(start, end, 0);
+}
+#endif /* CONFIG_X86_64 */
+
 /*
  * Clone the ESPFIX P4D into the user space visible page table
  */