From: Joerg Roedel <jroedel@xxxxxxx>
Cloning on the P4D level would clone the complete kernel
address space into the user-space page-tables for PAE
kernels. Cloning on PMD level is fine for PAE and legacy
paging.
Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
---
arch/x86/mm/pti.c | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)
diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index f967b51..9cceae3 100644
--- 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
*/
--
2.7.4
