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 | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index ce38f165489b..20be21301a59 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -308,6 +308,7 @@ 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.
@@ -322,13 +323,29 @@ static void __init pti_clone_p4d(unsigned long addr)
kernel_p4d = p4d_offset(kernel_pgd, addr);
*user_p4d = *kernel_p4d;
}
+#endif
/*
* Clone the CPU_ENTRY_AREA into the user space visible page table.
*/
static void __init pti_clone_user_shared(void)
{
+#ifdef CONFIG_X86_32
+ /*
+ * 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.
+ */
+ unsigned long start, end;
+
+ start = CPU_ENTRY_AREA_BASE;
+ end = start + (PAGE_SIZE * CPU_ENTRY_AREA_PAGES);
+
+ pti_clone_pmds(start, end, _PAGE_GLOBAL);
+#else
pti_clone_p4d(CPU_ENTRY_AREA_BASE);
+#endif
}
/*
--
2.13.6
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