x86/mm: Move LDT remap out of KASLR region on 5-level paging

On 5-level paging the LDT remap area is placed in the middle of the KASLR
randomization region and it can overlap with the direct mapping, the
vmalloc or the vmap area.

The LDT mapping is per mm, so it cannot be moved into the P4D page table
next to the CPU_ENTRY_AREA without complicating PGD table allocation for
5-level paging.

The 4 PGD slot gap just before the direct mapping is reserved for
hypervisors, so it cannot be used.

Move the direct mapping one slot deeper and use the resulting gap for the
LDT remap area. The resulting layout is the same for 4 and 5 level paging.

[ tglx: Massaged changelog ]

Fixes: f55f0501cbf6 ("x86/pti: Put the LDT in its own PGD if PTI is on")
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Andy Lutomirski <luto@kernel.org>
Cc: bp@alien8.de
Cc: hpa@zytor.com
Cc: dave.hansen@linux.intel.com
Cc: peterz@infradead.org
Cc: boris.ostrovsky@oracle.com
Cc: jgross@suse.com
Cc: bhe@redhat.com
Cc: willy@infradead.org
Cc: linux-mm@kvack.org
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20181026122856.66224-2-kirill.shutemov@linux.intel.com

1 files changed, 3 insertions, 3 deletions

diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c
index 0d7b3ae4960b..a5d7ed125337 100644
--- a/arch/x86/xen/mmu_pv.c
+++ b/arch/x86/xen/mmu_pv.c
@@ -1905,7 +1905,7 @@ void __init xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn)
         init_top_pgt[0] = __pgd(0);
 
         /* Pre-constructed entries are in pfn, so convert to mfn */
-        /* L4[272] -> level3_ident_pgt  */
+        /* L4[273] -> level3_ident_pgt  */
         /* L4[511] -> level3_kernel_pgt */
         convert_pfn_mfn(init_top_pgt);
 
@@ -1925,8 +1925,8 @@ void __init xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn)
         addr[0] = (unsigned long)pgd;
         addr[1] = (unsigned long)l3;
         addr[2] = (unsigned long)l2;
-        /* Graft it onto L4[272][0]. Note that we creating an aliasing problem:
-         * Both L4[272][0] and L4[511][510] have entries that point to the same
+        /* Graft it onto L4[273][0]. Note that we creating an aliasing problem:
+         * Both L4[273][0] and L4[511][510] have entries that point to the same
          * L2 (PMD) tables. Meaning that if you modify it in __va space
          * it will be also modified in the __ka space! (But if you just
          * modify the PMD table to point to other PTE's or none, then you