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, 18 insertions, 16 deletions

diff --git a/Documentation/x86/x86_64/mm.txt b/Documentation/x86/x86_64/mm.txt
index 73aaaa3da436..804f9426ed17 100644
--- a/Documentation/x86/x86_64/mm.txt
+++ b/Documentation/x86/x86_64/mm.txt
@@ -34,23 +34,24 @@ __________________|____________|__________________|_________|___________________
 ____________________________________________________________|___________________________________________________________
                   |            |                  |         |
  ffff800000000000 | -128    TB | ffff87ffffffffff |    8 TB | ... guard hole, also reserved for hypervisor
- ffff880000000000 | -120    TB | ffffc7ffffffffff |   64 TB | direct mapping of all physical memory (page_offset_base)
- ffffc80000000000 |  -56    TB | ffffc8ffffffffff |    1 TB | ... unused hole
+ ffff880000000000 | -120    TB | ffff887fffffffff |  0.5 TB | LDT remap for PTI
+ ffff888000000000 | -119.5  TB | ffffc87fffffffff |   64 TB | direct mapping of all physical memory (page_offset_base)
+ ffffc88000000000 |  -55.5  TB | ffffc8ffffffffff |  0.5 TB | ... unused hole
  ffffc90000000000 |  -55    TB | ffffe8ffffffffff |   32 TB | vmalloc/ioremap space (vmalloc_base)
  ffffe90000000000 |  -23    TB | ffffe9ffffffffff |    1 TB | ... unused hole
  ffffea0000000000 |  -22    TB | ffffeaffffffffff |    1 TB | virtual memory map (vmemmap_base)
  ffffeb0000000000 |  -21    TB | ffffebffffffffff |    1 TB | ... unused hole
  ffffec0000000000 |  -20    TB | fffffbffffffffff |   16 TB | KASAN shadow memory
- fffffc0000000000 |   -4    TB | fffffdffffffffff |    2 TB | ... unused hole
-                  |            |                  |         | vaddr_end for KASLR
- fffffe0000000000 |   -2    TB | fffffe7fffffffff |  0.5 TB | cpu_entry_area mapping
- fffffe8000000000 |   -1.5  TB | fffffeffffffffff |  0.5 TB | LDT remap for PTI
- ffffff0000000000 |   -1    TB | ffffff7fffffffff |  0.5 TB | %esp fixup stacks
 __________________|____________|__________________|_________|____________________________________________________________
                                                             |
-                                                            | Identical layout to the 47-bit one from here on:
+                                                            | Identical layout to the 56-bit one from here on:
 ____________________________________________________________|____________________________________________________________
                   |            |                  |         |
+ fffffc0000000000 |   -4    TB | fffffdffffffffff |    2 TB | ... unused hole
+                  |            |                  |         | vaddr_end for KASLR
+ fffffe0000000000 |   -2    TB | fffffe7fffffffff |  0.5 TB | cpu_entry_area mapping
+ fffffe8000000000 |   -1.5  TB | fffffeffffffffff |  0.5 TB | ... unused hole
+ ffffff0000000000 |   -1    TB | ffffff7fffffffff |  0.5 TB | %esp fixup stacks
  ffffff8000000000 | -512    GB | ffffffeeffffffff |  444 GB | ... unused hole
  ffffffef00000000 |  -68    GB | fffffffeffffffff |   64 GB | EFI region mapping space
  ffffffff00000000 |   -4    GB | ffffffff7fffffff |    2 GB | ... unused hole
@@ -83,7 +84,7 @@ Notes:
 __________________|____________|__________________|_________|___________________________________________________________
                   |            |                  |         |
  0000800000000000 |  +64    PB | ffff7fffffffffff | ~16K PB | ... huge, still almost 64 bits wide hole of non-canonical
-                  |            |                  |         |     virtual memory addresses up to the -128 TB
+                  |            |                  |         |     virtual memory addresses up to the -64 PB
                   |            |                  |         |     starting offset of kernel mappings.
 __________________|____________|__________________|_________|___________________________________________________________
                                                             |
@@ -91,23 +92,24 @@ __________________|____________|__________________|_________|___________________
 ____________________________________________________________|___________________________________________________________
                   |            |                  |         |
  ff00000000000000 |  -64    PB | ff0fffffffffffff |    4 PB | ... guard hole, also reserved for hypervisor
- ff10000000000000 |  -60    PB | ff8fffffffffffff |   32 PB | direct mapping of all physical memory (page_offset_base)
- ff90000000000000 |  -28    PB | ff9fffffffffffff |    4 PB | LDT remap for PTI
+ ff10000000000000 |  -60    PB | ff10ffffffffffff | 0.25 PB | LDT remap for PTI
+ ff11000000000000 |  -59.75 PB | ff90ffffffffffff |   32 PB | direct mapping of all physical memory (page_offset_base)
+ ff91000000000000 |  -27.75 PB | ff9fffffffffffff | 3.75 PB | ... unused hole
  ffa0000000000000 |  -24    PB | ffd1ffffffffffff | 12.5 PB | vmalloc/ioremap space (vmalloc_base)
  ffd2000000000000 |  -11.5  PB | ffd3ffffffffffff |  0.5 PB | ... unused hole
  ffd4000000000000 |  -11    PB | ffd5ffffffffffff |  0.5 PB | virtual memory map (vmemmap_base)
  ffd6000000000000 |  -10.5  PB | ffdeffffffffffff | 2.25 PB | ... unused hole
  ffdf000000000000 |   -8.25 PB | fffffdffffffffff |   ~8 PB | KASAN shadow memory
- fffffc0000000000 |   -4    TB | fffffdffffffffff |    2 TB | ... unused hole
-                  |            |                  |         | vaddr_end for KASLR
- fffffe0000000000 |   -2    TB | fffffe7fffffffff |  0.5 TB | cpu_entry_area mapping
- fffffe8000000000 |   -1.5  TB | fffffeffffffffff |  0.5 TB | ... unused hole
- ffffff0000000000 |   -1    TB | ffffff7fffffffff |  0.5 TB | %esp fixup stacks
 __________________|____________|__________________|_________|____________________________________________________________
                                                             |
                                                             | Identical layout to the 47-bit one from here on:
 ____________________________________________________________|____________________________________________________________
                   |            |                  |         |
+ fffffc0000000000 |   -4    TB | fffffdffffffffff |    2 TB | ... unused hole
+                  |            |                  |         | vaddr_end for KASLR
+ fffffe0000000000 |   -2    TB | fffffe7fffffffff |  0.5 TB | cpu_entry_area mapping
+ fffffe8000000000 |   -1.5  TB | fffffeffffffffff |  0.5 TB | ... unused hole
+ ffffff0000000000 |   -1    TB | ffffff7fffffffff |  0.5 TB | %esp fixup stacks
  ffffff8000000000 | -512    GB | ffffffeeffffffff |  444 GB | ... unused hole
  ffffffef00000000 |  -68    GB | fffffffeffffffff |   64 GB | EFI region mapping space
  ffffffff00000000 |   -4    GB | ffffffff7fffffff |    2 GB | ... unused hole