powerpc/64s/radix: Boot-time NULL pointer protection using a guard-PID

[mirror_ubuntu-bionic-kernel.git] / arch / powerpc / mm / pgtable-radix.c

diff --git a/arch/powerpc/mm/pgtable-radix.c b/arch/powerpc/mm/pgtable-radix.c
index 17ae5c15a9e066329c0d2c338eac5d3076ea7e41..804ba030d859857625d26dd1a294a360a5a39b24 100644 (file)
--- a/arch/powerpc/mm/pgtable-radix.c
+++ b/arch/powerpc/mm/pgtable-radix.c
@@ -21,6 +21,7 @@
 
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
+#include <asm/mmu_context.h>
 #include <asm/dma.h>
 #include <asm/machdep.h>
 #include <asm/mmu.h>
@@ -334,6 +335,22 @@ static void __init radix_init_pgtable(void)
                     "r" (TLBIEL_INVAL_SET_LPID), "r" (0));
        asm volatile("eieio; tlbsync; ptesync" : : : "memory");
        trace_tlbie(0, 0, TLBIEL_INVAL_SET_LPID, 0, 2, 1, 1);
+
+       /*
+        * The init_mm context is given the first available (non-zero) PID,
+        * which is the "guard PID" and contains no page table. PIDR should
+        * never be set to zero because that duplicates the kernel address
+        * space at the 0x0... offset (quadrant 0)!
+        *
+        * An arbitrary PID that may later be allocated by the PID allocator
+        * for userspace processes must not be used either, because that
+        * would cause stale user mappings for that PID on CPUs outside of
+        * the TLB invalidation scheme (because it won't be in mm_cpumask).
+        *
+        * So permanently carve out one PID for the purpose of a guard PID.
+        */
+       init_mm.context.id = mmu_base_pid;
+       mmu_base_pid++;
 }
 
 static void __init radix_init_partition_table(void)
@@ -580,6 +597,8 @@ void __init radix__early_init_mmu(void)
 
        radix_init_iamr();
        radix_init_pgtable();
+       /* Switch to the guard PID before turning on MMU */
+       radix__switch_mmu_context(NULL, &init_mm);
 }
 
 void radix__early_init_mmu_secondary(void)
@@ -601,6 +620,7 @@ void radix__early_init_mmu_secondary(void)
                radix_init_amor();
        }
        radix_init_iamr();
+       radix__switch_mmu_context(NULL, &init_mm);
 }
 
 void radix__mmu_cleanup_all(void)