powerpc/8xx: fix handling of early NULL pointer dereference

NULL pointers are pointers to user memory space. So user pagetable
has to be set in order to avoid random behaviour in case of NULL
pointer dereference, otherwise we may encounter random memory
access hence Machine Check Exception from TLB Miss handlers.

Set user pagetable as early as possible in order to properly
catch early kernel NULL pointer dereference.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
index 6cab07e..04501b6 100644 (file)
--- a/arch/powerpc/kernel/head_8xx.S
+++ b/arch/powerpc/kernel/head_8xx.S
@@ -873,6 +873,10 @@ start_here:
        li      r0,0
        stwu    r0,THREAD_SIZE-STACK_FRAME_OVERHEAD(r1)
 
+       lis     r6, swapper_pg_dir@ha
+       tophys(r6,r6)
+       mtspr   SPRN_M_TW, r6
+
        bl      early_init      /* We have to do this with MMU on */
 
 /*
@@ -893,9 +897,6 @@ start_here:
         * init's THREAD like the context switch code does, but this is
         * easier......until someone changes init's static structures.
         */
-       lis     r6, swapper_pg_dir@ha
-       tophys(r6,r6)
-       mtspr   SPRN_M_TW, r6
        lis     r4,2f@h
        ori     r4,r4,2f@l
        tophys(r4,r4)