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Subject[PATCH] powerpc/8xx: fix handling of early NULL pointer dereference
Date
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>
---
arch/powerpc/kernel/head_8xx.S | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
index 6cab07e76732..04501b65040e 100644
--- 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)
--
2.13.3
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