powerpc/32: Fix hardlockup on vmap stack overflow

Since the commit c118c7303ad5 ("powerpc/32: Fix vmap stack - Do not
activate MMU before reading task struct") a vmap stack overflow
results in a hard lockup. This is because emergency_ctx is still
addressed with its virtual address allthough data MMU is not active
anymore at that time.

Fix it by using a physical address instead.

Fixes: c118c7303ad5 ("powerpc/32: Fix vmap stack - Do not activate MMU before reading task struct")
Cc: stable@vger.kernel.org # v5.10+
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/ce30364fb7ccda489272af4a1612b6aa147e1d23.1637227521.git.christophe.leroy@csgroup.eu

diff --git a/arch/powerpc/kernel/head_32.h b/arch/powerpc/kernel/head_32.h
index 6b1ec9e3541b9046ac0a81198ac3598d21f7c294..349c4a820231bd2ecc21baed8ae9a1721acd351e 100644 (file)
--- a/arch/powerpc/kernel/head_32.h
+++ b/arch/powerpc/kernel/head_32.h
@@ -202,11 +202,11 @@ vmap_stack_overflow:
        mfspr   r1, SPRN_SPRG_THREAD
        lwz     r1, TASK_CPU - THREAD(r1)
        slwi    r1, r1, 3
-       addis   r1, r1, emergency_ctx@ha
+       addis   r1, r1, emergency_ctx-PAGE_OFFSET@ha
 #else
-       lis     r1, emergency_ctx@ha
+       lis     r1, emergency_ctx-PAGE_OFFSET@ha
 #endif
-       lwz     r1, emergency_ctx@l(r1)
+       lwz     r1, emergency_ctx-PAGE_OFFSET@l(r1)
        addi    r1, r1, THREAD_SIZE - INT_FRAME_SIZE
        EXCEPTION_PROLOG_2 0 vmap_stack_overflow
        prepare_transfer_to_handler