From 6f20e7f2e930211613a66d0603fa4abaaf3ce662 Mon Sep 17 00:00:00 2001 From: Gavin Shan Date: Thu, 8 Jan 2015 16:40:51 +1100 Subject: [PATCH] powerpc/kernel: Avoid memory corruption at early stage When calling to early_setup(), we pick "boot_paca" up for the master CPU and initialize that with initialise_paca(). At that point, the SLB shadow buffer isn't populated yet. Updating the SLB shadow buffer should corrupt what we had in physical address 0 where the trap instruction is usually stored. This hasn't been observed to cause any trouble in practice, but is obviously fishy. Fixes: 6f4441ef7009 ("powerpc: Dynamically allocate slb_shadow from memblock") Signed-off-by: Gavin Shan Signed-off-by: Michael Ellerman --- arch/powerpc/kernel/paca.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/arch/powerpc/kernel/paca.c b/arch/powerpc/kernel/paca.c index d6e195e8cd4c..5a23b69f8129 100644 --- a/arch/powerpc/kernel/paca.c +++ b/arch/powerpc/kernel/paca.c @@ -115,6 +115,14 @@ static struct slb_shadow * __init init_slb_shadow(int cpu) { struct slb_shadow *s = &slb_shadow[cpu]; + /* + * When we come through here to initialise boot_paca, the slb_shadow + * buffers are not allocated yet. That's OK, we'll get one later in + * boot, but make sure we don't corrupt memory at 0. + */ + if (!slb_shadow) + return NULL; + s->persistent = cpu_to_be32(SLB_NUM_BOLTED); s->buffer_length = cpu_to_be32(sizeof(*s)); -- 2.20.1