Commit 6f20e7f2 authored Jan 08, 2015 by Gavin Shan Committed by Michael Ellerman Jan 23, 2015

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: 6f4441ef ("powerpc: Dynamically allocate slb_shadow from memblock")
Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

parent 53a448c3

arch/powerpc/kernel/paca.c

+8 −0

Original line number	Diff line number	Diff line
		@@ -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));