powerpc/mm: Prevent unlikely crash in copro_calculate_slb()

commit d2cf909cda5f8c5609cb7ed6cda816c3e15528c7 upstream.

If a cxl adapter faults on an invalid address for a kernel context, we
may enter copro_calculate_slb() with a NULL mm pointer (kernel
context) and an effective address which looks like a user
address. Which will cause a crash when dereferencing mm. It is clearly
an AFU bug, but there's no reason to crash either. So return an error,
so that cxl can ack the interrupt with an address error.

Fixes: 73d16a6e0e51 ("powerpc/cell: Move data segment faulting code out of cell platform")
Signed-off-by: Frederic Barrat <fbarrat@linux.vnet.ibm.com>
Acked-by: Ian Munsie <imunsie@au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/powerpc/mm/copro_fault.c b/arch/powerpc/mm/copro_fault.c
index 6527882ce05ede3a0a45f74d3a11c4c375da6514..ddfd2740a1b5d3cd643207fd5250a3515e810987 100644 (file)
--- a/arch/powerpc/mm/copro_fault.c
+++ b/arch/powerpc/mm/copro_fault.c
@@ -106,6 +106,8 @@ int copro_calculate_slb(struct mm_struct *mm, u64 ea, struct copro_slb *slb)
        switch (REGION_ID(ea)) {
        case USER_REGION_ID:
                pr_devel("%s: 0x%llx -- USER_REGION_ID\n", __func__, ea);
+               if (mm == NULL)
+                       return 1;
                psize = get_slice_psize(mm, ea);
                ssize = user_segment_size(ea);
                vsid = get_vsid(mm->context.id, ea, ssize);