powerpc/mm: Prevent unlikely crash in copro_calculate_slb()

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")
Cc: stable@vger.kernel.org # v3.18+
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>

diff --git a/arch/powerpc/mm/copro_fault.c b/arch/powerpc/mm/copro_fault.c
index bb0354222b1158c57133a09ef50b98cf20de6f29..362954f98029b46d4d3d312b239bb7a2fa8fe63a 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);