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spapr: Fix undefined behaviour in spapr_tce_reset() 

When a TCE table (sPAPR IOMMU context) is in disabled state (which is true
by default for the 64-bit window), it has tcet->nb_table == 0 and
tcet->table == NULL.  However, on system reset, spapr_tce_reset() executes,
which unconditionally calls
        memset(tcet->table, 0, table_size);

We get away with this in practice, because it's a zero length memset(),
but memset() on a NULL pointer is undefined behaviour, so we should not
call it in this case.

Reported-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
This commit is contained in:
David Gibson 2016-08-08 10:06:25 +10:00
parent 16275edb34
commit 57c0eb1e0d
1 changed files with 3 additions and 1 deletions
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4
hw/ppc/spapr_iommu.c
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@ -385,7 +385,9 @@ static void spapr_tce_reset(DeviceState *dev)
sPAPRTCETable *tcet = SPAPR_TCE_TABLE(dev);
size_t table_size = tcet->nb_table * sizeof(uint64_t);
memset(tcet->table, 0, table_size);
if (tcet->nb_table) {
memset(tcet->table, 0, table_size);
}
}
static target_ulong put_tce_emu(sPAPRTCETable *tcet, target_ulong ioba,