Hello, +-- On Wed, 16 Sep 2020, Peter Maydell wrote --+ | On Wed, 16 Sep 2020 at 07:28, P J P <ppan...@redhat.com> wrote: | > -> https://ruhr-uni-bochum.sciebo.de/s/NNWP2GfwzYKeKwE?path=%2Flsi_nullptr1 | > ==1183858==Hint: address points to the zero page. | > #0 pci_change_irq_level hw/pci/pci.c:259 | > #1 pci_irq_handler hw/pci/pci.c:1445 | > #2 pci_set_irq hw/pci/pci.c:1463 | > #3 lsi_set_irq hw/scsi/lsi53c895a.c:488 | > #4 lsi_update_irq hw/scsi/lsi53c895a.c:523 | > #5 lsi_script_scsi_interrupt hw/scsi/lsi53c895a.c:554 | > #6 lsi_execute_script hw/scsi/lsi53c895a.c:1149 | > #7 lsi_reg_writeb hw/scsi/lsi53c895a.c:1984 | > #8 lsi_io_write hw/scsi/lsi53c895a.c:2146 ... | Generally we don't bother to assert() that pointers that shouldn't be NULL | really are NULL immediately before dereferencing them, because the | dereference provides an equally easy-to-debug crash to the assert, and so | the assert doesn't provide anything extra. assert()ing that a pointer is | non-NULL is more useful if it is done in a place that identifies the problem | at an earlier and easier-to-debug point in execution rather than at a later | point which is distantly removed from the place where the bogus pointer was | introduced.
* The NULL dereference above occurs because the 'pci_dev->qdev->parent_bus' address gets overwritten (with 0x0) during scsi 'Memory Move' operation in ../hw/scsi/lsi53c895a.c #define LSI_BUF_SIZE 4096 lsi_mmio_write lsi_reg_writeb lsi_execute_script static void lsi_memcpy(LSIState *s, ... int count=12MB) { int n; uint8_t buf[LSI_BUF_SIZE]; while (count) { n = (count > LSI_BUF_SIZE) ? LSI_BUF_SIZE : count; lsi_mem_read(s, src, buf, n); <== read from DMA memory lsi_mem_write(s, dest, buf, n); <== write to I/O memory src += n; dest += n; count -= n; } } -> https://www.manualslib.com/manual/1407578/Lsi-Lsi53c895a.html?page=254#manual * Above loop moves data between DMA memory to i/o address space. * Going through the manual above, it seems 'Memory Move' can move upto 16MB of data between memory spaces. * I tried to see a suitable fix, but couldn't get one. - Limiting 'count' value does not seem right, as allowed value is upto 16MB. - Manual above talks about moving data via 'dma_buf'. But it doesn't seem to be used here. * During above loop, 'dest' address moves past its 'MemoryRegion mr' and overwrites the adjacent 'mr' memory area, overwritting 'parent_bus' value. Any thoughts/hints please...? Thank you. -- Prasad J Pandit / Red Hat Product Security Team 8685 545E B54C 486B C6EB 271E E285 8B5A F050 DE8D