[+Paolo, +Fam Zheng - for scsi]
+-- On Mon, 28 Sep 2020, P J P wrote --+ | +-- 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...? @Paolo, @Fam...wdyt? Thank you. -- Prasad J Pandit / Red Hat Product Security Team 8685 545E B54C 486B C6EB 271E E285 8B5A F050 DE8D