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Re: [PATCH] pci: check bus pointer before dereference
From: |
Michael S. Tsirkin |
Subject: |
Re: [PATCH] pci: check bus pointer before dereference |
Date: |
Fri, 30 Oct 2020 05:01:23 -0400 |
On Wed, Sep 30, 2020 at 10:32:42AM +0530, P J P wrote:
>
> [+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 <ppandit@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.
Guys are we going anywhere with this patch?
> --
> Prasad J Pandit / Red Hat Product Security Team
> 8685 545E B54C 486B C6EB 271E E285 8B5A F050 DE8D
- Re: [PATCH] pci: check bus pointer before dereference,
Michael S. Tsirkin <=