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Re: [PATCH] pci: check bus pointer before dereference
From: |
P J P |
Subject: |
Re: [PATCH] pci: check bus pointer before dereference |
Date: |
Mon, 28 Sep 2020 16:33:48 +0530 (IST) |
Hello,
+-- 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...?
Thank you.
--
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, P J P, 2020/09/15
- Re: [PATCH] pci: check bus pointer before dereference, Li Qiang, 2020/09/15
- Re: [PATCH] pci: check bus pointer before dereference, Philippe Mathieu-Daudé, 2020/09/15
- Re: [PATCH] pci: check bus pointer before dereference, P J P, 2020/09/16
- Re: [PATCH] pci: check bus pointer before dereference, Peter Maydell, 2020/09/16
- Re: [PATCH] pci: check bus pointer before dereference,
P J P <=
- Re: [PATCH] pci: check bus pointer before dereference, P J P, 2020/09/30
- Re: [PATCH] pci: check bus pointer before dereference, Igor Mammedov, 2020/09/30
- Re: [PATCH] pci: check bus pointer before dereference, P J P, 2020/09/30