Re: [PATCH v2] hw/pci-host/q35: Ignore write of reserved PCIEXBAR LENGTH field

[Alexander Bulekov]

On 210526 1624, Philippe Mathieu-Daudé wrote:
> libFuzzer triggered the following assertion:
> 
>   cat << EOF | qemu-system-i386 -M pc-q35-5.0 \
>     -nographic -monitor none -serial none \
>     -qtest stdio -d guest_errors -trace pci\*
>   outl 0xcf8 0xf2000060
>   outl 0xcfc 0x8400056e
>   EOF
>   pci_cfg_write mch 00:0 @0x60 <- 0x8400056e
>   Aborted (core dumped)
> 
> This is because guest wrote MCH_HOST_BRIDGE_PCIEXBAR_LENGTH_RVD
> (reserved value) to the PCIE XBAR register.
> 
> There is no indication on the datasheet about what occurs when
> this value is written. Simply ignore it on QEMU (and report an
> guest error):
> 
>   pci_cfg_write mch 00:0 @0x60 <- 0x8400056e
>   Q35: Reserved PCIEXBAR LENGTH
>   pci_cfg_read mch 00:0 @0x0 -> 0x8086
>   pci_cfg_read mch 00:0 @0x0 -> 0x29c08086
>   ...
> 
> Cc: qemu-stable@nongnu.org
> Reported-by: Alexander Bulekov <alxndr@bu.edu>
> BugLink: https://bugs.launchpad.net/qemu/+bug/1878641
> Fixes: df2d8b3ed4 ("q35: Introduce q35 pc based chipset emulator")
> Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> ---

Reviewed-by: Alexander Bulekov <alxndr@bu.edu>