QEMU: aarch64: :GIC: out-of-bounds access via interrupt ID

Via [qemu-security] list

+-- On Sun, 31 Jan 2021, Philippe Mathieu-Daudé wrote --+
| On 1/31/21 11:34 AM, Philippe Mathieu-Daudé wrote:
| > Per the ARM Generic Interrupt Controller Architecture specification
| > (document "ARM IHI 0048B.b (ID072613)"), the SGIINTID field is 4 bit,
| > not 10:
| >
| >    - Table 4-21 GICD_SGIR bit assignments
| >
| >    The Interrupt ID of the SGI to forward to the specified CPU
| >    interfaces. The value of this field is the Interrupt ID, in
| >    the range 0-15, for example a value of 0b0011 specifies
| >    Interrupt ID 3.
| >
...
| > Correct the irq mask to fix an undefined behavior (which eventually
| > lead to a heap-buffer-overflow, see [Buglink]):
| >
| >    $ echo 'writel 0x8000f00 0xff4affb0' | qemu-system-aarch64 -M virt,accel=qtest -qtest stdio
| >    [I 1612088147.116987] OPENED
| >  [R +0.278293] writel 0x8000f00 0xff4affb0
| >  ../hw/intc/arm_gic.c:1498:13: runtime error: index 944 out of bounds for type 'uint8_t [16][8]'
| >  SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior ../hw/intc/arm_gic.c:1498:13
| >
| > Cc: <email address hidden>
| > Fixes: 9ee6e8bb853 ("ARMv7 support.")
| > Buglink: https://bugs.launchpad.net/qemu/+bug/1913916
| > Buglink: https://bugs.launchpad.net/qemu/+bug/1913917
...

On 210202 1221, Peter Maydell wrote:
> In both cases the overrun is on the first writel to 0x8000f00,
> but the fuzzer has for some reason not reported that but instead
> blundered on until it happens to trigger some other issue that
> resulted from the memory corruption it induced with the first write.
>
...
> On the CVE:
>
> Since this can affect systems using KVM, this is a security bug for
> us. However, it only affects an uncommon configuration:
> you are only vulnerable if you are using "kernel-irqchip=off"
> (the default is 'on', and turning it off is an odd thing to do).
>
> thanks
> -- PMM
>