[PATCH] hw/intc/arm_gic: Fix interrupt ID in GICD_SGIR register

[Philippe Mathieu-Daudé]

Per the ARM Generic Interrupt Controller Architecture specification
(document "ARM IHI 0048B.b (ID072613)"), the SGIINTID field is 4 bit,
not 10:

  - 4.3 Distributor register descriptions
  - 4.3.15 Software Generated Interrupt Register, GICD_SG

    - 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: qemu-stable@nongnu.org
Fixes: 9ee6e8bb853 ("ARMv7 support.")
Buglink: https://bugs.launchpad.net/qemu/+bug/1913916
Reported-by: Alexander Bulekov <alxndr@bu.edu>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
---
Isnt it worth a CVE to help distributions track backports?
---
 hw/intc/arm_gic.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/intc/arm_gic.c b/hw/intc/arm_gic.c
index af41e2fb448..75316329516 100644
--- a/hw/intc/arm_gic.c
+++ b/hw/intc/arm_gic.c
@@ -1476,7 +1476,7 @@ static void gic_dist_writel(void *opaque, hwaddr offset,
         int target_cpu;
 
         cpu = gic_get_current_cpu(s);
-        irq = value & 0x3ff;
+        irq = value & 0xf;
         switch ((value >> 24) & 3) {
         case 0:
             mask = (value >> 16) & ALL_CPU_MASK;
-- 
2.26.2