Re: [Qemu-devel] [PATCH v1] arm: check bit index before usage

[P J P]

+-- On Thu, 25 Oct 2018, Peter Maydell wrote --+
| Hi; thanks for this patch. Looking at the SA1110 manual,
| it says that writes to the reserved bits [31:28] are
| ignored. So I think that rather than doing this check
| here, we should do what the strongarm_ppc_* code in the
| same file does -- mask off the high bits for writes to
| the direction and state registers. Then it will not
| be possible for high bits to be set here that cause an
| out-of-range array access.

===
diff --git a/hw/arm/strongarm.c b/hw/arm/strongarm.c
index ec2627374d..dd8c4b1f2e 100644
--- a/hw/arm/strongarm.c
+++ b/hw/arm/strongarm.c
@@ -587,12 +587,12 @@ static void strongarm_gpio_write(void *opaque, hwaddr 
offset,
 
     switch (offset) {
     case GPDR:        /* GPIO Pin-Direction registers */
-        s->dir = value;
+        s->dir = value & 0x3fffff;
         strongarm_gpio_handler_update(s);
         break;
 
     case GPSR:        /* GPIO Pin-Output Set registers */
-        s->olevel |= value;
+        s->olevel |= value & 0x3fffff;
         strongarm_gpio_handler_update(s);
         break;
===

does this seem okay?
 
| Side note: this device is used only in the "collie"
| machine model, which only works via TCG, so this is
| not a security issue, just a bug (which will only be
| visible if the guest is buggy.)

Cool, thank you.
--
Prasad J Pandit / Red Hat Product Security Team
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