hw/misc/bcm2835_property: Fix handling of FRAMEBUFFER_SET_PALETTE

The documentation of the "Set palette" mailbox property at
https://github.com/raspberrypi/firmware/wiki/Mailbox-property-interface#set-palette
says it has the form:

    Length: 24..1032
    Value:
        u32: offset: first palette index to set (0-255)
        u32: length: number of palette entries to set (1-256)
        u32...: RGBA palette values (offset to offset+length-1)

We get this wrong in a couple of ways:
 * we aren't checking the offset and length are in range, so the guest
   can make us spin for a long time by providing a large length
 * the bounds check on our loop is wrong: we should iterate through
   'length' palette entries, not 'length - offset' entries

Fix the loop to implement the bounds checks and get the loop
condition right. In the process, make the variables local to
this switch case, rather than function-global, so it's clearer
what type they are when reading the code.

Cc: qemu-stable@nongnu.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20240723131029.1159908-2-peter.maydell@linaro.org
(cherry picked from commit 0892fffc2abaadfb5d8b79bb0250ae1794862560)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
(Mjt: context fix due to lack of
 v9.0.0-1812-g5d5f1b60916a "hw/misc: Implement mailbox properties for customer OTP and device specific private keys"
 v8.0.0-1924-g251918266666 "hw/misc/bcm2835_property: Use 'raspberrypi-fw-defs.h' definitions"
 also remove now-unused local `n' variable which gets removed in the next change in this file,
 v9.0.0-2720-g32f1c201eedf "hw/misc/bcm2835_property: Avoid overflow in OTP access properties")

1 files changed, 16 insertions, 11 deletions

diff --git a/hw/misc/bcm2835_property.c b/hw/misc/bcm2835_property.c
index de056ea2df..c7834d3fc7 100644
--- a/hw/misc/bcm2835_property.c
+++ b/hw/misc/bcm2835_property.c
@@ -26,8 +26,6 @@ static void bcm2835_property_mbox_push(BCM2835PropertyState *s, uint32_t value)
     uint32_t tot_len;
     size_t resplen;
     uint32_t tmp;
-    int n;
-    uint32_t offset, length, color;
 
     /*
      * Copy the current state of the framebuffer config; we will update
@@ -258,18 +256,25 @@ static void bcm2835_property_mbox_push(BCM2835PropertyState *s, uint32_t value)
             resplen = 16;
             break;
         case 0x0004800b: /* Set palette */
-            offset = ldl_le_phys(&s->dma_as, value + 12);
-            length = ldl_le_phys(&s->dma_as, value + 16);
-            n = 0;
-            while (n < length - offset) {
-                color = ldl_le_phys(&s->dma_as, value + 20 + (n << 2));
-                stl_le_phys(&s->dma_as,
-                            s->fbdev->vcram_base + ((offset + n) << 2), color);
-                n++;
+        {
+            uint32_t offset = ldl_le_phys(&s->dma_as, value + 12);
+            uint32_t length = ldl_le_phys(&s->dma_as, value + 16);
+            int resp;
+
+            if (offset > 255 || length < 1 || length > 256) {
+                resp = 1; /* invalid request */
+            } else {
+                for (uint32_t e = 0; e < length; e++) {
+                    uint32_t color = ldl_le_phys(&s->dma_as, value + 20 + (e << 2));
+                    stl_le_phys(&s->dma_as,
+                                s->fbdev->vcram_base + ((offset + e) << 2), color);
+                }
+                resp = 0;
             }
-            stl_le_phys(&s->dma_as, value + 12, 0);
+            stl_le_phys(&s->dma_as, value + 12, resp);
             resplen = 4;
             break;
+        }
         case 0x00040013: /* Get number of displays */
             stl_le_phys(&s->dma_as, value + 12, 1);
             resplen = 4;