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[PATCH v2 1/2] ait-vga: check address before reading configuration bytes

From: P J P
Subject: [PATCH v2 1/2] ait-vga: check address before reading configuration bytes
Date: Thu, 4 Jun 2020 01:52:50 +0530

From: Prasad J Pandit <pjp@fedoraproject.org>

While reading PCI configuration bytes, a guest may send an
address towards the end of the configuration space. It may lead
to an OOB access issue. Add check to ensure 'address + size' is
within PCI configuration space.

Reported-by: Ren Ding <rding@gatech.edu>
Reported-by: Hanqing Zhao <hanqing@gatech.edu>
Reported-by: Yi Ren <c4tren@gmail.com>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
 hw/display/ati.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

Update v2: add check to avoid OOB PCI configuration space access
  -> https://lists.gnu.org/archive/html/qemu-devel/2020-06/msg00711.html

diff --git a/hw/display/ati.c b/hw/display/ati.c
index bda4a2d816..6671959e5d 100644
--- a/hw/display/ati.c
+++ b/hw/display/ati.c
@@ -384,7 +384,10 @@ static uint64_t ati_mm_read(void *opaque, hwaddr addr, 
unsigned int size)
         val = s->regs.crtc_pitch;
     case 0xf00 ... 0xfff:
-        val = pci_default_read_config(&s->dev, addr - 0xf00, size);
+        addr = addr - 0xf00;
+        if (addr + size <= 0xff) {
+            val = pci_default_read_config(&s->dev, addr, size);
+        }
     case CUR_OFFSET:
         val = s->regs.cur_offset;

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