On 14/03/2023 18.08, Peter Maydell wrote:
The cadence UART attempts to avoid allowing the guset to set invalid
baud rate register values in the uart_write() function. However it
does the "mask to the size of the register field" and "check for
invalid values" in the wrong order, which means that a malicious
guest can get a bogus value into the register by setting also some
high bits in the value, and cause QEMU to crash by division-by-zero.
Do the mask before the bounds check instead of afterwards.
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1493
Signed-off-by: Peter Maydell <peter.mayd...@linaro.org>
---
hw/char/cadence_uart.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/hw/char/cadence_uart.c b/hw/char/cadence_uart.c
index c069a30842e..807e3985419 100644
--- a/hw/char/cadence_uart.c
+++ b/hw/char/cadence_uart.c
@@ -450,13 +450,15 @@ static MemTxResult uart_write(void *opaque, hwaddr offset,
}
break;
case R_BRGR: /* Baud rate generator */
+ value &= 0xffff;
if (value >= 0x01) {
- s->r[offset] = value & 0xFFFF;
+ s->r[offset] = value;
}
break;
case R_BDIV: /* Baud rate divider */
+ value &= 0xff;
if (value >= 0x04) {
- s->r[offset] = value & 0xFF;
+ s->r[offset] = value;
}
break;
default:
Reviewed-by: Thomas Huth <th...@redhat.com>