[PATCH v2 2/9] hw/i2c: pmbus: guard against out of range accesses

[Titus Rwantare]

Signed-off-by: Titus Rwantare <titusr@google.com>
---
 hw/i2c/pmbus_device.c | 41 ++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 40 insertions(+), 1 deletion(-)

diff --git a/hw/i2c/pmbus_device.c b/hw/i2c/pmbus_device.c
index 07a45c99f9..93c746bab3 100644
--- a/hw/i2c/pmbus_device.c
+++ b/hw/i2c/pmbus_device.c
@@ -243,18 +243,47 @@ void pmbus_check_limits(PMBusDevice *pmdev)
     }
 }
 
+/* assert the status_cml error upon receipt of malformed command */
+static void pmbus_cml_error(PMBusDevice *pmdev)
+{
+    for (int i = 0; i < pmdev->num_pages; i++) {
+        pmdev->pages[i].status_word |= PMBUS_STATUS_CML;
+        pmdev->pages[i].status_cml |= PB_CML_FAULT_INVALID_CMD;
+    }
+}
+
 static uint8_t pmbus_receive_byte(SMBusDevice *smd)
 {
     PMBusDevice *pmdev = PMBUS_DEVICE(smd);
     PMBusDeviceClass *pmdc = PMBUS_DEVICE_GET_CLASS(pmdev);
     uint8_t ret = 0xFF;
-    uint8_t index = pmdev->page;
+    uint8_t index;
 
     if (pmdev->out_buf_len != 0) {
         ret = pmbus_out_buf_pop(pmdev);
         return ret;
     }
 
+    /*
+     * Reading from all pages will return the value from page 0,
+     * this is unspecified behaviour in general.
+     */
+    if (pmdev->page == PB_ALL_PAGES) {
+        index = 0;
+        qemu_log_mask(LOG_GUEST_ERROR,
+                      "%s: tried to read from all pages\n",
+                      __func__);
+        pmbus_cml_error(pmdev);
+    } else if (pmdev->page > pmdev->num_pages - 1) {
+        qemu_log_mask(LOG_GUEST_ERROR,
+                      "%s: page %d is out of range\n",
+                      __func__, pmdev->page);
+        pmbus_cml_error(pmdev);
+        return -1;
+    } else {
+        index = pmdev->page;
+    }
+
     switch (pmdev->code) {
     case PMBUS_PAGE:
         pmbus_send8(pmdev, pmdev->page);
@@ -1038,6 +1067,7 @@ static int pmbus_write_data(SMBusDevice *smd, uint8_t 
*buf, uint8_t len)
         pmdev->page = pmbus_receive8(pmdev);
         return 0;
     }
+
     /* loop through all the pages when 0xFF is received */
     if (pmdev->page == PB_ALL_PAGES) {
         for (int i = 0; i < pmdev->num_pages; i++) {
@@ -1048,6 +1078,15 @@ static int pmbus_write_data(SMBusDevice *smd, uint8_t 
*buf, uint8_t len)
         return 0;
     }
 
+    if (pmdev->page > pmdev->num_pages - 1) {
+        qemu_log_mask(LOG_GUEST_ERROR,
+                        "%s: page %u is out of range\n",
+                        __func__, pmdev->page);
+        pmdev->page = 0; /* undefined behaviour - reset to page 0 */
+        pmbus_cml_error(pmdev);
+        return -1;
+    }
+
     index = pmdev->page;
 
     switch (pmdev->code) {
-- 
2.35.1.616.g0bdcbb4464-goog