powerpc/powernv: Fix fortify source warnings in opal-prd.c

As reported by Mahesh & Aneesh, opal_prd_msg_notifier() triggers a
FORTIFY_SOURCE warning:

  memcpy: detected field-spanning write (size 32) of single field "&item->msg" at arch/powerpc/platforms/powernv/opal-prd.c:355 (size 4)
  WARNING: CPU: 9 PID: 660 at arch/powerpc/platforms/powernv/opal-prd.c:355 opal_prd_msg_notifier+0x174/0x188 [opal_prd]
  NIP opal_prd_msg_notifier+0x174/0x188 [opal_prd]
  LR  opal_prd_msg_notifier+0x170/0x188 [opal_prd]
  Call Trace:
    opal_prd_msg_notifier+0x170/0x188 [opal_prd] (unreliable)
    notifier_call_chain+0xc0/0x1b0
    atomic_notifier_call_chain+0x2c/0x40
    opal_message_notify+0xf4/0x2c0

This happens because the copy is targeting item->msg, which is only 4
bytes in size, even though the enclosing item was allocated with extra
space following the msg.

To fix the warning define struct opal_prd_msg with a union of the header
and a flex array, and have the memcpy target the flex array.

Reported-by: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Reported-by: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Tested-by: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Reviewed-by: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230821142820.497107-1-mpe@ellerman.id.au

diff --git a/arch/powerpc/platforms/powernv/opal-prd.c b/arch/powerpc/platforms/powernv/opal-prd.c
index 113bdb151f6873e4c970abed30c2e6d1315950c7..40e26e9f318fda81b90ae61305adb8b5d2d46da7 100644 (file)
--- a/arch/powerpc/platforms/powernv/opal-prd.c
+++ b/arch/powerpc/platforms/powernv/opal-prd.c
@@ -24,13 +24,20 @@
 #include <linux/uaccess.h>
 
 
+struct opal_prd_msg {
+       union {
+               struct opal_prd_msg_header header;
+               DECLARE_FLEX_ARRAY(u8, data);
+       };
+};
+
 /*
  * The msg member must be at the end of the struct, as it's followed by the
  * message data.
  */
 struct opal_prd_msg_queue_item {
-       struct list_head                list;
-       struct opal_prd_msg_header      msg;
+       struct list_head        list;
+       struct opal_prd_msg     msg;
 };
 
 static struct device_node *prd_node;
@@ -156,7 +163,7 @@ static ssize_t opal_prd_read(struct file *file, char __user *buf,
        int rc;
 
        /* we need at least a header's worth of data */
-       if (count < sizeof(item->msg))
+       if (count < sizeof(item->msg.header))
                return -EINVAL;
 
        if (*ppos)
@@ -186,7 +193,7 @@ static ssize_t opal_prd_read(struct file *file, char __user *buf,
                        return -EINTR;
        }
 
-       size = be16_to_cpu(item->msg.size);
+       size = be16_to_cpu(item->msg.header.size);
        if (size > count) {
                err = -EINVAL;
                goto err_requeue;
@@ -352,7 +359,7 @@ static int opal_prd_msg_notifier(struct notifier_block *nb,
        if (!item)
                return -ENOMEM;
 
-       memcpy(&item->msg, msg->params, msg_size);
+       memcpy(&item->msg.data, msg->params, msg_size);
 
        spin_lock_irqsave(&opal_prd_msg_queue_lock, flags);
        list_add_tail(&item->list, &opal_prd_msg_queue);