FROMLIST: rpmsg: glink: smem: validate index before fifo read write

Fifo head and tail index can be modified with wrong values from
untrusted remote procs. Glink smem is not validating these index
before using to read or write fifo. This can result in out of
bound memory access if head and tail have incorrect values.

Add check for validation of head and tail index. This check will
put index within fifo boundaries, so that no invalid memory access
is made. Further this may result in certain packet drops unless
glink finds a valid packet header in fifo again and recovers.

Crash signature and calltrace with wrong head and tail values:

Internal error: Oops: 96000007 [#1] PREEMPT SMP
pc : __memcpy_fromio+0x34/0xb4
lr : glink_smem_rx_peak+0x68/0x94

__memcpy_fromio+0x34/0xb4
glink_smem_rx_peak+0x68/0x94
qcom_glink_native_intr+0x90/0x888

Link: https://lore.kernel.org/r/20231201110631.669085-1-quic_deesin@quicinc.com
Signed-off-by: Deepak Kumar Singh <quic_deesin@quicinc.com>

Author: quic-deesin

drivers/rpmsg/qcom_glink_smem.c

@@ -86,9 +86,14 @@ static size_t glink_smem_rx_avail(struct qcom_glink_pipe *np)
 	tail = le32_to_cpu(*pipe->tail);
 
 	if (head < tail)
-		return pipe->native.length - tail + head;
+		len = pipe->native.length - tail + head;
 	else
-		return head - tail;
+		len = head - tail;
+
+	if (WARN_ON_ONCE(len > pipe->native.length))
+		len = 0;
+
+	return len;
 }
 
 static void glink_smem_rx_peek(struct qcom_glink_pipe *np,
@@ -99,6 +104,10 @@ static void glink_smem_rx_peek(struct qcom_glink_pipe *np,
 	u32 tail;
 
 	tail = le32_to_cpu(*pipe->tail);
+
+	if (WARN_ON_ONCE(tail > pipe->native.length))
+		return;
+
 	tail += offset;
 	if (tail >= pipe->native.length)
 		tail -= pipe->native.length;
@@ -121,7 +130,7 @@ static void glink_smem_rx_advance(struct qcom_glink_pipe *np,
 
 	tail += count;
 	if (tail >= pipe->native.length)
-		tail -= pipe->native.length;
+		tail %= pipe->native.length;
 
 	*pipe->tail = cpu_to_le32(tail);
 }
@@ -146,6 +155,9 @@ static size_t glink_smem_tx_avail(struct qcom_glink_pipe *np)
 	else
 		avail -= FIFO_FULL_RESERVE + TX_BLOCKED_CMD_RESERVE;
 
+	if (WARN_ON_ONCE(avail > pipe->native.length))
+		avail = 0;
+
 	return avail;
 }
 
@@ -155,6 +167,9 @@ static unsigned int glink_smem_tx_write_one(struct glink_smem_pipe *pipe,
 {
 	size_t len;
 
+	if (WARN_ON_ONCE(head > pipe->native.length))
+		return head;
+
 	len = min_t(size_t, count, pipe->native.length - head);
 	if (len)
 		memcpy(pipe->fifo + head, data, len);