1 files changed, 228 insertions, 0 deletions
diff --git a/drivers/platform/surface/aggregator/ssh_parser.c b/drivers/platform/surface/aggregator/ssh_parser.c
new file mode 100644
index 000000000000..e2dead8de94a
--- /dev/null
+++ b/drivers/platform/surface/aggregator/ssh_parser.c
@@ -0,0 +1,228 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * SSH message parser.
+ *
+ * Copyright (C) 2019-2020 Maximilian Luz <luzmaximilian@gmail.com>
+ */
+
+#include <asm/unaligned.h>
+#include <linux/compiler.h>
+#include <linux/device.h>
+#include <linux/types.h>
+
+#include <linux/surface_aggregator/serial_hub.h>
+#include "ssh_parser.h"
+
+/**
+ * sshp_validate_crc() - Validate a CRC in raw message data.
+ * @src: The span of data over which the CRC should be computed.
+ * @crc: The pointer to the expected u16 CRC value.
+ *
+ * Computes the CRC of the provided data span (@src), compares it to the CRC
+ * stored at the given address (@crc), and returns the result of this
+ * comparison, i.e. %true if equal. This function is intended to run on raw
+ * input/message data.
+ *
+ * Return: Returns %true if the computed CRC matches the stored CRC, %false
+ * otherwise.
+ */
+static bool sshp_validate_crc(const struct ssam_span *src, const u8 *crc)
+{
+	u16 actual = ssh_crc(src->ptr, src->len);
+	u16 expected = get_unaligned_le16(crc);
+
+	return actual == expected;
+}
+
+/**
+ * sshp_starts_with_syn() - Check if the given data starts with SSH SYN bytes.
+ * @src: The data span to check the start of.
+ */
+static bool sshp_starts_with_syn(const struct ssam_span *src)
+{
+	return src->len >= 2 && get_unaligned_le16(src->ptr) == SSH_MSG_SYN;
+}
+
+/**
+ * sshp_find_syn() - Find SSH SYN bytes in the given data span.
+ * @src: The data span to search in.
+ * @rem: The span (output) indicating the remaining data, starting with SSH
+ *       SYN bytes, if found.
+ *
+ * Search for SSH SYN bytes in the given source span. If found, set the @rem
+ * span to the remaining data, starting with the first SYN bytes and capped by
+ * the source span length, and return %true. This function does not copy any
+ * data, but rather only sets pointers to the respective start addresses and
+ * length values.
+ *
+ * If no SSH SYN bytes could be found, set the @rem span to the zero-length
+ * span at the end of the source span and return %false.
+ *
+ * If partial SSH SYN bytes could be found at the end of the source span, set
+ * the @rem span to cover these partial SYN bytes, capped by the end of the
+ * source span, and return %false. This function should then be re-run once
+ * more data is available.
+ *
+ * Return: Returns %true if a complete SSH SYN sequence could be found,
+ * %false otherwise.
+ */
+bool sshp_find_syn(const struct ssam_span *src, struct ssam_span *rem)
+{
+	size_t i;
+
+	for (i = 0; i < src->len - 1; i++) {
+		if (likely(get_unaligned_le16(src->ptr + i) == SSH_MSG_SYN)) {
+			rem->ptr = src->ptr + i;
+			rem->len = src->len - i;
+			return true;
+		}
+	}
+
+	if (unlikely(src->ptr[src->len - 1] == (SSH_MSG_SYN & 0xff))) {
+		rem->ptr = src->ptr + src->len - 1;
+		rem->len = 1;
+		return false;
+	}
+
+	rem->ptr = src->ptr + src->len;
+	rem->len = 0;
+	return false;
+}
+
+/**
+ * sshp_parse_frame() - Parse SSH frame.
+ * @dev: The device used for logging.
+ * @source: The source to parse from.
+ * @frame: The parsed frame (output).
+ * @payload: The parsed payload (output).
+ * @maxlen: The maximum supported message length.
+ *
+ * Parses and validates a SSH frame, including its payload, from the given
+ * source. Sets the provided @frame pointer to the start of the frame and
+ * writes the limits of the frame payload to the provided @payload span
+ * pointer.
+ *
+ * This function does not copy any data, but rather only validates the message
+ * data and sets pointers (and length values) to indicate the respective parts.
+ *
+ * If no complete SSH frame could be found, the frame pointer will be set to
+ * the %NULL pointer and the payload span will be set to the null span (start
+ * pointer %NULL, size zero).
+ *
+ * Return: Returns zero on success or if the frame is incomplete, %-ENOMSG if
+ * the start of the message is invalid, %-EBADMSG if any (frame-header or
+ * payload) CRC is invalid, or %-EMSGSIZE if the SSH message is bigger than
+ * the maximum message length specified in the @maxlen parameter.
+ */
+int sshp_parse_frame(const struct device *dev, const struct ssam_span *source,
+		     struct ssh_frame **frame, struct ssam_span *payload,
+		     size_t maxlen)
+{
+	struct ssam_span sf;
+	struct ssam_span sp;
+
+	/* Initialize output. */
+	*frame = NULL;
+	payload->ptr = NULL;
+	payload->len = 0;
+
+	if (!sshp_starts_with_syn(source)) {
+		dev_warn(dev, "rx: parser: invalid start of frame\n");
+		return -ENOMSG;
+	}
+
+	/* Check for minimum packet length. */
+	if (unlikely(source->len < SSH_MESSAGE_LENGTH(0))) {
+		dev_dbg(dev, "rx: parser: not enough data for frame\n");
+		return 0;
+	}
+
+	/* Pin down frame. */
+	sf.ptr = source->ptr + sizeof(u16);
+	sf.len = sizeof(struct ssh_frame);
+
+	/* Validate frame CRC. */
+	if (unlikely(!sshp_validate_crc(&sf, sf.ptr + sf.len))) {
+		dev_warn(dev, "rx: parser: invalid frame CRC\n");
+		return -EBADMSG;
+	}
+
+	/* Ensure packet does not exceed maximum length. */
+	sp.len = get_unaligned_le16(&((struct ssh_frame *)sf.ptr)->len);
+	if (unlikely(SSH_MESSAGE_LENGTH(sp.len) > maxlen)) {
+		dev_warn(dev, "rx: parser: frame too large: %llu bytes\n",
+			 SSH_MESSAGE_LENGTH(sp.len));
+		return -EMSGSIZE;
+	}
+
+	/* Pin down payload. */
+	sp.ptr = sf.ptr + sf.len + sizeof(u16);
+
+	/* Check for frame + payload length. */
+	if (source->len < SSH_MESSAGE_LENGTH(sp.len)) {
+		dev_dbg(dev, "rx: parser: not enough data for payload\n");
+		return 0;
+	}
+
+	/* Validate payload CRC. */
+	if (unlikely(!sshp_validate_crc(&sp, sp.ptr + sp.len))) {
+		dev_warn(dev, "rx: parser: invalid payload CRC\n");
+		return -EBADMSG;
+	}
+
+	*frame = (struct ssh_frame *)sf.ptr;
+	*payload = sp;
+
+	dev_dbg(dev, "rx: parser: valid frame found (type: %#04x, len: %u)\n",
+		(*frame)->type, (*frame)->len);
+
+	return 0;
+}
+
+/**
+ * sshp_parse_command() - Parse SSH command frame payload.
+ * @dev: The device used for logging.
+ * @source: The source to parse from.
+ * @command: The parsed command (output).
+ * @command_data: The parsed command data/payload (output).
+ *
+ * Parses and validates a SSH command frame payload. Sets the @command pointer
+ * to the command header and the @command_data span to the command data (i.e.
+ * payload of the command). This will result in a zero-length span if the
+ * command does not have any associated data/payload. This function does not
+ * check the frame-payload-type field, which should be checked by the caller
+ * before calling this function.
+ *
+ * The @source parameter should be the complete frame payload, e.g. returned
+ * by the sshp_parse_frame() command.
+ *
+ * This function does not copy any data, but rather only validates the frame
+ * payload data and sets pointers (and length values) to indicate the
+ * respective parts.
+ *
+ * Return: Returns zero on success or %-ENOMSG if @source does not represent a
+ * valid command-type frame payload, i.e. is too short.
+ */
+int sshp_parse_command(const struct device *dev, const struct ssam_span *source,
+		       struct ssh_command **command,
+		       struct ssam_span *command_data)
+{
+	/* Check for minimum length. */
+	if (unlikely(source->len < sizeof(struct ssh_command))) {
+		*command = NULL;
+		command_data->ptr = NULL;
+		command_data->len = 0;
+
+		dev_err(dev, "rx: parser: command payload is too short\n");
+		return -ENOMSG;
+	}
+
+	*command = (struct ssh_command *)source->ptr;
+	command_data->ptr = source->ptr + sizeof(struct ssh_command);
+	command_data->len = source->len - sizeof(struct ssh_command);
+
+	dev_dbg(dev, "rx: parser: valid command found (tc: %#04x, cid: %#04x)\n",
+		(*command)->tc, (*command)->cid);
+
+	return 0;
+}