[PATCH v3 5/6] tpm: Add tpm_buf_read_{u8,u16,u32}

[Jarkko Sakkinen]

Add tpm_buf_read_u8(), tpm_buf_read_u16() and tpm_read_u32() for the sake
of more convenient parsing of TPM responses.

Signed-off-by: Jarkko Sakkinen <jar...@kernel.org>
---
 drivers/char/tpm/tpm-buf.c | 69 ++++++++++++++++++++++++++++++++++++++
 include/linux/tpm.h        |  3 ++
 2 files changed, 72 insertions(+)

diff --git a/drivers/char/tpm/tpm-buf.c b/drivers/char/tpm/tpm-buf.c
index f1d92d7e758d..bcd3cbcd9dd9 100644
--- a/drivers/char/tpm/tpm-buf.c
+++ b/drivers/char/tpm/tpm-buf.c
@@ -124,3 +124,72 @@ void tpm_buf_append_u32(struct tpm_buf *buf, const u32 
value)
        tpm_buf_append(buf, (u8 *)&value2, 4);
 }
 EXPORT_SYMBOL_GPL(tpm_buf_append_u32);
+
+/**
+ * tpm_buf_read() - Read from a TPM buffer
+ * @buf:       &tpm_buf instance
+ * @offset:    offset within the buffer
+ * @count:     the number of bytes to read
+ * @output:    the output buffer
+ */
+static void tpm_buf_read(const struct tpm_buf *buf, off_t *offset, size_t 
count, void *output)
+{
+       if (*(offset + count) >= buf->length) {
+               WARN(1, "tpm_buf: overflow\n");
+               return;
+       }
+
+       memcpy(output, &buf->data[*offset], count);
+       *offset += count;
+}
+
+/**
+ * tpm_buf_read_u8() - Read 8-bit word from a TPM buffer
+ * @buf:       &tpm_buf instance
+ * @offset:    offset within the buffer
+ *
+ * Return: next 8-bit word
+ */
+u8 tpm_buf_read_u8(const struct tpm_buf *buf, off_t *offset)
+{
+       u8 value;
+
+       tpm_buf_read(buf, offset, sizeof(value), &value);
+
+       return value;
+}
+EXPORT_SYMBOL_GPL(tpm_buf_read_u8);
+
+/**
+ * tpm_buf_read_u16() - Read 16-bit word from a TPM buffer
+ * @buf:       &tpm_buf instance
+ * @offset:    offset within the buffer
+ *
+ * Return: next 16-bit word
+ */
+u16 tpm_buf_read_u16(const struct tpm_buf *buf, off_t *offset)
+{
+       u16 value;
+
+       tpm_buf_read(buf, offset, sizeof(value), &value);
+
+       return be16_to_cpu(value);
+}
+EXPORT_SYMBOL_GPL(tpm_buf_read_u16);
+
+/**
+ * tpm_buf_read_u32() - Read 32-bit word from a TPM buffer
+ * @buf:       &tpm_buf instance
+ * @offset:    offset within the buffer
+ *
+ * Return: next 32-bit word
+ */
+u32 tpm_buf_read_u32(const struct tpm_buf *buf, off_t *offset)
+{
+       u32 value;
+
+       tpm_buf_read(buf, offset, sizeof(value), &value);
+
+       return be32_to_cpu(value);
+}
+EXPORT_SYMBOL_GPL(tpm_buf_read_u32);
diff --git a/include/linux/tpm.h b/include/linux/tpm.h
index 687b5173bdab..6590bd1f0a0e 100644
--- a/include/linux/tpm.h
+++ b/include/linux/tpm.h
@@ -337,6 +337,9 @@ void tpm_buf_append(struct tpm_buf *buf, const u8 
*new_data, u16 new_length);
 void tpm_buf_append_u8(struct tpm_buf *buf, const u8 value);
 void tpm_buf_append_u16(struct tpm_buf *buf, const u16 value);
 void tpm_buf_append_u32(struct tpm_buf *buf, const u32 value);
+u8 tpm_buf_read_u8(const struct tpm_buf *buf, off_t *offset);
+u16 tpm_buf_read_u16(const struct tpm_buf *buf, off_t *offset);
+u32 tpm_buf_read_u32(const struct tpm_buf *buf, off_t *offset);
 
 /*
  * Check if TPM device is in the firmware upgrade mode.
-- 
2.42.0