On 10/23/2023 20:15, Jarkko Sakkinen wrote:
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 <jarkko@xxxxxxxxxx>
---
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;
+ }
In the overflow case wouldn't you want to pass an error code up instead
of just showing a WARN trace?
The helper functions can't tell the difference, and the net outcome is
going to be that if there is overflow you get a warning trace in the
kernel log and whatever garbage "value" happened to have going to the
caller. It's a programmer error but it's also unpredictable what
happens here.
I think it's cleaner to have callers of
tpm_buf_read_u8/tpm_buf_read_u16/tpm_buf_read_u32 to to be able to know
something wrong happened.
+
+ 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.
