[PATCH v6 7/8] tpm: Add tpm_buf_read_{u8,u16,u32}

Jarkko Sakkinen
2023-11-24T02:03:03Z

Declare reader functions for the instances of struct tpm_buf. If the read
goes out of boundary, TPM_BUF_BOUNDARY_ERROR is set, and subsequent read
will do nothing.

Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
---
v5 [2023-11-24]: Fixed off-by-one error in the boundary check.
v4 [2023-11-21]: Address James Bottomley's feedback for v2 of this
patch, i.e. offset pointer was not correctly dereferenced.
v3 [2023-11-21]: Add possibility to check for boundary error to the
as response to the feedback from Mario Limenciello:
https://lore.kernel.org/linux-integrity/3f9086f6-935f-48a7-889b-c71398422fa1@amd.com/
---
drivers/char/tpm/tpm-buf.c | 79 +++++++++++++++++++++++++++++++++++++-
include/linux/tpm.h | 5 +++
2 files changed, 83 insertions(+), 1 deletion(-)

diff --git a/drivers/char/tpm/tpm-buf.c b/drivers/char/tpm/tpm-buf.c
index 099b4a56c5d5..32619e9ab4fa 100644
--- a/drivers/char/tpm/tpm-buf.c
+++ b/drivers/char/tpm/tpm-buf.c
@@ -107,7 +107,7 @@ void tpm_buf_append(struct tpm_buf *buf, const u8 *new_data, u16 new_length)
return;

if ((buf->length + new_length) > PAGE_SIZE) {
- WARN(1, "tpm_buf: overflow\n");
+ WARN(1, "tpm_buf: write overflow\n");
buf->flags |= TPM_BUF_OVERFLOW;
return;
}
@@ -143,3 +143,80 @@ 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(struct tpm_buf *buf, off_t *offset, size_t count, void *output)
+{
+ off_t next_offset;
+
+ /* Return silently if overflow has already happened. */
+ if (buf->flags & TPM_BUF_BOUNDARY_ERROR)
+ return;
+
+ next_offset = *offset + count;
+ if (next_offset > buf->length) {
+ WARN(1, "tpm_buf: read out of boundary\n");
+ buf->flags |= TPM_BUF_BOUNDARY_ERROR;
+ return;
+ }
+
+ memcpy(output, &buf->data[*offset], count);
+ *offset = next_offset;
+}
+
+/**
+ * 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(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(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(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 715db4a91c1f..e8172f81c562 100644
--- a/include/linux/tpm.h
+++ b/include/linux/tpm.h
@@ -302,6 +302,8 @@ enum tpm_buf_flags {
TPM_BUF_OVERFLOW = BIT(0),
/* TPM2B format: */
TPM_BUF_TPM2B = BIT(1),
+ /* read out of boundary: */
+ TPM_BUF_BOUNDARY_ERROR = BIT(2),
};

/*
@@ -338,6 +340,9 @@ 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(struct tpm_buf *buf, off_t *offset);
+u16 tpm_buf_read_u16(struct tpm_buf *buf, off_t *offset);
+u32 tpm_buf_read_u32(struct tpm_buf *buf, off_t *offset);

/*
* Check if TPM device is in the firmware upgrade mode.
--
2.43.0