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 <jar...@kernel.org> --- 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-c71398422...@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..f0b122a1c2d9 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. -- 2.42.1
