On Tue Apr 4, 2023 at 12:39 AM EEST, James Bottomley wrote:
> Extracting values from returned TPM buffers can be hard. Add cursor
> based (moving poiner) functions that make it easier to extract TPM
> returned values from a buffer.
>
> Signed-off-by: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
>
> ---
> v4: add kernel doc and reword commit
> ---
> drivers/char/tpm/tpm-buf.c | 48 ++++++++++++++++++++++++++++++++++++++
> include/linux/tpm.h | 3 +++
> 2 files changed, 51 insertions(+)
>
> diff --git a/drivers/char/tpm/tpm-buf.c b/drivers/char/tpm/tpm-buf.c
> index b7e42fb6266c..da0f6e725c3f 100644
> --- a/drivers/char/tpm/tpm-buf.c
> +++ b/drivers/char/tpm/tpm-buf.c
> @@ -6,6 +6,8 @@
> #include <linux/module.h>
> #include <linux/tpm.h>
>
> +#include <asm/unaligned.h>
> +
> static int __tpm_buf_init(struct tpm_buf *buf)
> {
> buf->data = (u8 *)__get_free_page(GFP_KERNEL);
> @@ -229,3 +231,49 @@ void tpm_buf_append_2b(struct tpm_buf *buf, struct tpm_buf *tpm2b)
> tpm_buf_reset_int(tpm2b);
> }
> EXPORT_SYMBOL_GPL(tpm_buf_append_2b);
> +
> +/* functions for unmarshalling data and moving the cursor */
> +
> +/**
> + * tpm_get_inc_u8 - read a u8 and move pointer beyond it
> + * @ptr: pointer to pointer
> + *
> + * @return: value read
> + */
> +u8 tpm_get_inc_u8(const u8 **ptr)
> +{
> + return *((*ptr)++);
> +}
> +EXPORT_SYMBOL_GPL(tpm_get_inc_u8);
No overflow check, and these should be static inlines.
Please consider this:
/**
* tpm_buf_read_u8() - Read a byte from a TPM buffer
* @buf: &tpm_buf instance
* @offset: offset within the consumed part of the buffer
*/
static inline int tpm_buf_read_u8(const struct tpm_buf *buf, offs_t *offset)
{
if (*offset++ >= buf->length)
return -EINVAL;
return buf->data[*offset - 1];
}
Depends on:
https://lore.kernel.org/linux-integrity/20230821033630.1039527-1-jarkko@xxxxxxxxxx/
No motivation for weird cursor concept, when the reality is just
a read from a buffer.
BR, Jarkko
