Re: [PATCH 03/12] tpm: add buffer handling for TPM2B types

[Jarkko Sakkinen <jarkko@kernel.org>]

On Thu, Feb 16, 2023 at 03:14:01PM -0500, James Bottomley wrote:
> Most complex TPM commands require appending TPM2B buffers to the
> command body.  Since TPM2B types are essentially variable size arrays,
> it makes it impossible to represent these complex command arguments as
> structures and we simply have to build them up using append primitives
> like these.
> 
> Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
> ---
>  drivers/char/tpm/tpm-buf.c | 71 +++++++++++++++++++++++++++++++++++---
>  include/linux/tpm.h        |  3 ++
>  2 files changed, 69 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm-buf.c b/drivers/char/tpm/tpm-buf.c
> index ca59b92e0f95..292c6f14f72c 100644
> --- a/drivers/char/tpm/tpm-buf.c
> +++ b/drivers/char/tpm/tpm-buf.c
> @@ -7,17 +7,16 @@
>  #include <linux/module.h>
>  #include <linux/tpm.h>
>  
> -int tpm_buf_init(struct tpm_buf *buf, u16 tag, u32 ordinal)
> +static int __tpm_buf_init(struct tpm_buf *buf)
>  {
>  	buf->data = (u8 *)__get_free_page(GFP_KERNEL);
>  	if (!buf->data)
>  		return -ENOMEM;
>  
>  	buf->flags = 0;
> -	tpm_buf_reset(buf, tag, ordinal);
> +
>  	return 0;
>  }
> -EXPORT_SYMBOL_GPL(tpm_buf_init);
>  
>  void tpm_buf_reset(struct tpm_buf *buf, u16 tag, u32 ordinal)
>  {
> @@ -29,17 +28,60 @@ void tpm_buf_reset(struct tpm_buf *buf, u16 tag, u32 ordinal)
>  }
>  EXPORT_SYMBOL_GPL(tpm_buf_reset);
>  
> +int tpm_buf_init(struct tpm_buf *buf, u16 tag, u32 ordinal)
> +{
> +	int rc;
> +
> +	rc = __tpm_buf_init(buf);
> +	if (rc)
> +		return rc;
> +
> +	tpm_buf_reset(buf, tag, ordinal);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(tpm_buf_init);
> +
> +int tpm_buf_init_2b(struct tpm_buf *buf)

kdoc

> +{
> +	struct tpm_header *head;
> +	int rc;
> +
> +	rc = __tpm_buf_init(buf);
> +	if (rc)
> +		return rc;
> +
> +	head = (struct tpm_header *) buf->data;
> +
> +	head->length = cpu_to_be32(sizeof(*head));
> +
> +	buf->flags = TPM_BUF_2B;

Please make tpm_buf_init() and tpm_buf_reset() to work for both cases.

This explodes the whole thing into an unmaintainable mess. It is better
to have a type as a parameter for tpm_buf_init() and have only single
flow instead of open coded and patched variation.

I'd simply just put it as:

struct tpm_buf *tpm_buf_init(u16 tag, u32 ordinal, bool tpm2b)

> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(tpm_buf_init_2b);
> +
>  void tpm_buf_destroy(struct tpm_buf *buf)
>  {
>  	free_page((unsigned long)buf->data);
>  }
>  EXPORT_SYMBOL_GPL(tpm_buf_destroy);
>  
> +static void *tpm_buf_data(struct tpm_buf *buf)
> +{
> +	if (buf->flags & TPM_BUF_2B)
> +		return buf->data + TPM_HEADER_SIZE;
> +	return buf->data;
> +}
> +
>  u32 tpm_buf_length(struct tpm_buf *buf)
>  {
>  	struct tpm_header *head = (struct tpm_header *)buf->data;
> +	u32 len;
>  
> -	return be32_to_cpu(head->length);
> +	len = be32_to_cpu(head->length);
> +	if (buf->flags & TPM_BUF_2B)
> +		len -= sizeof(*head);
> +	return len;
>  }
>  EXPORT_SYMBOL_GPL(tpm_buf_length);
>  
> @@ -55,7 +97,7 @@ void tpm_buf_append(struct tpm_buf *buf,
>  		    unsigned int new_len)
>  {
>  	struct tpm_header *head = (struct tpm_header *) buf->data;
> -	u32 len = tpm_buf_length(buf);
> +	u32 len = be32_to_cpu(head->length);
>  
>  	/* Return silently if overflow has already happened. */
>  	if (buf->flags & TPM_BUF_OVERFLOW)
> @@ -93,3 +135,22 @@ 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);
> +
> +static void tpm_buf_reset_int(struct tpm_buf *buf)
> +{
> +	struct tpm_header *head;
> +
> +	head = (struct tpm_header *)buf->data;
> +	head->length = cpu_to_be32(sizeof(*head));
> +}
> +
> +void tpm_buf_append_2b(struct tpm_buf *buf, struct tpm_buf *tpm2b)
> +{
> +	u16 len = tpm_buf_length(tpm2b);
> +
> +	tpm_buf_append_u16(buf, len);
> +	tpm_buf_append(buf, tpm_buf_data(tpm2b), len);
> +	/* clear the buf for reuse */
> +	tpm_buf_reset_int(tpm2b);
> +}
> +EXPORT_SYMBOL_GPL(tpm_buf_append_2b);
> diff --git a/include/linux/tpm.h b/include/linux/tpm.h
> index 150b39b6190e..f2d4dab6d832 100644
> --- a/include/linux/tpm.h
> +++ b/include/linux/tpm.h
> @@ -300,6 +300,7 @@ struct tpm_header {
>  
>  enum tpm_buf_flags {
>  	TPM_BUF_OVERFLOW	= BIT(0),
> +	TPM_BUF_2B		= BIT(1),
>  };


This is IMHO unnecessary complex.

I think we could just have two bools:

        bool overflow;
        bool tpm2b;

>  
>  struct tpm_buf {
> @@ -324,6 +325,7 @@ struct tpm2_hash {
>  
>  
>  int tpm_buf_init(struct tpm_buf *buf, u16 tag, u32 ordinal);
> +int tpm_buf_init_2b(struct tpm_buf *buf);
>  void tpm_buf_reset(struct tpm_buf *buf, u16 tag, u32 ordinal);
>  void tpm_buf_destroy(struct tpm_buf *buf);
>  u32 tpm_buf_length(struct tpm_buf *buf);
> @@ -332,6 +334,7 @@ void tpm_buf_append(struct tpm_buf *buf, const unsigned char *new_data,
>  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);
> +void tpm_buf_append_2b(struct tpm_buf *buf, struct tpm_buf *tpm2b);
>  
>  /*
>   * Check if TPM device is in the firmware upgrade mode.
> -- 
> 2.35.3
> 

BR, Jarkko