Re: [PATCH 06/10] tpm: introduce tpm_buf

["Peter Hüwe" <PeterHuewe@gmx.de>]

Am Freitag, 16. Oktober 2015, 20:40:25 schrieb Jarkko Sakkinen:
> This patch introduces struct tpm_buf that provides a string buffer for
> constructing TPM commands. This allows to construct variable sized TPM
> commands. For the buffer a page is allocated and mapped, which limits
> maximum size to PAGE_SIZE.
> 
> Variable sized TPM commands are needed in order to add algorithmic
> agility.
> 
> Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
> ---
>  drivers/char/tpm/tpm.h | 97
> ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 97
> insertions(+)
> 
> diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
> index 36ceb71..cb46f62 100644
> --- a/drivers/char/tpm/tpm.h
> +++ b/drivers/char/tpm/tpm.h
> @@ -1,5 +1,6 @@
>  /*
>   * Copyright (C) 2004 IBM Corporation
> + * Copyright (C) 2015 Intel Corporation
>   *
>   * Authors:
>   * Leendert van Doorn <leendert@watson.ibm.com>
> @@ -28,6 +29,7 @@
>  #include <linux/tpm.h>
>  #include <linux/acpi.h>
>  #include <linux/cdev.h>
> +#include <linux/highmem.h>
> 
>  enum tpm_const {
>  	TPM_MINOR = 224,	/* officially assigned */
> @@ -390,6 +392,101 @@ struct tpm_cmd_t {
>  	tpm_cmd_params	params;
>  } __packed;
> 
> +/* A string buffer type for constructing TPM commands. This is based on
> the + * ideas of string buffer code in security/keys/trusted.h but is heap
> based + * in order to keep the stack usage minimal.
> + */
> +
> +enum tpm_buf_flags {
> +	TPM_BUF_OVERFLOW	= BIT(0),
> +};
> +
> +struct tpm_buf {
> +	struct page *data_page;
> +	unsigned int flags;
> +	u8 *data;
> +};
> +
> +static inline void tpm_buf_init(struct tpm_buf *buf, u16 tag, u32 ordinal)
> +{
> +	struct tpm_input_header *head;
> +
> +	buf->data_page = alloc_page(GFP_HIGHUSER);
> +	if (!buf->data_page)
> +		return -ENOMEM;
> +
> +	buf->flags = 0;
> +	buf->data = kmap(buf->data_page);
> +
> +	head = (struct tpm_input_header *) buf->data;
> +
> +	head->tag = cpu_to_be16(tag);
> +	head->length = cpu_to_be32(sizeof(*head));
> +	head->ordinal = cpu_to_be32(ordinal);
> +
> +	return 0;
> +}
> +
> +static inline void tpm_buf_destroy(struct tpm_buf *buf)
> +{
> +	kunmap(buf->data_page);
> +	__free_page(buf->data_page);
> +}
> +
> +static inline u32 tpm_buf_length(struct tpm_buf *buf)
> +{
> +	struct tpm_input_header *head = (struct tpm_input_header *) buf->data;
> +
> +	return be32_to_cpu(head->length);
> +}
> +
> +static inline u16 tpm_buf_tag(struct tpm_buf *buf)
> +{
> +	struct tpm_input_header *head = (struct tpm_input_header *) buf->data;
> +
> +	return be16_to_cpu(head->tag);
> +}
> +
> +static inline void tpm_buf_append(struct tpm_buf *buf,
> +				  const unsigned char *new_data,
> +				  unsigned int new_len)
> +{
> +	struct tpm_input_header *head = (struct tpm_input_header *) buf->data;
> +	u32 len = tpm_buf_length(buf);


> +
> +	/* Return silently if overflow has already happened. */
> +	if (buf->flags & TPM_BUF_OVERFLOW)
> +		return;
> +
> +	if ((len + new_len) > PAGE_SIZE) {
> +		WARN(1, "tpm_buf: overflow\n");
> +		buf->flags |= TPM_BUF_OVERFLOW;
> +		return;
> +	}
Why not use WARN_ONCE?

> +
> +	memcpy(&buf->data[len], new_data, new_len);
> +	head->length = cpu_to_be32(len + new_len);
> +}
> +
> +static inline void tpm_buf_append_u8(struct tpm_buf *buf, const u8 value)
> +{
> +	tpm_buf_append(buf, &value, 1);
> +}
> +
> +static inline void tpm_buf_append_u16(struct tpm_buf *buf, const u16
> value) +{
> +	__be16 value2 = cpu_to_be16(value);
> +
> +	tpm_buf_append(buf, (u8 *) &value2, 2);
> +}
> +
> +static inline void tpm_buf_append_u32(struct tpm_buf *buf, const u32
> value) +{
> +	__be32 value2 = cpu_to_be32(value);
> +
> +	tpm_buf_append(buf, (u8 *) &value2, 4);
> +}
> +
>  extern struct class *tpm_class;
>  extern dev_t tpm_devt;
>  extern const struct file_operations tpm_fops;