linux-kernel - Re: [RFC PATCH 3/4] tpm: Conditionally use static buffer in TPM buffer management

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Date:   Mon, 2 Nov 2020 14:16:37 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     "Daniel P. Smith" <dpsmith@...rtussolutions.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-integrity@...r.kernel.org, ross.philipson@...cle.com,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        luto@...capital.net, trenchboot-devel@...glegroups.com
Subject: Re: [RFC PATCH 3/4] tpm: Conditionally use static buffer in TPM
 buffer management

On Sat, Oct 31, 2020 at 12:51:21PM -0400, Daniel P. Smith wrote:
> Memory management calls cannot be made in the compressed kernel
> environment to dynamically allocate TPM buffer space. For the Secure
> Launch early PCR extend code, use a static buffer instead.
> 
> Signed-off-by: Daniel P. Smith <dpsmith@...rtussolutions.com>
> Signed-off-by: Ross Philipson <ross.philipson@...cle.com>
> ---

This patch is not necessary.

Just assign tb->data to the static buffer where you use the static
buffer and use tpm_buf_reset().

tpm_buf_init() and tpm_buf_destroy() are optional.

/Jarkko

>  include/linux/tpm_buffer.h | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/include/linux/tpm_buffer.h b/include/linux/tpm_buffer.h
> index 8144a52fbc0a..c9482edf6618 100644
> --- a/include/linux/tpm_buffer.h
> +++ b/include/linux/tpm_buffer.h
> @@ -18,6 +18,10 @@
>  #ifndef __LINUX_TPM_BUFFER_H__
>  #define __LINUX_TPM_BUFFER_H__
>  
> +#ifdef COMPRESSED_KERNEL
> +static u8 _tpm_buffer[PAGE_SIZE] = {0};
> +#endif
> +
>  struct tpm_header {
>  	__be16 tag;
>  	__be32 length;
> @@ -52,7 +56,11 @@ static inline void tpm_buf_reset(struct tpm_buf *buf, u16 tag, u32 ordinal)
>  
>  static inline int tpm_buf_init(struct tpm_buf *buf, u16 tag, u32 ordinal)
>  {
> +#ifdef COMPRESSED_KERNEL
> +	buf->data = _tpm_buffer;
> +#else
>  	buf->data = (u8 *)__get_free_page(GFP_KERNEL);
> +#endif
>  	if (!buf->data)
>  		return -ENOMEM;
>  
> @@ -63,7 +71,9 @@ static inline int tpm_buf_init(struct tpm_buf *buf, u16 tag, u32 ordinal)
>  
>  static inline void tpm_buf_destroy(struct tpm_buf *buf)
>  {
> +#ifndef COMPRESSED_KERNEL
>  	free_page((unsigned long)buf->data);
> +#endif
>  }
>  
>  static inline u32 tpm_buf_length(struct tpm_buf *buf)
> @@ -92,7 +102,9 @@ static inline void tpm_buf_append(struct tpm_buf *buf,
>  		return;
>  
>  	if ((len + new_len) > PAGE_SIZE) {
> +#ifndef COMPRESSED_KERNEL
>  		WARN(1, "tpm_buf: overflow\n");
> +#endif
>  		buf->flags |= TPM_BUF_OVERFLOW;
>  		return;
>  	}
> -- 
> 2.11.0
> 

/Jarkko