Re: [PATCH 2/8] tpm: Require a digest source when extending the PCR

[Ilias Apalodimas <ilias.apalodimas@linaro.org>]

On Mon, Feb 28, 2022 at 05:11:19PM -0700, Simon Glass wrote:
> This feature is used for measured boot. It is not currently supported in
> the TPM drivers, but add it to the API so that code which expects it can
> signal its request.
> 
> Signed-off-by: Simon Glass <sjg@chromium.org>
> ---
> 
>  cmd/tpm-v1.c      |  3 ++-
>  cmd/tpm_test.c    |  5 +++--
>  include/tpm_api.h |  8 +++++---
>  lib/tpm-v2.c      |  2 ++
>  lib/tpm_api.c     | 14 ++++++++++----
>  5 files changed, 22 insertions(+), 10 deletions(-)
> 
> diff --git a/cmd/tpm-v1.c b/cmd/tpm-v1.c
> index bf238a9f2e..0869b70775 100644
> --- a/cmd/tpm-v1.c
> +++ b/cmd/tpm-v1.c
> @@ -131,7 +131,8 @@ static int do_tpm_extend(struct cmd_tbl *cmdtp, int flag, int argc,
>  		return CMD_RET_FAILURE;
>  	}
>  
> -	rc = tpm_pcr_extend(dev, index, in_digest, out_digest);
> +	rc = tpm_pcr_extend(dev, index, in_digest, sizeof(in_digest),
> +			    out_digest, "test");

Where is the output value of an extended PCR needed in measured boot?
IMHO this out_digest seems pointless.  I'd be happier if we just completely
removed it and make the v2 variant look like v1 more. 

>  	if (!rc) {
>  		puts("PCR value after execution of the command:\n");
>  		print_byte_string(out_digest, sizeof(out_digest));
> diff --git a/cmd/tpm_test.c b/cmd/tpm_test.c
> index a3ccb12f53..b35eae81dc 100644
> --- a/cmd/tpm_test.c
> +++ b/cmd/tpm_test.c
> @@ -91,7 +91,8 @@ static int test_early_extend(struct udevice *dev)
>  	tpm_init(dev);
>  	TPM_CHECK(tpm_startup(dev, TPM_ST_CLEAR));
>  	TPM_CHECK(tpm_continue_self_test(dev));
> -	TPM_CHECK(tpm_pcr_extend(dev, 1, value_in, value_out));
> +	TPM_CHECK(tpm_pcr_extend(dev, 1, value_in, sizeof(value_in), value_out,
> +				 "test"));
>  	printf("done\n");
>  	return 0;
>  }
> @@ -438,7 +439,7 @@ static int test_timing(struct udevice *dev)
>  		   100);
>  	TTPM_CHECK(tpm_nv_read_value(dev, INDEX0, (uint8_t *)&x, sizeof(x)),
>  		   100);
> -	TTPM_CHECK(tpm_pcr_extend(dev, 0, in, out), 200);
> +	TTPM_CHECK(tpm_pcr_extend(dev, 0, in, sizeof(in), out, "test"), 200);
>  	TTPM_CHECK(tpm_set_global_lock(dev), 50);
>  	TTPM_CHECK(tpm_tsc_physical_presence(dev, PHYS_PRESENCE), 100);
>  	printf("done\n");
> diff --git a/include/tpm_api.h b/include/tpm_api.h
> index 11aa14eb79..3c8e48bc25 100644
> --- a/include/tpm_api.h
> +++ b/include/tpm_api.h
> @@ -81,14 +81,16 @@ u32 tpm_nv_write_value(struct udevice *dev, u32 index, const void *data,
>   *
>   * @param dev		TPM device
>   * @param index		index of the PCR
> - * @param in_digest	160-bit value representing the event to be
> + * @param in_digest	160/256-bit value representing the event to be
>   *			recorded
> - * @param out_digest	160-bit PCR value after execution of the
> + * @param size		size of digest in bytes
> + * @param out_digest	160/256-bit PCR value after execution of the
>   *			command
> + * @param name		additional info about where the digest comes from
>   * Return: return code of the operation
>   */
>  u32 tpm_pcr_extend(struct udevice *dev, u32 index, const void *in_digest,
> -		   void *out_digest);
> +		   uint size, void *out_digest, const char *name);
>  
>  /**
>   * Issue a TPM_PCRRead command.
> diff --git a/lib/tpm-v2.c b/lib/tpm-v2.c
> index 1bf627853a..6058f2e1e4 100644
> --- a/lib/tpm-v2.c
> +++ b/lib/tpm-v2.c
> @@ -157,6 +157,8 @@ u32 tpm2_pcr_extend(struct udevice *dev, u32 index, u32 algorithm,
>  	};
>  	int ret;
>  
> +	if (!digest)
> +		return -EINVAL;
>  	/*
>  	 * Fill the command structure starting from the first buffer:
>  	 *     - the digest
> diff --git a/lib/tpm_api.c b/lib/tpm_api.c
> index 4ac4612c81..a8d3731d3a 100644
> --- a/lib/tpm_api.c
> +++ b/lib/tpm_api.c
> @@ -140,15 +140,21 @@ u32 tpm_write_lock(struct udevice *dev, u32 index)
>  }
>  
>  u32 tpm_pcr_extend(struct udevice *dev, u32 index, const void *in_digest,
> -		   void *out_digest)
> +		   uint size, void *out_digest, const char *name)
>  {
> -	if (tpm_is_v1(dev))
> +	if (tpm_is_v1(dev)) {
> +		if (size != PCR_DIGEST_LENGTH || !out_digest)
> +			return -EINVAL;
>  		return tpm1_extend(dev, index, in_digest, out_digest);
> -	else if (tpm_is_v2(dev))
> +	} else if (tpm_is_v2(dev)) {
> +		if (size != TPM2_SHA256_DIGEST_SIZE)
> +			return -EINVAL;

Why are we limiting this?  This is supposed to be dictated by the PCR bank
configuration of each hardware 

>  		return tpm2_pcr_extend(dev, index, TPM2_ALG_SHA256, in_digest,
>  				       TPM2_DIGEST_LEN);
> -	else
> +		/* @name is ignored as we do not support measured boot */
> +	} else {
>  		return -ENOSYS;
> +	}
>  }
>  
>  u32 tpm_pcr_read(struct udevice *dev, u32 index, void *data, size_t count)
> -- 
> 2.35.1.574.g5d30c73bfb-goog
> 

Thanks
/Ilias