linux-kernel - Re: [PATCH v3 01/14] mpi: Introduce mpi_key

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Message-Id: <D44C94RCUEH1.1DTWZRGG5J5PJ@kernel.org>
Date: Thu, 12 Sep 2024 16:26:32 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Roberto Sassu" <roberto.sassu@...weicloud.com>, <dhowells@...hat.com>,
 <dwmw2@...radead.org>, <herbert@...dor.apana.org.au>, <davem@...emloft.net>
Cc: <linux-kernel@...r.kernel.org>, <keyrings@...r.kernel.org>,
 <linux-crypto@...r.kernel.org>, <zohar@...ux.ibm.com>,
 <linux-integrity@...r.kernel.org>, <torvalds@...ux-foundation.org>,
 "Roberto Sassu" <roberto.sassu@...wei.com>
Subject: Re: [PATCH v3 01/14] mpi: Introduce mpi_key_length()

On Wed Sep 11, 2024 at 3:28 PM EEST, Roberto Sassu wrote:
> From: Roberto Sassu <roberto.sassu@...wei.com>
>
> Introduce the new function to get the number of bits and bytes from an MPI.
>
> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
> Signed-off-by: David Howells <dhowells@...hat.com>
> ---
>  include/linux/mpi.h       |  2 ++
>  lib/crypto/mpi/mpicoder.c | 33 ++++++++++++++++++++++++++-------
>  2 files changed, 28 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/mpi.h b/include/linux/mpi.h
> index eb0d1c1db208..a7dd4c9d8120 100644
> --- a/include/linux/mpi.h
> +++ b/include/linux/mpi.h
> @@ -90,6 +90,8 @@ enum gcry_mpi_format {
>  };
>  
>  MPI mpi_read_raw_data(const void *xbuffer, size_t nbytes);
> +int mpi_key_length(const void *xbuffer, unsigned int ret_nread,
> +		   unsigned int *nbits_arg, unsigned int *nbytes_arg);

"_arg" - what is the point of this?

>  MPI mpi_read_from_buffer(const void *buffer, unsigned *ret_nread);
>  int mpi_fromstr(MPI val, const char *str);
>  MPI mpi_scanval(const char *string);
> diff --git a/lib/crypto/mpi/mpicoder.c b/lib/crypto/mpi/mpicoder.c
> index 3cb6bd148fa9..92447a1c8bf9 100644
> --- a/lib/crypto/mpi/mpicoder.c
> +++ b/lib/crypto/mpi/mpicoder.c
> @@ -79,22 +79,41 @@ MPI mpi_read_raw_data(const void *xbuffer, size_t nbytes)
>  }
>  EXPORT_SYMBOL_GPL(mpi_read_raw_data);
>  
> -MPI mpi_read_from_buffer(const void *xbuffer, unsigned *ret_nread)
> +int mpi_key_length(const void *xbuffer, unsigned int ret_nread,
> +		   unsigned int *nbits_arg, unsigned int *nbytes_arg)
>  {
>  	const uint8_t *buffer = xbuffer;
> -	unsigned int nbits, nbytes;
> -	MPI val;
> +	unsigned int nbits;
>  
> -	if (*ret_nread < 2)
> -		return ERR_PTR(-EINVAL);
> +	if (ret_nread < 2)
> +		return -EINVAL;
>  	nbits = buffer[0] << 8 | buffer[1];
>  
>  	if (nbits > MAX_EXTERN_MPI_BITS) {
>  		pr_info("MPI: mpi too large (%u bits)\n", nbits);
> -		return ERR_PTR(-EINVAL);
> +		return -EINVAL;
>  	}
>  
> -	nbytes = DIV_ROUND_UP(nbits, 8);
> +	if (nbits_arg)
> +		*nbits_arg = nbits;
> +	if (nbytes_arg)
> +		*nbytes_arg = DIV_ROUND_UP(nbits, 8);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(mpi_key_length);
> +
> +MPI mpi_read_from_buffer(const void *xbuffer, unsigned int *ret_nread)
> +{
> +	const uint8_t *buffer = xbuffer;
> +	unsigned int nbytes;
> +	MPI val;
> +	int ret;
> +
> +	ret = mpi_key_length(xbuffer, *ret_nread, NULL, &nbytes);
> +	if (ret < 0)
> +		return ERR_PTR(ret);
> +
>  	if (nbytes + 2 > *ret_nread) {
>  		pr_info("MPI: mpi larger than buffer nbytes=%u ret_nread=%u\n",
>  				nbytes, *ret_nread);

BR, Jarkko