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2025-02-09crypto: ecdsa - Harden against integer overflows in DIV_ROUND_UP()Lukas Wunner
Herbert notes that DIV_ROUND_UP() may overflow unnecessarily if an ecdsa implementation's ->key_size() callback returns an unusually large value. Herbert instead suggests (for a division by 8): X / 8 + !!(X & 7) Based on this formula, introduce a generic DIV_ROUND_UP_POW2() macro and use it in lieu of DIV_ROUND_UP() for ->key_size() return values. Additionally, use the macro in ecc_digits_from_bytes(), whose "nbytes" parameter is a ->key_size() return value in some instances, or a user-specified ASN.1 length in the case of ecdsa_get_signature_rs(). Link: https://lore.kernel.org/r/Z3iElsILmoSu6FuC@gondor.apana.org.au/ Signed-off-by: Lukas Wunner <lukas@wunner.de> Signed-off-by: Lukas Wunner <lukas@wunner.de> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2024-10-05crypto: ecdsa - Support P1363 signature decodingLukas Wunner
Alternatively to the X9.62 encoding of ecdsa signatures, which uses ASN.1 and is already supported by the kernel, there's another common encoding called P1363. It stores r and s as the concatenation of two big endian, unsigned integers. The name originates from IEEE P1363. Add a P1363 template in support of the forthcoming SPDM library (Security Protocol and Data Model) for PCI device authentication. P1363 is prescribed by SPDM 1.2.1 margin no 44: "For ECDSA signatures, excluding SM2, in SPDM, the signature shall be the concatenation of r and s. The size of r shall be the size of the selected curve. Likewise, the size of s shall be the size of the selected curve. See BaseAsymAlgo in NEGOTIATE_ALGORITHMS for the size of r and s. The byte order for r and s shall be in big endian order. When placing ECDSA signatures into an SPDM signature field, r shall come first followed by s." Link: https://www.dmtf.org/sites/default/files/standards/documents/DSP0274_1.2.1.pdf Signed-off-by: Lukas Wunner <lukas@wunner.de> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com> Reviewed-by: Stefan Berger <stefanb@linux.ibm.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>