Re: [PATCH ima-evm-utils] ima-evm-utils: ima_sign supports SM2 and SM3 algorithm combination

[Vitaly Chikunov <vt@altlinux.org>]

Tianjia,

On Sun, Jan 31, 2021 at 08:56:23PM +0300, Vitaly Chikunov wrote:
> On Sun, Jan 31, 2021 at 08:48:46PM +0300, Vitaly Chikunov wrote:
> > On Sun, Jan 31, 2021 at 11:27:21AM +0800, Tianjia Zhang wrote:
> > > The combination of SM2 and SM3 algorithms has been implemented in the
> > > kernel. At present, the ima-evm-utils signature tool does not support
> > > this combination of algorithms. This is because SM2 sign require a
> > > USERID, which requires the use of a higher-level sign functions of
> > > OpenSSL. this patch use the EVP_DigestSign series of functions to
> > > sign to support various signature algorithm combinations.
> > > 
> > > Signed-off-by: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
> > > ---
> > >  src/libimaevm.c | 37 +++++++++++++++++++++++++++++++------
> > >  1 file changed, 31 insertions(+), 6 deletions(-)
> > > 
> > > diff --git a/src/libimaevm.c b/src/libimaevm.c
> > > index fa6c278..89b9b88 100644
> > > --- a/src/libimaevm.c
> > > +++ b/src/libimaevm.c
> > > @@ -891,6 +891,7 @@ static int sign_hash_v2(const char *algo, const unsigned char *hash,
> > >  	EVP_PKEY *pkey;
> > >  	char name[20];
> > >  	EVP_PKEY_CTX *ctx = NULL;
> > > +	EVP_MD_CTX *mctx = NULL;
> > >  	const EVP_MD *md;
> > >  	size_t sigsize;
> > >  	const char *st;
> > > @@ -932,24 +933,47 @@ static int sign_hash_v2(const char *algo, const unsigned char *hash,
> > >  		return -1;
> > >  	}
> > >  
> > > +#if OPENSSL_VERSION_NUMBER < 0x30000000
> > 
> > Perhaps, this check is not needed at all if it isn't enabled for new
> > openssl?
> > 
> > 
> > > +	/*
> > > +	 * SM2 and SM3 should go together. If SM3 hash algorithm and EC private
> > > +	 * key are used at the same time, check whether it is SM2 private key.
> > > +	 */
> > > +	if (hdr->hash_algo == PKEY_HASH_SM3_256 && EVP_PKEY_id(pkey) == EVP_PKEY_EC) {
> > > +		EC_KEY *ec = EVP_PKEY_get0_EC_KEY(pkey);
> > > +		int curve = EC_GROUP_get_curve_name(EC_KEY_get0_group(ec));
> > > +		if (curve == NID_sm2)

Also, this patch does not compile on openssl 1.1.0 because 
NID_sm2 and EVP_PKEY_SM2 are not defined.

> > > +			EVP_PKEY_set_alias_type(pkey, EVP_PKEY_SM2);
> > > +	}
> > > +#endif
> > > +
> > >  	calc_keyid_v2(&keyid, name, pkey);
> > >  	hdr->keyid = keyid;
> > >  
> > >  	st = "EVP_PKEY_CTX_new";
> > >  	if (!(ctx = EVP_PKEY_CTX_new(pkey, NULL)))
> > >  		goto err;
> > > -	st = "EVP_PKEY_sign_init";
> > > -	if (!EVP_PKEY_sign_init(ctx))
> > > +	st = "EVP_MD_CTX_new";
> > > +	if (!(mctx = EVP_MD_CTX_new()))
> > >  		goto err;
> > > +	if (EVP_PKEY_id(pkey) == EVP_PKEY_SM2) {
> > > +		st = "EVP_PKEY_CTX_set1_id";
> > > +		/* Set SM2 default userid */
> > > +		if (!EVP_PKEY_CTX_set1_id(ctx, "1234567812345678", 16))
> > 
> > You cannot call EVP_PKEY_CTX_set1_id for EVP_PKEY_sign's ctx?
> > I don't really get the API change. Can you explain more this
> > requirement?
> 
> EVP_PKEY_sign should be able to sign with any algo, unless there is
> openssl bug. Is there bug preventing SM2 signing with EVP_PKEY_sign?
> 
> > > +			goto err;
> > > +	}
> > > +	EVP_MD_CTX_set_pkey_ctx(mctx, ctx);
> > >  	st = "EVP_get_digestbyname";
> > >  	if (!(md = EVP_get_digestbyname(imaevm_params.hash_algo)))
> > >  		goto err;
> > > -	st = "EVP_PKEY_CTX_set_signature_md";
> > > -	if (!EVP_PKEY_CTX_set_signature_md(ctx, md))
> > > +	st = "EVP_DigestSignInit";
> > > +	if (!EVP_DigestSignInit(mctx, NULL, md, NULL, pkey))
> > > +		goto err;
> > > +	st = "EVP_DigestSignUpdate";
> > > +	if (!EVP_DigestSignUpdate(mctx, hash, size))
> > >  		goto err;
> > > -	st = "EVP_PKEY_sign";
> > > +	st = "EVP_DigestSignFinal";
> > >  	sigsize = MAX_SIGNATURE_SIZE - sizeof(struct signature_v2_hdr) - 1;
> > > -	if (!EVP_PKEY_sign(ctx, hdr->sig, &sigsize, hash, size))

Also, this conversion to EVP_DigestSign is incorrect, because
EVP_PKEY_sign does not hash the data (and expected to work over a ready
digest, see man EVP_PKEY_sign). While EVP_DigestSignFinal does hash the
data.

You should really try to run `make check` before sending patches.

Thanks,

> > > +	if (!EVP_DigestSignFinal(mctx, hdr->sig, &sigsize))
> > >  		goto err;
> > >  	len = (int)sigsize;
> > >  
> > > @@ -964,6 +988,7 @@ err:
> > >  			ERR_reason_error_string(ERR_peek_error()), st);
> > >  		output_openssl_errors();
> > >  	}
> > > +	EVP_MD_CTX_free(mctx);
> > >  	EVP_PKEY_CTX_free(ctx);
> > >  	EVP_PKEY_free(pkey);
> > >  	return len;
> > > -- 
> > > 2.19.1.3.ge56e4f7