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fix loading of parent handles in TPM TSS2 keys #175

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Merged
gotthardp merged 1 commit into from
Apr 26, 2026
Merged

fix loading of parent handles in TPM TSS2 keys #175

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2 changes: 2 additions & 0 deletions Makefile.am
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Original file line number Diff line number Diff line change
Expand Up @@ -100,6 +100,8 @@ TESTS_SHELL = test/list.sh \
test/rsa_genpkey_sign.sh \
test/rsa_genpkey_sign_rawin.sh \
test/rsa_genpkey_auth_parent.sh \
test/rsa_encodeobject_check.sh \
test/rsa_encodeobject_check_parent.sh \
test/rsa_createak_auth.sh \
test/rsa_createak_sign_object.sh \
test/rsa_createak_sign_handle.sh \
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38 changes: 26 additions & 12 deletions src/tpm2-provider-pkey.c
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Expand Up @@ -53,6 +53,8 @@ int
tpm2_keydata_write(const TPM2_KEYDATA *keydata, BIO *bout, TPM2_PKEY_FORMAT format)
{
TSSPRIVKEY *tpk = NULL;
BIGNUM *bn_parent = NULL;
int res = 0;

uint8_t privbuf[sizeof(keydata->priv)];
uint8_t pubbuf[sizeof(keydata->pub)];
Expand All @@ -74,13 +76,18 @@ tpm2_keydata_write(const TPM2_KEYDATA *keydata, BIO *bout, TPM2_PKEY_FORMAT form
if (!tpk->type)
goto error;

// note the ASN1_INTEGER_set is not reliable for uin32_t on 32-bit machines
tpk->emptyAuth = ! !keydata->emptyAuth;

// note the ASN1_INTEGER_set is not reliable for uin32_t on 32-bit machines
if (!(bn_parent = BN_new()))
goto error;

if (keydata->parent != 0)
ASN1_INTEGER_set_uint64(tpk->parent, keydata->parent);
BN_set_word(bn_parent, keydata->parent);
else
ASN1_INTEGER_set_uint64(tpk->parent, TPM2_RH_OWNER);
BN_set_word(bn_parent, TPM2_RH_OWNER);

BN_to_ASN1_INTEGER(bn_parent, tpk->parent);
ASN1_STRING_set(tpk->privkey, &privbuf[0], privbuf_len);
ASN1_STRING_set(tpk->pubkey, &pubbuf[0], pubbuf_len);

Expand All @@ -95,11 +102,11 @@ tpm2_keydata_write(const TPM2_KEYDATA *keydata, BIO *bout, TPM2_PKEY_FORMAT form
goto error;
}

TSSPRIVKEY_free(tpk);
return 1;
res = 1;
error:
BN_free(bn_parent);
TSSPRIVKEY_free(tpk);
return 0;
return res;
}

/** Deserialize TPM2_KEYDATA from disk
Expand All @@ -114,9 +121,11 @@ tpm2_keydata_write(const TPM2_KEYDATA *keydata, BIO *bout, TPM2_PKEY_FORMAT form
int
tpm2_keydata_read(BIO *bin, TPM2_KEYDATA *keydata, TPM2_PKEY_FORMAT format)
{
uint64_t parent;
BIGNUM *bn_parent = NULL;
TPM2_HANDLE parent;
TSSPRIVKEY *tpk = NULL;
char type_oid[64];
int res = 0;

switch (format) {
case KEY_FORMAT_PEM:
Expand All @@ -135,9 +144,14 @@ tpm2_keydata_read(BIO *bin, TPM2_KEYDATA *keydata, TPM2_PKEY_FORMAT format)
keydata->emptyAuth = (tpk->emptyAuth != V_ASN1_UNDEF && tpk->emptyAuth);

// the ASN1_INTEGER_get on a 32-bit machine will fail for numbers of UINT32_MAX
if (!ASN1_INTEGER_get_uint64(&parent, tpk->parent))
if (!(bn_parent = ASN1_INTEGER_to_BN(tpk->parent, NULL)))
goto error;

if (BN_is_negative(bn_parent))
parent = ASN1_INTEGER_get(tpk->parent);
else
parent = BN_get_word(bn_parent);

if (parent == 0)
keydata->parent = TPM2_RH_OWNER;
else if (parent <= UINT32_MAX)

@thomkopp thomkopp Apr 27, 2026

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By changing parent from type uint64_t to TPM2_HANDLE (which according to tpm2-tss is an uint32_t see: https://github.com/tpm2-software/tpm2-tss/blob/a54a27df0732cde2c47b1d4d0e7bef489dc8a7d5/include/tss2/tss2_tpm2_types.h#L1050 and https://github.com/tpm2-software/tpm2-tss/blob/a54a27df0732cde2c47b1d4d0e7bef489dc8a7d5/include/tss2/tss2_common.h#L24) this line will always be true.

Have a look at line 153:
BN_get_word returns an BN_ULONG, which is 32-bits on 32-bit systems and 64-bits on 64-bit systems.
BN_get_word set's all bits in case of an error.

parent is of type TPM2_HANDLE which is of type uint32_t.

On a 64 bit system, we're performing an implicit conversion from uint64 to uint32. This shouldn't be a problem in case of a valid parent-handle as they're in the range 0x81000000 - 0x81FFFFFF. I think we should handle the case where BN_get_word() returns something bigger than a 32bit value on 64bits systems and on 32bit systems we should treat the return value UINT32_MAX as error.

Expand All @@ -159,11 +173,11 @@ tpm2_keydata_read(BIO *bin, TPM2_KEYDATA *keydata, TPM2_PKEY_FORMAT format)
&keydata->pub))
goto error;

res = 1;
error:
BN_free(bn_parent);
TSSPRIVKEY_free(tpk);
return 1;
error:
TSSPRIVKEY_free(tpk);
return 0;
return res;
}

static const TPM2B_PUBLIC primaryRsaTemplate = {
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27 changes: 27 additions & 0 deletions test/rsa_encodeobject_check.sh
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Original file line number Diff line number Diff line change
@@ -0,0 +1,27 @@
#!/usr/bin/env bash
# SPDX-License-Identifier: BSD-3-Clause
set -eufx

# create primary using the same ECC template that tpm2-openssl uses internally
tpm2_createprimary \
-G ecc256:aes128cfb \
-g sha256 \
-a 'fixedtpm|fixedparent|sensitivedataorigin|userwithauth|noda|restricted|decrypt' \
-c primary.ctx

# generate a private key and store its public portions to PEM
tpm2_create -C primary.ctx -u key.pub -r key.priv -f pem -o pub.pem

# encode private key to PEM
tpm2_encodeobject -C primary.ctx -u key.pub -r key.priv -o priv.pem

# print public key modulus
openssl rsa -pubin -in pub.pem -modulus -noout

# validate the private key
openssl rsa -provider tpm2 -provider base -in priv.pem -passin pass: -check -noout

# print private key modulus
openssl rsa -provider tpm2 -provider base -in priv.pem -passin pass: -modulus -noout

rm primary.ctx key.pub key.priv pub.pem priv.pem
29 changes: 29 additions & 0 deletions test/rsa_encodeobject_check_parent.sh
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Original file line number Diff line number Diff line change
@@ -0,0 +1,29 @@
#!/usr/bin/env bash
# SPDX-License-Identifier: BSD-3-Clause
set -eufx

# create primary key
tpm2_createprimary -c primary.ctx

# make the primary persistent
HANDLE=$(tpm2_evictcontrol -c primary.ctx | cut -d ' ' -f 2 | head -n 1)

# generate a private key and store its public portions to PEM
tpm2_create -C primary.ctx -u key.pub -r key.priv -f pem -o pub.pem

# encode private key to PEM using the persistent parent handle
tpm2_encodeobject -C ${HANDLE} -u key.pub -r key.priv -o priv.pem

# print public key modulus
openssl rsa -pubin -in pub.pem -modulus -noout

# validate the private key
openssl rsa -provider tpm2 -provider base -in priv.pem -passin pass: -check -noout

# print private key modulus
openssl rsa -provider tpm2 -provider base -in priv.pem -passin pass: -modulus -noout

# release the persistent primary
tpm2_evictcontrol -c ${HANDLE}

rm primary.ctx key.pub key.priv pub.pem priv.pem
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