Trusted Key policy for TPM 2.0
Subsystems (6)
James Bottomley
maintainerv12 cover Trusted Key policy for TPM 2.0
Updated commit message
Original cover letter:
This is a lockstep patch with the prior trusted key rework patch (so requires it as a percursor). Now the key format is ASN.1, the policy statements needed to unseal the key can be coded into the key file itself meaning the kernel can now construct and use the policy session necessary rather than the user having to do it. This makes using TPM 2.0 keys with policy much easier.
The current implementation only has a limited subset of the full TPM 2.0 policy commands, but it is enough to implement keys locked to PCR values and expiring keys. The main missing feature is support for the TPM2_PolicyOR statement, which means all current policy has to be AND chains (key doesn't unlock unless every policy statement succeeds).
James
---
*** BLURB HERE ***
James Bottomley (3):
security: keys: trusted: add PCR policy to TPM2 keys
security: keys: trusted: add ability to specify arbitrary policy
security: keys: trusted: implement counter/timer policy
.../security/keys/trusted-encrypted.rst | 83 +++- include/keys/trusted-type.h | 5 +- include/linux/tpm.h | 6 + security/keys/Kconfig | 2 + security/keys/trusted-keys/Makefile | 2 +- security/keys/trusted-keys/tpm2-policy.c | 465 ++++++++++++++++++ security/keys/trusted-keys/tpm2-policy.h | 31 ++ security/keys/trusted-keys/tpm2key.asn1 | 13 + security/keys/trusted-keys/trusted_tpm1.c | 23 +- security/keys/trusted-keys/trusted_tpm2.c | 120 ++++- 10 files changed, 735 insertions(+), 15 deletions(-) create mode 100644 security/keys/trusted-keys/tpm2-policy.c create mode 100644 security/keys/trusted-keys/tpm2-policy.h
Signature · 1 line
2.26.2
James Bottomley
maintainerPATCH v12 1/3 security: keys: trusted: add PCR policy to TPM2 keys
This commit adds the ability to specify a PCR lock policy to TPM2 keys. There is a complexity in that the creator of the key must chose either to use a PCR lock policy or to use authentication. At the current time they can't use both due to a complexity with the way authentication works when policy registers are in use. The way to construct a pcrinfo statement for a key is simply to use the TPMS_PCR_SELECT structure to specify the PCRs and follow this by a hash of all their values in order of ascending PCR number.
For simplicity, we require the hash of the PCRs to use the same hash algorithm as the one passed in. Thus to construct a policy around the value of the resettable PCR 16 using the sha1 bank, first reset the PCR to zero giving a hash of all zeros as:
6768033e216468247bd031a0a2d9876d79818f8f
Then the TPMS_PCR_SELECT value for PCR 16 is
03000001
So create a new 32 byte key with a policy policy locking the key to this value of PCR 16 with a parent key of 81000001 would be:
keyctl add trusted kmk "new 32 keyhandle=0x81000001 hash=sha1 pcrinfo0000016768033e216468247bd031a0a2d9876d79818f8f" @u
---
v2: fix for new ASN.1 API eliminating hack in place and check lengths
v8: recover patch and fix offsets for hash and size
v9: fix cut and paste error in commit log
v10: update for kfree_sensitive()
v11: add policy to ASN.1 key format description
v12: tidy up commit message and document ASN.1 parser handlers
--- .../security/keys/trusted-encrypted.rst | 36 +- include/keys/trusted-type.h | 5 +- include/linux/tpm.h | 5 + security/keys/Kconfig | 2 + security/keys/trusted-keys/Makefile | 2 +- security/keys/trusted-keys/tpm2-policy.c | 374 ++++++++++++++++++ security/keys/trusted-keys/tpm2-policy.h | 30 ++ security/keys/trusted-keys/tpm2key.asn1 | 13 + security/keys/trusted-keys/trusted_tpm1.c | 8 +- security/keys/trusted-keys/trusted_tpm2.c | 86 +++- 10 files changed, 547 insertions(+), 14 deletions(-) create mode 100644 security/keys/trusted-keys/tpm2-policy.c create mode 100644 security/keys/trusted-keys/tpm2-policy.h
Documentation/security/keys/trusted-encrypted.rst +35 -1
@@ -60,7 +60,10 @@ Usage:: (40 ascii zeros) blobauth= ascii hex auth for sealed data default 0x00... (40 ascii zeros) - pcrinfo= ascii hex of PCR_INFO or PCR_INFO_LONG (no default) + pcrinfo= ascii hex of PCR_INFO or PCR_INFO_LONG (no + default) on TPM 1.2 and a TPMS_PCR_SELECTION + coupled with a hash of all the selected PCRs on + TPM 2.0 using the selected hash. pcrlock= pcr number to be extended to "lock" blob migratable= 0|1 indicating permission to reseal to new PCR values, default 1 (resealing allowed)
@@ -151,6 +154,20 @@ Load a trusted key from the saved blob:: f1f8fff03ad0acb083725535636addb08d73dedb9832da198081e5deae84bfaf0409c22b e4a8aea2b607ec96931e6f4d4fe563ba +Create a trusted key on TPM 2.0 using an all zero value of PCR16 and +using the NV storage root 81000001 as the parent:: + + $ keyctl add trusted kmk "new 32 keyhandle=0x81000001 hash=sha1 pcrinfo0000016768033e216468247bd031a0a2d9876d79818f8f" @u + +Note the TPMS_PCR_SELECT value for PCR 16 is 03000001 because all +current TPMs have 24 PCRs, so the initial 03 says there are three +following bytes of selection and then because the bytes are big +endian, 16 is bit zero of byte 2. the hash is the sha1 sum of all +zeros (the value of PCR 16):: + + $ dd if=/dev/zero bs=1 count 2>/dev/null|sha1sum + 6768033e216468247bd031a0a2d9876d79818f8f + Reseal a trusted key under new pcr values:: $ keyctl update 268728824 "update pcrinfo=`cat pcr.blob`"
@@ -221,11 +238,17 @@ policy:: TPMKey ::= SEQUENCE { type OBJECT IDENTIFIER emptyAuth [0] EXPLICIT BOOLEAN OPTIONAL + policy [1] EXPLICIT SEQUENCE OF TPMPolicy OPTIONAL parent INTEGER pubkey OCTET STRING privkey OCTET STRING } + TPMPolicy ::= SEQUENCE { + CommandCode [0] EXPLICIT INTEGER + CommandPolicy [1] EXPLICIT OCTET STRING + } + type is what distinguishes the key even in binary form since the OID is provided by the TCG to be unique and thus forms a recognizable binary pattern at offset 3 in the key. The OIDs currently made
@@ -251,6 +274,17 @@ is false or not present, the key requires an explicit authorization phrase. This is used by most user space consumers to decide whether to prompt for a password. +policy represents a sequence of one or more policy statements that +must be executed successfully into a session policy register. If +policy isn't present then no policy is required to unlock the key, but +if it is, commandCode is the TPM 2.0 command code of the policy +instruction that must be executed and CommandPolicy represents the +binary parameter area of the policy command. + +Note that the current sequential execution requirement means that only +AND based policy can be constructed at the moment, so TPM2_PolicyOR is +not currently supported. + parent represents the parent key handle, either in the 0x81 MSO space, like 0x81000001 for the RSA primary storage key. Userspace programmes also support specifying the primary handle in the 0x40 MSO space. If
include/keys/trusted-type.h +4 -1
@@ -14,9 +14,11 @@#define MIN_KEY_SIZE 32#define MAX_KEY_SIZE 128#define MAX_BLOB_SIZE 512 -#define MAX_PCRINFO_SIZE 64 +#define MAX_PCRINFO_SIZE 128#define MAX_DIGEST_SIZE 64 +#define TPM2_MAX_POLICIES 16 +struct trusted_key_payload {struct rcu_head rcu;unsigned int key_len;
@@ -25,6 +27,7 @@ struct trusted_key_payload {unsigned char old_format;unsigned char key[MAX_KEY_SIZE +1 ];unsigned char blob[MAX_BLOB_SIZE ]; +struct tpm2_policies *policies; };struct trusted_key_options {
include/linux/tpm.h +5 -0
@@ -230,10 +230,14 @@ enum tpm2_command_codes {TPM2_CC_CONTEXT_LOAD =0x0161 ,TPM2_CC_CONTEXT_SAVE =0x0162 ,TPM2_CC_FLUSH_CONTEXT =0x0165 , +TPM2_CC_POLICY_AUTHVALUE =0x016B , +TPM2_CC_POLICY_COUNTER_TIMER =0x016D , +TPM2_CC_START_AUTH_SESS =0x0176 ,TPM2_CC_VERIFY_SIGNATURE =0x0177 ,TPM2_CC_GET_CAPABILITY =0x017A ,TPM2_CC_GET_RANDOM =0x017B ,TPM2_CC_PCR_READ =0x017E , +TPM2_CC_POLICY_PCR =0x017F ,TPM2_CC_PCR_EXTEND =0x0182 ,TPM2_CC_EVENT_SEQUENCE_COMPLETE =0x0185 , TPM2_CC_HASH_SEQUENCE_START = 0x0186,
@@ -242,6 +246,7 @@ enum tpm2_command_codes { };enum tpm2_permanent_handles { +TPM2_RH_NULL =0x40000007 ,TPM2_RS_PW =0x40000009 , };
security/keys/Kconfig +2 -0
@@ -74,6 +74,8 @@ config TRUSTED_KEYS select CRYPTO select CRYPTO_HMAC select CRYPTO_SHA1 + select CRYPTO_SHA256 + select CRYPTO_SHA512 select CRYPTO_HASH_INFO select ASN1_ENCODER help
security/keys/trusted-keys/Makefile +1 -1
@@ -5,4 +5,4 @@ obj-$(CONFIG_TRUSTED_KEYS) += trusted.o trusted-y += trusted_tpm1.o -trusted-y += trusted_tpm2.o tpm2key.asn1.o +trusted-y += trusted_tpm2.o tpm2key.asn1.o tpm2-policy.o
security/keys/trusted-keys/tpm2-policy.c new file +374 -0
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security/keys/trusted-keys/tpm2-policy.h new file +30 -0
@@ -0,0 +1,30 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ + +struct tpm2_key_context { +u32 parent; +const u8 *pub; +u32 pub_len; +const u8 *priv; +u32 priv_len; +const u8 *policies[TPM2_MAX_POLICIES ]; +u32 policy_code[TPM2_MAX_POLICIES ]; +u16 policy_len[TPM2_MAX_POLICIES ]; +u8 policy_count; +}; + +struct tpm2_policies { +u32 code[TPM2_MAX_POLICIES ]; +u8 *policies[TPM2_MAX_POLICIES ]; +u16 len[TPM2_MAX_POLICIES ]; +u8 count; +u16 hash; +u16 hash_size; +}; + +int tpm2_key_policy_process (struct tpm2_key_context *ctx, +struct trusted_key_payload *payload); +int tpm2_generate_policy_digest (struct tpm2_policies *pols,u32 hash, +u8 *policydigest,u32 *plen); +int tpm2_encode_policy (struct tpm2_policies *pols,u8 **data,u32 *len); +int tpm2_get_policy_session (struct tpm_chip *chip,struct tpm2_policies *pols, +u32 *handle);
security/keys/trusted-keys/tpm2key.asn1 +13 -0
@@ -1,11 +1,24 @@ --- --- ASN.1 for for TPM 2.0 keys --- +--- Note: This isn't quite the definition in the standard +--- However, the Linux asn.1 parser doesn't understand +--- [2] EXPLICIT SEQUENCE OF OPTIONAL +--- So there's an extra intermediate TPMPolicySequence +--- definition to work around this TPMKey ::= SEQUENCE { type OBJECT IDENTIFIER ({tpm2_key_type}), emptyAuth [0] EXPLICIT BOOLEAN OPTIONAL, + policy [1] EXPLICIT TPMPolicySequence OPTIONAL, parent INTEGER ({tpm2_key_parent}), pubkey OCTET STRING ({tpm2_key_pub}), privkey OCTET STRING ({tpm2_key_priv}) } + +TPMPolicySequence ::= SEQUENCE OF TPMPolicy + +TPMPolicy ::= SEQUENCE { + commandCode [0] EXPLICIT INTEGER ({tpm2_key_code}), + commandPolicy [1] EXPLICIT OCTET STRING ({tpm2_key_policy}) + }
security/keys/trusted-keys/trusted_tpm1.c +7 -1
@@ -1065,6 +1065,8 @@ static void trusted_rcu_free(struct rcu_head *rcu)struct trusted_key_payload *p; p = container_of(rcu, struct trusted_key_payload, rcu); + +kfree_sensitive (p->policies);kfree_sensitive (p); }
@@ -1174,7 +1176,11 @@ static long trusted_read(const struct key *key, char *buffer,*/ static void trusted_destroy (struct key *key) { -kfree_sensitive (key->payload.data[0 ]); +struct trusted_key_payload *p; + + p = key->payload.data[0 ]; +kfree_sensitive (p->policies); +kfree_sensitive (p); }struct key_type key_type_trusted = {
security/keys/trusted-keys/trusted_tpm2.c +76 -10
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Signature · 1 line
2.26.2
James Bottomley
maintainerPATCH v12 2/3 security: keys: trusted: add ability to specify arbitrary policy
In reply to James BottomleyThis patch adds a policy= argument to key creation. The policy is the standard tss policymaker format and each separate policy line must have a newline after it.
Thus to construct a policy requiring authorized value and pcr 16 locking using a sha256 hash, the policy (policy.txt) file would be two lines:
0000017F00000001000B03000001303095B49BE85E381E5B20E557E46363EF55B0F43B132C2D8E3DE9AC436656F2 0000016b
This can be inserted into the key with
keyctl add trusted kmk "new 32 policy=cat policy.txt keyhandle=0x81000001 hash=sha256" @u
Note that although a few policies work like this, most require special handling which must be added to the kernel policy construction routine.
--- .../security/keys/trusted-encrypted.rst | 16 ++++++ security/keys/trusted-keys/tpm2-policy.c | 53 +++++++++++++++++++ security/keys/trusted-keys/tpm2-policy.h | 1 + security/keys/trusted-keys/trusted_tpm1.c | 15 ++++++ 4 files changed, 85 insertions(+)
Documentation/security/keys/trusted-encrypted.rst +16 -0
@@ -76,6 +76,9 @@ Usage:: policyhandle= handle to an authorization policy session that defines the same policy and with the same hash algorithm as was used to seal the key. + policy= specify an arbitrary set of policies. These must + be in policymaker format with each separate + policy line newline terminated. "keyctl print" returns an ascii hex copy of the sealed key, which is in standard TPM_STORED_DATA format. The key length for new keys are always in bytes.
@@ -168,6 +171,19 @@ zeros (the value of PCR 16):: $ dd if=/dev/zero bs=1 count 2>/dev/null|sha1sum 6768033e216468247bd031a0a2d9876d79818f8f +You can also specify arbitrary policy in policymaker format, so a two +value policy (the pcr example above and authvalue) would look like +this in policymaker format:: + + 0000017F000000010004030000016768033e216468247bd031a0a2d9876d79818f8f + 0000016b + +This can be placed in a file (say policy.txt) and then added to the key as:: + + $ keyctl add trusted kmk "new 32 keyhandle=0x81000001 hash=sha1 policy=`cat policy.txt`" @u + +The newlines in the file policy.txt will be automatically processed. + Reseal a trusted key under new pcr values:: $ keyctl update 268728824 "update pcrinfo=`cat pcr.blob`"
security/keys/trusted-keys/tpm2-policy.c +53 -0
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security/keys/trusted-keys/tpm2-policy.h +1 -0
@@ -28,3 +28,4 @@ int tpm2_generate_policy_digest(struct tpm2_policies *pols, u32 hash,int tpm2_encode_policy (struct tpm2_policies *pols,u8 **data,u32 *len);int tpm2_get_policy_session (struct tpm_chip *chip,struct tpm2_policies *pols,u32 *handle); +int tpm2_parse_policies (struct tpm2_policies **ppols,char *str);
security/keys/trusted-keys/trusted_tpm1.c +15 -0
@@ -29,6 +29,8 @@#include <keys/trusted_tpm.h> +#include "tpm2-policy.h" +static const char hmac_alg[] ="hmac(sha1)" ;static const char hash_alg[] ="sha1" ;static struct tpm_chip *chip;
@@ -709,6 +711,7 @@ enum { Opt_hash, Opt_policydigest, Opt_policyhandle, + Opt_policy, }; static const match_table_t key_tokens = {
@@ -724,6 +727,7 @@ static const match_table_t key_tokens = { {Opt_hash, "hash=%s"}, {Opt_policydigest, "policydigest=%s"}, {Opt_policyhandle, "policyhandle=%s"}, + {Opt_policy, "policy=%s"}, {Opt_err, NULL} };
@@ -854,6 +858,17 @@ static int getoptions(char *c, struct trusted_key_payload *pay,return -EINVAL ; opt->policyhandle = handle;break ; + +case Opt_policy: +if (pay->policies) +return -EINVAL ; +if (!tpm2) +return -EINVAL ; + res =tpm2_parse_policies (&pay->policies, args[0 ].from); +if (res) +return res; +break ; +default :return -EINVAL ; }
Signature · 1 line
2.26.2
James Bottomley
maintainerPATCH v12 3/3 security: keys: trusted: implement counter/timer policy
In reply to James BottomleyThis is actually a generic policy allowing a range of comparisons against any value set in the TPM Clock, which includes things like the reset count, a monotonic millisecond count and the restart count. The most useful comparison is against the millisecond count for expiring keys. However, you have to remember that currently Linux doesn't try to sync the epoch timer with the TPM, so the expiration is actually measured in how long the TPM itself has been powered on ... the TPM timer doesn't count while the system is powered down. The millisecond counter is a u64 quantity found at offset 8 in the timer structure, and the <= comparision operand is 9, so a policy set to expire after the TPM has been up for 100 seconds would look like
0000016d00000000000f424000080009
Where 0x16d is the counter timer policy code and 0xf4240 is 100 000 in hex.
--- .../security/keys/trusted-encrypted.rst | 31 +++++++++++++- include/linux/tpm.h | 1 + security/keys/trusted-keys/tpm2-policy.c | 40 ++++++++++++++++++- security/keys/trusted-keys/trusted_tpm2.c | 36 ++++++++++++++++- 4 files changed, 105 insertions(+), 3 deletions(-)
Documentation/security/keys/trusted-encrypted.rst +30 -1
@@ -242,7 +242,6 @@ Another new format 'enc32' has been defined in order to support encrypted keys with payload size of 32 bytes. This will initially be used for nvdimm security but may expand to other usages that require 32 bytes payload. - TPM 2.0 ASN.1 Key Format ------------------------
@@ -316,3 +315,33 @@ string length. privkey is the binary representation of TPM2B_PUBLIC excluding the initial TPM2B header which can be reconstructed from the ASN.1 octed string length. + + +Appendix +-------- + +TPM 2.0 Policies +---------------- + +The current TPM supports PCR lock policies as documented above and +CounterTimer policies which can be used to create expiring keys. One +caveat with expiring keys is that the TPM millisecond counter does not +update while a system is powered off and Linux does not sync the TPM +millisecond count with its internal clock, so the best you can expire +in is in terms of how long any given TPM has been powered on. (FIXME: +Linux should simply update the millisecond clock to the current number +of seconds past the epoch on boot). + +A CounterTimer policy is expressed in terms of length and offset +against the TPM clock structure (TPMS_TIME_INFO), which looks like the +packed structure:: + + struct tpms_time_info { + u64 uptime; /* time in ms since last start or reset */ + u64 clock; /* cumulative uptime in ms */ + u32 resetcount; /* numer of times the TPM has been reset */ + u32 restartcount; /* number of times the TPM has been restarted */ + u8 safe /* time was safely loaded from NVRam */ + }; + +The usual comparison for expiring keys is against clock, at offset 8.
include/linux/tpm.h +1 -0
@@ -241,6 +241,7 @@ enum tpm2_command_codes {TPM2_CC_PCR_EXTEND =0x0182 ,TPM2_CC_EVENT_SEQUENCE_COMPLETE =0x0185 ,TPM2_CC_HASH_SEQUENCE_START =0x0186 , +TPM2_CC_POLICY_PASSWORD =0x018c ,TPM2_CC_CREATE_LOADED =0x0191 , TPM2_CC_LAST = 0x0193, /* Spec 1.36 */ };
security/keys/trusted-keys/tpm2-policy.c +39 -1
@@ -199,7 +199,8 @@ int tpm2_generate_policy_digest(struct tpm2_policies *pols, len = *plen; } -crypto_shash_update (sdesc, policy, len); +if (len) +crypto_shash_update (sdesc, policy, len);/* now output the intermediate to the policydigest */ crypto_shash_final (sdesc, policydigest);
@@ -334,6 +335,16 @@ int tpm2_get_policy_session(struct tpm_chip *chip, struct tpm2_policies *pols,u32 cmd = pols->code[i];struct tpm_buf buf; +if (cmd =TPM2_CC_POLICY_AUTHVALUE ) +/* +* both PolicyAuthValue and PolicyPassword +* hash to the same thing, but one triggers +* HMAC authentication and the other simple +* authentication. Since we have no HMAC +* code, we're choosing the simple +*/ + cmd =TPM2_CC_POLICY_PASSWORD ; + rc =tpm_buf_init (&buf,TPM2_ST_NO_SESSIONS , cmd);if (rc)return rc;
@@ -354,8 +365,35 @@ int tpm2_get_policy_session(struct tpm_chip *chip, struct tpm2_policies *pols,tpm_buf_append (&buf, pols->policies[i], pols->len[i] - pols->hash_size);break ; + +case TPM2_CC_POLICY_COUNTER_TIMER : { +/* +* the format of this is the last two u16 +* quantities are the offset and operation +* respectively. The rest is operandB which +* must be zero padded in a hash digest +*/ +u16 opb_len = pols->len[i] -4 ; + +if (opb_len > pols->hash_size) +return -EINVAL ; + +tpm_buf_append_u16 (&buf, opb_len); +tpm_buf_append (&buf, pols->policies[i], opb_len); + +/* offset and operand*/ +tpm_buf_append (&buf, pols->policies[i] + opb_len,4 ); + failure ="Counter Timer" ; + +break ; + } +default : failure ="unknown policy" ; +if (pols->len[i]) +tpm_buf_append (&buf, pols->policies[i], + pols->len[i]); +break ; }
security/keys/trusted-keys/trusted_tpm2.c +35 -1
@@ -248,6 +248,7 @@ int tpm2_seal_trusted(struct tpm_chip *chip,u32 flags;int i;int rc; +static const int POLICY_SIZE =2 *PAGE_SIZE ;for (i =0 ; i <ARRAY_SIZE (tpm2_hash_map); i++) {if (options->hash = tpm2_hash_map[i].crypto_id) {
@@ -268,7 +269,7 @@ int tpm2_seal_trusted(struct tpm_chip *chip,/* 4 array len, 2 hash alg */ const int len =4 +2 + options->pcrinfo_len; - pols =kmalloc (sizeof (*pols) + len,GFP_KERNEL ); + pols =kmalloc (POLICY_SIZE ,GFP_KERNEL );if (!pols)return -ENOMEM ;
@@ -289,6 +290,39 @@ int tpm2_seal_trusted(struct tpm_chip *chip,return -EINVAL ; } +/* +* if we already have a policy, we have to add authorization +* to it. If we don't, we can simply follow the usual +* non-policy route. +*/ +if (options->blobauth_len !=0 && payload->policies) { +struct tpm2_policies *pols; +static u8 *scratch; +int i; +bool found = false; + + pols = payload->policies; + +/* make sure it's not already in policy */ +for (i =0 ; i < pols->count; i++) { +if (pols->code[i] =TPM2_CC_POLICY_AUTHVALUE ) { + found = true; + +break ; + } + } + +if (!found) { + i = pols->count++; + scratch = pols->policies[i -1 ] + pols->len[i -1 ]; + +/* the TPM2_PolicyPassword command has no payload */ + pols->policies[i] = scratch; + pols->len[i] =0 ; + pols->code[i] =TPM2_CC_POLICY_AUTHVALUE ; + } + } +if (payload->policies) { rc = tpm2_generate_policy_digest(payload->policies, options->hash,
Signature · 1 line
2.26.2