| Message ID | 20210220013255.1083202-6-matthewgarrett@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Enable hibernation when Lockdown is enabled | expand |
On Sat, Feb 20, 2021 at 01:32:51AM +0000, Matthew Garrett wrote: > When TPMs generate keys, they can also generate some information > describing the state of the PCRs at creation time. This data can then > later be certified by the TPM, allowing verification of the PCR values. > This allows us to determine the state of the system at the time a key > was generated. Add an additional argument to the trusted key creation > options, allowing the user to provide the set of PCRs that should have > their values incorporated into the creation data. > > Signed-off-by: Matthew Garrett <mjg59@google.com> LGTM too. Something popped into mind: could we make PCR 23 reservation dynamic instead of a config option. E.g. if the user space uses it, then it's dirty and hibernate will fail. I really dislike the static compilation time firewall on it. /Jarkko
On Sat, Feb 20, 2021 at 05:09:07 +0200, Jarkko Sakkinen wrote: > Something popped into mind: could we make PCR 23 reservation dynamic > instead of a config option. > > E.g. if the user space uses it, then it's dirty and hibernate will > fail. I really dislike the static compilation time firewall on it. I don't know the threat model here, but couldn't hibernation then be blocked by userspace using PCR 23 in some way (thus becoming a Denial of Service)? Are elevated permissions required to use PCR values? --Ben
On Sat, Feb 20, 2021 at 05:09:07AM +0200, Jarkko Sakkinen wrote: > Something popped into mind: could we make PCR 23 reservation dynamic > instead of a config option. > > E.g. if the user space uses it, then it's dirty and hibernate will > fail. I really dislike the static compilation time firewall on it. We can fail hibernation if userland hasn't flagged things, but the concern is that if you hibernate with PCR 23 blocking enabled and then reboot with the blocking disabled, userland can obtain the blob from the hibernation image, extend PCR 23, modify the image and use the key they've recovered to make it look legitimate, enable PCR 23 blocking again and then resume into their own code.
diff --git a/Documentation/security/keys/trusted-encrypted.rst b/Documentation/security/keys/trusted-encrypted.rst index 1da879a68640..27bc43463ec8 100644 --- a/Documentation/security/keys/trusted-encrypted.rst +++ b/Documentation/security/keys/trusted-encrypted.rst @@ -72,6 +72,10 @@ 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. + creationpcrs= hex integer representing the set of PCR values to be + included in the PCR creation data. The bit corresponding + to each PCR should be 1 to be included, 0 to be ignored. + TPM2 only. "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. diff --git a/include/keys/trusted-type.h b/include/keys/trusted-type.h index 154d8a1769c3..875e05f33b84 100644 --- a/include/keys/trusted-type.h +++ b/include/keys/trusted-type.h @@ -47,6 +47,7 @@ struct trusted_key_options { uint32_t policydigest_len; unsigned char policydigest[MAX_DIGEST_SIZE]; uint32_t policyhandle; + uint32_t creation_pcrs; }; extern struct key_type key_type_trusted; diff --git a/security/keys/trusted-keys/trusted_tpm1.c b/security/keys/trusted-keys/trusted_tpm1.c index 74d82093cbaa..3d371ab3441f 100644 --- a/security/keys/trusted-keys/trusted_tpm1.c +++ b/security/keys/trusted-keys/trusted_tpm1.c @@ -709,6 +709,7 @@ enum { Opt_hash, Opt_policydigest, Opt_policyhandle, + Opt_creationpcrs, }; static const match_table_t key_tokens = { @@ -724,6 +725,7 @@ static const match_table_t key_tokens = { {Opt_hash, "hash=%s"}, {Opt_policydigest, "policydigest=%s"}, {Opt_policyhandle, "policyhandle=%s"}, + {Opt_creationpcrs, "creationpcrs=%s"}, {Opt_err, NULL} }; @@ -834,6 +836,13 @@ static int getoptions(char *c, struct trusted_key_payload *pay, return -EINVAL; opt->policyhandle = handle; break; + case Opt_creationpcrs: + if (!tpm2) + return -EINVAL; + res = kstrtoint(args[0].from, 16, &opt->creation_pcrs); + if (res < 0) + return -EINVAL; + break; default: return -EINVAL; } diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c index a3673fffd834..282f956ad610 100644 --- a/security/keys/trusted-keys/trusted_tpm2.c +++ b/security/keys/trusted-keys/trusted_tpm2.c @@ -124,7 +124,7 @@ int tpm2_seal_trusted(struct tpm_chip *chip, unsigned int offset; struct tpm_buf buf; u32 hash; - int i; + int i, j; int rc; for (i = 0; i < ARRAY_SIZE(tpm2_hash_map); i++) { @@ -181,7 +181,28 @@ int tpm2_seal_trusted(struct tpm_chip *chip, tpm_buf_append_u16(&buf, 0); /* creation PCR */ - tpm_buf_append_u32(&buf, 0); + if (options->creation_pcrs) { + /* One bank */ + tpm_buf_append_u32(&buf, 1); + /* Which bank to use */ + tpm_buf_append_u16(&buf, hash); + /* Length of the PCR bitmask */ + tpm_buf_append_u8(&buf, 3); + /* PCR bitmask */ + for (i = 0; i < 3; i++) { + char tmp = 0; + + for (j = 0; j < 8; j++) { + char bit = (i * 8) + j; + + if (options->creation_pcrs & (1 << bit)) + tmp |= (1 << j); + } + tpm_buf_append_u8(&buf, tmp); + } + } else { + tpm_buf_append_u32(&buf, 0); + } if (buf.flags & TPM_BUF_OVERFLOW) { rc = -E2BIG;
When TPMs generate keys, they can also generate some information describing the state of the PCRs at creation time. This data can then later be certified by the TPM, allowing verification of the PCR values. This allows us to determine the state of the system at the time a key was generated. Add an additional argument to the trusted key creation options, allowing the user to provide the set of PCRs that should have their values incorporated into the creation data. Signed-off-by: Matthew Garrett <mjg59@google.com> --- .../security/keys/trusted-encrypted.rst | 4 +++ include/keys/trusted-type.h | 1 + security/keys/trusted-keys/trusted_tpm1.c | 9 +++++++ security/keys/trusted-keys/trusted_tpm2.c | 25 +++++++++++++++++-- 4 files changed, 37 insertions(+), 2 deletions(-)