From: James Bottomley <James.Bottomley@HansenPartnership.com> To: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> Cc: linux-integrity@vger.kernel.org, Mimi Zohar <zohar@linux.ibm.com>, David Woodhouse <dwmw2@infradead.org>, keyrings@vger.kernel.org Subject: Re: [PATCH v6 3/6] security: keys: trusted: fix TPM2 authorizations Date: Tue, 03 Mar 2020 20:39:08 +0000 [thread overview] Message-ID: <1583267948.3638.7.camel@HansenPartnership.com> (raw) In-Reply-To: <20200303193302.GC5775@linux.intel.com> On Tue, 2020-03-03 at 21:33 +0200, Jarkko Sakkinen wrote: > On Mon, Mar 02, 2020 at 07:27:56AM -0500, James Bottomley wrote: > > In TPM 1.2 an authorization was a 20 byte number. The spec > > actually recommended you to hash variable length passwords and use > > the sha1 hash as the authorization. Because the spec doesn't > > require this hashing, the current authorization for trusted keys is > > a 40 digit hex number. For TPM 2.0 the spec allows the passing in > > of variable length passwords and passphrases directly, so we should > > allow that in trusted keys for ease of use. Update the 'blobauth' > > parameter to take this into account, so we can now use plain text > > passwords for the keys. > > > > so before > > > > keyctl add trusted kmk "new 32 > > blobauthõ72d396fae9206628714fb2ce00f72e94f2258f" > > > > after we will accept both the old hex sha1 form as well as a new > > directly supplied password: > > > > keyctl add trusted kmk "new 32 blobauth=hello keyhandle000001" > > > > Since a sha1 hex code must be exactly 40 bytes long and a direct > > password must be 20 or less, we use the length as the discriminator > > for which form is input. > > > > Note this is both and enhancement and a potential bug fix. The TPM > > 2.0 spec requires us to strip leading zeros, meaning empyty > > authorization is a zero length HMAC whereas we're currently passing > > in > > 20 bytes of zeros. A lot of TPMs simply accept this as OK, but the > > Microsoft TPM emulator rejects it with TPM_RC_BAD_AUTH, so this > > patch > > makes the Microsoft TPM emulator work with trusted keys. > > The commit message does not mention it but there limitation that you > cannot have this as a *password*: > > f572d396fae9206628714fb2ce00f72e94f2258f > > The commit message should explicitly state this. Well, that's impossible anyway: the password can be at most TPM_DIGEST_SIZE characters and the above is twice that, so the discriminator is fairly simple: if the string size is less than or equal to TPM_DIGEST_SIZE, then it's a plain password, if it's exactly 2xTPM_DIGEST_SIZE it must be a hex value and if it's anything else, it's illegal. I thought the sentence Since a sha1 hex code must be exactly 40 bytes long and a direct password must be 20 or less, we use the length as the discriminator for which form is input. Was the explanation for this, but I can update it. > > Signed-off-by: James Bottomley > > <James.Bottomley@HansenPartnership.com> > > Fixes: 0fe5480303a1 ("keys, trusted: seal/unseal with TPM 2.0 > > chips") > > Fixes should be before SOB. OK, I'll reverse them. James
WARNING: multiple messages have this Message-ID (diff)
From: James Bottomley <James.Bottomley@HansenPartnership.com> To: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> Cc: linux-integrity@vger.kernel.org, Mimi Zohar <zohar@linux.ibm.com>, David Woodhouse <dwmw2@infradead.org>, keyrings@vger.kernel.org Subject: Re: [PATCH v6 3/6] security: keys: trusted: fix TPM2 authorizations Date: Tue, 03 Mar 2020 15:39:08 -0500 [thread overview] Message-ID: <1583267948.3638.7.camel@HansenPartnership.com> (raw) In-Reply-To: <20200303193302.GC5775@linux.intel.com> On Tue, 2020-03-03 at 21:33 +0200, Jarkko Sakkinen wrote: > On Mon, Mar 02, 2020 at 07:27:56AM -0500, James Bottomley wrote: > > In TPM 1.2 an authorization was a 20 byte number. The spec > > actually recommended you to hash variable length passwords and use > > the sha1 hash as the authorization. Because the spec doesn't > > require this hashing, the current authorization for trusted keys is > > a 40 digit hex number. For TPM 2.0 the spec allows the passing in > > of variable length passwords and passphrases directly, so we should > > allow that in trusted keys for ease of use. Update the 'blobauth' > > parameter to take this into account, so we can now use plain text > > passwords for the keys. > > > > so before > > > > keyctl add trusted kmk "new 32 > > blobauth=f572d396fae9206628714fb2ce00f72e94f2258f" > > > > after we will accept both the old hex sha1 form as well as a new > > directly supplied password: > > > > keyctl add trusted kmk "new 32 blobauth=hello keyhandle=81000001" > > > > Since a sha1 hex code must be exactly 40 bytes long and a direct > > password must be 20 or less, we use the length as the discriminator > > for which form is input. > > > > Note this is both and enhancement and a potential bug fix. The TPM > > 2.0 spec requires us to strip leading zeros, meaning empyty > > authorization is a zero length HMAC whereas we're currently passing > > in > > 20 bytes of zeros. A lot of TPMs simply accept this as OK, but the > > Microsoft TPM emulator rejects it with TPM_RC_BAD_AUTH, so this > > patch > > makes the Microsoft TPM emulator work with trusted keys. > > The commit message does not mention it but there limitation that you > cannot have this as a *password*: > > f572d396fae9206628714fb2ce00f72e94f2258f > > The commit message should explicitly state this. Well, that's impossible anyway: the password can be at most TPM_DIGEST_SIZE characters and the above is twice that, so the discriminator is fairly simple: if the string size is less than or equal to TPM_DIGEST_SIZE, then it's a plain password, if it's exactly 2xTPM_DIGEST_SIZE it must be a hex value and if it's anything else, it's illegal. I thought the sentence Since a sha1 hex code must be exactly 40 bytes long and a direct password must be 20 or less, we use the length as the discriminator for which form is input. Was the explanation for this, but I can update it. > > Signed-off-by: James Bottomley > > <James.Bottomley@HansenPartnership.com> > > Fixes: 0fe5480303a1 ("keys, trusted: seal/unseal with TPM 2.0 > > chips") > > Fixes should be before SOB. OK, I'll reverse them. James
next prev parent reply other threads:[~2020-03-03 20:39 UTC|newest] Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-03-02 12:27 [PATCH v6 0/6] TPM 2.0 trusted keys with attached policy James Bottomley 2020-03-02 12:27 ` James Bottomley 2020-03-02 12:27 ` [PATCH v6 1/6] lib: add ASN.1 encoder James Bottomley 2020-03-02 12:27 ` James Bottomley 2020-03-03 19:22 ` Jarkko Sakkinen 2020-03-03 19:22 ` Jarkko Sakkinen 2020-03-03 20:49 ` James Bottomley 2020-03-03 20:49 ` James Bottomley 2020-03-03 21:31 ` Jarkko Sakkinen 2020-03-03 21:31 ` Jarkko Sakkinen 2020-03-02 12:27 ` [PATCH v6 2/6] oid_registry: Add TCG defined OIDS for TPM keys James Bottomley 2020-03-02 12:27 ` James Bottomley 2020-03-03 19:24 ` Jarkko Sakkinen 2020-03-03 19:24 ` Jarkko Sakkinen 2020-03-02 12:27 ` [PATCH v6 3/6] security: keys: trusted: fix TPM2 authorizations James Bottomley 2020-03-02 12:27 ` James Bottomley 2020-03-03 19:33 ` Jarkko Sakkinen 2020-03-03 19:33 ` Jarkko Sakkinen 2020-03-03 20:39 ` James Bottomley [this message] 2020-03-03 20:39 ` James Bottomley 2020-03-03 21:32 ` Jarkko Sakkinen 2020-03-03 21:32 ` Jarkko Sakkinen 2020-03-02 12:27 ` [PATCH v6 4/6] security: keys: trusted: use ASN.1 TPM2 key format for the blobs James Bottomley 2020-03-02 12:27 ` James Bottomley 2020-03-03 20:06 ` Jarkko Sakkinen 2020-03-03 20:06 ` Jarkko Sakkinen 2020-03-03 20:42 ` James Bottomley 2020-03-03 20:42 ` James Bottomley 2020-03-03 21:20 ` Jarkko Sakkinen 2020-03-03 21:20 ` Jarkko Sakkinen 2020-03-02 12:27 ` [PATCH v6 5/6] security: keys: trusted: add ability to specify arbitrary policy James Bottomley 2020-03-02 12:27 ` James Bottomley 2020-03-02 12:27 ` [PATCH v6 6/6] security: keys: trusted: implement counter/timer policy James Bottomley 2020-03-02 12:27 ` James Bottomley 2020-03-03 20:08 ` Jarkko Sakkinen 2020-03-03 20:08 ` Jarkko Sakkinen 2020-03-03 20:40 ` James Bottomley 2020-03-03 20:40 ` James Bottomley 2020-03-03 21:20 ` Jarkko Sakkinen 2020-03-03 21:20 ` Jarkko Sakkinen
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