75 lines
3.0 KiB
Diff
75 lines
3.0 KiB
Diff
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From fd901d06e52786cfb2bd67919c72d05eab5a4c65 Mon Sep 17 00:00:00 2001
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From: Dan Streetman <ddstreet@ieee.org>
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Date: Sat, 15 Jul 2023 08:30:40 -0400
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Subject: [PATCH] tpm2: add tpm2_get_pin_auth()
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Add function to calculate the hash digest for a provided pin, and also verify
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that the final byte in the digest is not 0. This is required because the TPM
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will always remove all trailing 0's from an auth value before using it.
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Fixes: #27716
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(cherry picked from commit f230572f56a34fd7269c5fda4fb92be5ee0ea281)
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Related: RHEL-16182
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---
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src/shared/tpm2-util.c | 32 ++++++++++++++++++++++++++++++--
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1 file changed, 30 insertions(+), 2 deletions(-)
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diff --git a/src/shared/tpm2-util.c b/src/shared/tpm2-util.c
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index cb05b2a01c..49e50a83ac 100644
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--- a/src/shared/tpm2-util.c
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+++ b/src/shared/tpm2-util.c
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@@ -2795,6 +2795,34 @@ int tpm2_digest_many_digests(
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return tpm2_digest_many(alg, digest, iovecs, n_data, extend);
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}
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+/* This hashes the provided pin into a digest value, but also verifies that the final byte is not 0, because
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+ * the TPM specification Part 1 ("Architecture") section Authorization Values (subsection "Authorization Size
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+ * Convention") states "Trailing octets of zero are to be removed from any string before it is used as an
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+ * authValue". Since the TPM doesn't know if the auth value is a "string" or just a hash digest, any hash
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+ * digest that randomly happens to end in 0 must have the final 0 changed, or the TPM will remove it before
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+ * using the value in its HMAC calculations, resulting in failed HMAC checks. */
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+static int tpm2_get_pin_auth(TPMI_ALG_HASH hash, const char *pin, TPM2B_AUTH *ret_auth) {
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+ TPM2B_AUTH auth = {};
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+ int r;
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+
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+ assert(pin);
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+ assert(ret_auth);
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+
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+ r = tpm2_digest_buffer(hash, &auth, pin, strlen(pin), /* extend= */ false);
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+ if (r < 0)
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+ return r;
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+
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+ assert(auth.size > 0);
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+ if (auth.buffer[auth.size - 1] == 0) {
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+ log_debug("authValue digest ends in 0 which the TPM will remove and cause HMAC authorization failures, adjusting.");
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+ auth.buffer[auth.size - 1] = 0xff;
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+ }
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+
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+ *ret_auth = TAKE_STRUCT(auth);
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+
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+ return 0;
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+}
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+
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static int tpm2_set_auth(Tpm2Context *c, const Tpm2Handle *handle, const char *pin) {
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TPM2B_AUTH auth = {};
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TSS2_RC rc;
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@@ -2808,7 +2836,7 @@ static int tpm2_set_auth(Tpm2Context *c, const Tpm2Handle *handle, const char *p
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CLEANUP_ERASE(auth);
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- r = tpm2_digest_buffer(TPM2_ALG_SHA256, &auth, pin, strlen(pin), /* extend= */ false);
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+ r = tpm2_get_pin_auth(TPM2_ALG_SHA256, pin, &auth);
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if (r < 0)
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return r;
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@@ -3955,7 +3983,7 @@ int tpm2_seal(Tpm2Context *c,
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CLEANUP_ERASE(hmac_sensitive);
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if (pin) {
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- r = tpm2_digest_buffer(TPM2_ALG_SHA256, &hmac_sensitive.userAuth, pin, strlen(pin), /* extend= */ false);
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+ r = tpm2_get_pin_auth(TPM2_ALG_SHA256, pin, &hmac_sensitive.userAuth);
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if (r < 0)
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return r;
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}
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