diff options
| -rw-r--r-- | utility/mount-encrypted.c | 120 |
1 files changed, 82 insertions, 38 deletions
diff --git a/utility/mount-encrypted.c b/utility/mount-encrypted.c index e67f7df3..2c0fa8b2 100644 --- a/utility/mount-encrypted.c +++ b/utility/mount-encrypted.c @@ -249,14 +249,34 @@ _read_nvram(uint8_t *buffer, size_t len, uint32_t index, uint32_t size) } /* - * Cases: - * - no NVRAM area at all (OOBE) - * - defined NVRAM area, but TPM not Owned - * - defined NVRAM area, but not Finalized - * - legacy NVRAM area (migration needed) - * - modern NVRAM area (\o/) + * TPM ownership cases: + * - unowned (OOBE): + * - expect modern lockbox (no migration allowed). + * - owned: depends on NVRAM area (below). + * + * NVRAM area cases: + * - no NVRAM area at all: + * - if cr48, assume this is going to always be missing the lockbox: + * - expect no lockbox (migration allowed). + * - otherwise, assume an interrupted install + * - expect modern lockbox (no migration allowed). + * - defined NVRAM area, but not written to ("Finalized"); interrupted OOBE: + * - if legacy size, allow migration. + * - if not, disallow migration. + * - written ("Finalized") NVRAM area: + * - if legacy size, allow migration. + * - if not, disallow migration. + * + * When returning 1: (NVRAM area found and used) + * - *digest populated with NVRAM area entropy. + * - *old_lockbox indicates which lockbox NVRAM area type was used. + * - *static_key will always be 0. + * When returning 0: (NVRAM missing or error) + * - *digest untouched. + * - *old_lockbox indicates future expected lockbox size (after Finalize). + * - *static_key=1 only if TPM owned, lockbox missing, and device is cr48. */ -static int get_nvram_key(uint8_t *digest, int *old_lockbox) +static int get_nvram_key(uint8_t *digest, int *old_lockbox, int *static_key) { uint8_t owned = 0; uint8_t value[kLockboxSizeV2], bytes_anded, bytes_ored; @@ -264,6 +284,21 @@ static int get_nvram_key(uint8_t *digest, int *old_lockbox) uint8_t *rand_bytes; uint32_t rand_size; + /* Expect to use a new lockbox by default, and require NVRAM key. */ + *old_lockbox = 0; + *static_key = 0; + + /* Ignore unowned TPM's NVRAM area. */ + result = tpm_owned(&owned); + if (result != TPM_SUCCESS) { + INFO("Could not read TPM Permanent Flags."); + return 0; + } + if (!owned) { + INFO("TPM not Owned, ignoring NVRAM area."); + return 0; + } + /* Reading the NVRAM takes 40ms. Instead of querying the NVRAM area * for its size (which takes time), just read the expected size. If * it fails, then fall back to the older size. This means cleared @@ -272,7 +307,6 @@ static int get_nvram_key(uint8_t *digest, int *old_lockbox) * which is the minimum possible time (instead of 40ms + time to * query NVRAM size). */ - *old_lockbox = 0; size = kLockboxSizeV2; result = _read_nvram(value, sizeof(value), kLockboxIndex, size); if (result != TPM_SUCCESS) { @@ -281,6 +315,21 @@ static int get_nvram_key(uint8_t *digest, int *old_lockbox) if (result != TPM_SUCCESS) { /* No NVRAM area at all. */ INFO("No NVRAM area defined."); + + /* TPM is owned, without an NVRAM area. If this is a + * Cr48, mark this as using an old NVRAM area to + * allow migration, and mark this as an ancient + * install that did not even know to create a lockbox + * at all. If this is actually a Cr48 that has had + * its OOBE interrupted at the perfect moment, then + * the user is going to lose their settings. This + * should be extremely rare. + */ + if (is_cr48()) { + *static_key = 1; + *old_lockbox = 1; + } + return 0; } /* Legacy NVRAM area. */ @@ -292,21 +341,6 @@ static int get_nvram_key(uint8_t *digest, int *old_lockbox) debug_dump_hex("nvram", value, size); - /* Ignore defined but unowned NVRAM area. */ - /* TODO(keescook): remove this check (it adds 40ms) once the - * NVRAM area is bound to owner so that it will be wiped out - * across device mode changes. - */ - result = tpm_owned(&owned); - if (result != TPM_SUCCESS) { - INFO("Could not read TPM Permanent Flags."); - return 0; - } - if (!owned) { - INFO("TPM not Owned, ignoring NVRAM area."); - return 0; - } - /* Ignore defined but unwritten NVRAM area. */ bytes_ored = 0x0; bytes_anded = 0xff; @@ -344,9 +378,9 @@ static int get_nvram_key(uint8_t *digest, int *old_lockbox) } /* Find the system key used for decrypting the stored encryption key. - * ChromeOS devices are required to use the NVRAM area (excepting CR-48s), - * all the rest will fallback through various places (kernel command line, - * BIOS UUID, and finally a static value) for a system key. + * ChromeOS devices are required to use the NVRAM area, all the rest will + * fallback through various places (kernel command line, BIOS UUID, and + * finally a static value) for a system key. */ static int find_system_key(int mode, uint8_t *digest, int *migration_allowed) { @@ -368,17 +402,25 @@ static int find_system_key(int mode, uint8_t *digest, int *migration_allowed) * NVRAM. */ if (has_chromefw()) { - int rc; - rc = get_nvram_key(digest, migration_allowed); + int rc, static_key = 0; + rc = get_nvram_key(digest, migration_allowed, &static_key); - /* Since the CR-48 did not ship with a lockbox area, they - * are allowed to fall back to non-NVRAM system keys. - */ - if (rc || !is_cr48()) { - INFO("Using NVRAM as system key; %s.", - rc ? "already populated" - : "needs population"); + if (rc) { + /* Use populated NVRAM area. */ + INFO("Using NVRAM as system key; already populated%s.", + migration_allowed ? " (legacy)" : ""); return rc; + } else { + if (!static_key) { + INFO("Using NVRAM as system key; area needed."); + return rc; + } + /* If a static key is allowed, it means the TPM is + * already owned, is missing the NVRAM area, and is + * running on a Cr48. In this special case, fall + * through to the other key methods below, since + * the NVRAM area will never be populated. + */ } } @@ -1027,6 +1069,7 @@ static int report_info(void) uint8_t owned = 0; struct bind_mount *mnt; int old_lockbox = -1; + int static_key = -1; printf("TPM: %s\n", has_tpm ? "yes" : "no"); if (has_tpm) { @@ -1037,11 +1080,12 @@ static int report_info(void) printf("CR48: %s\n", is_cr48() ? "yes" : "no"); if (has_chromefw()) { int rc; - rc = get_nvram_key(system_key, &old_lockbox); + rc = get_nvram_key(system_key, &old_lockbox, &static_key); if (!rc) - printf("NVRAM: missing\n"); + printf("NVRAM: missing%s.\n", + static_key ? " (static key allowed)" : ""); else { - printf("NVRAM: %s, %s\n", + printf("NVRAM: %s, %s.\n", old_lockbox ? "legacy" : "modern", rc ? "available" : "ignored"); } |