diff --git a/Documentation/devicetree/bindings/barebox/barebox,state.rst b/Documentation/devicetree/bindings/barebox/barebox,state.rst index 4c5b06d..ef66029 100644 --- a/Documentation/devicetree/bindings/barebox/barebox,state.rst +++ b/Documentation/devicetree/bindings/barebox/barebox,state.rst @@ -32,6 +32,12 @@ * ``backend``: describes where the data for this state is stored * ``backend-type``: should be ``raw`` or ``dtb``. +Optional properties: + +* ``algo``: A HMAC algorithm used to detect manipulation of the data + or header, sensible values follow this pattern ``hmac()``, + e.g. ``hmac(sha256)``. + Variable nodes -------------- @@ -105,6 +111,19 @@ the actual values of the variables. Unlike the raw state backend the dtb state backend can describe itself. +HMAC +---- + +With the optional property ``algo = "hmac()";`` a HMAC algorithm +can be defined to detect unauthorized modification of the state's +header and/or data. For this to work the HMAC and the selected hash +algorithm have to be compiled into barebox. + +The shared secret for the HMAC is requested via +``keystore_get_secret()``, using the state's name, from the barebox +simple keystore. It's up to the developer to populate the keystore via +``keystore_set_secret()`` in beforehand. + Frontend -------- diff --git a/common/Kconfig b/common/Kconfig index 877d385..8e79509 100644 --- a/common/Kconfig +++ b/common/Kconfig @@ -751,6 +751,24 @@ select OFTREE select PARAMETER +config STATE_CRYPTO + bool "HMAC based authentication support" + depends on STATE + select CRYPTO_KEYSTORE + select DIGEST + select DIGEST_HMAC_GENERIC + help + This options enables HMAC based authentication support for + the state's header and data. This means the state framework + can verify both the data integrity and the authentication of + the state's header and data. + + Don't forget to select a hash algorithm in the + crypto/digests menu. + + See Documentation/devicetree/bindings/barebox/barebox,state.rst + for more information. + config RESET_SOURCE bool "detect Reset cause" depends on GLOBALVAR diff --git a/common/state.c b/common/state.c index d37f4ab..0a9204e 100644 --- a/common/state.c +++ b/common/state.c @@ -15,6 +15,7 @@ */ #include +#include #include #include #include @@ -28,6 +29,8 @@ #include #include +#include + #include #include #include @@ -41,7 +44,7 @@ struct state { struct device_d dev; - const struct device_node *root; + struct device_node *root; struct list_head variables; const char *name; struct list_head list; @@ -55,6 +58,7 @@ const char *name; const char *of_path; const char *path; + struct digest *digest; }; enum state_variable_type { @@ -948,6 +952,16 @@ if (ret) goto out; + if (state->backend->digest) { + p = of_new_property(new_node, "algo", + digest_name(state->backend->digest), + strlen(digest_name(state->backend->digest)) + 1); + if (!p) { + ret = -ENOMEM; + goto out; + } + } + /* address-cells + size-cells */ ret = of_property_write_u32(new_node, "#address-cells", 1); if (ret) @@ -1230,7 +1244,7 @@ struct state_backend_raw { struct state_backend backend; unsigned long size_data; /* The raw data size (without header) */ - unsigned long size_full; /* The size header + raw data */ + unsigned long size_full; /* The size header + raw data + hmac */ unsigned long stride; /* The stride size in bytes of the copies */ off_t offset; /* offset in the storage file */ size_t size; /* size of the storage area */ @@ -1253,8 +1267,9 @@ struct state_variable *sv; struct backend_raw_header header = {}; unsigned long max_len; + int d_len = 0; int ret; - void *buf, *data; + void *buf, *data, *hmac; max_len = backend_raw->stride; @@ -1285,6 +1300,11 @@ return -EINVAL; } + if (backend_raw->backend.digest) { + d_len = digest_length(backend_raw->backend.digest); + max_len -= d_len; + } + if (header.data_len > max_len) { dev_err(&state->dev, "invalid data_len %u in header, max is %lu\n", @@ -1292,14 +1312,15 @@ return -EINVAL; } - buf = xzalloc(sizeof(header) + header.data_len); + buf = xzalloc(sizeof(header) + header.data_len + d_len); data = buf + sizeof(header); + hmac = data + header.data_len; ret = lseek(fd, offset, SEEK_SET); if (ret < 0) goto out_free; - ret = read_full(fd, buf, sizeof(header) + header.data_len); + ret = read_full(fd, buf, sizeof(header) + header.data_len + d_len); if (ret < 0) goto out_free; @@ -1312,6 +1333,23 @@ goto out_free; } + if (backend_raw->backend.digest) { + struct digest *d = backend_raw->backend.digest; + + ret = digest_init(d); + if (ret) + goto out_free; + + /* hmac over header and data */ + ret = digest_update(d, buf, sizeof(header) + header.data_len); + if (ret) + goto out_free; + + ret = digest_verify(d, hmac); + if (ret < 0) + goto out_free; + } + list_for_each_entry(sv, &state->variables, list) { if (sv->start + sv->size > header.data_len) break; @@ -1392,7 +1430,7 @@ struct state_backend_raw *backend_raw = container_of(backend, struct state_backend_raw, backend); int ret = 0, fd, i; - void *buf, *data; + void *buf, *data, *hmac; struct backend_raw_header *header; struct state_variable *sv; @@ -1400,6 +1438,7 @@ header = buf; data = buf + sizeof(*header); + hmac = data + backend_raw->size_data; list_for_each_entry(sv, &state->variables, list) memcpy(data + sv->start, sv->raw, sv->size); @@ -1410,6 +1449,23 @@ header->header_crc = crc32(0, header, sizeof(*header) - sizeof(uint32_t)); + if (backend_raw->backend.digest) { + struct digest *d = backend_raw->backend.digest; + + ret = digest_init(d); + if (ret) + goto out_free; + + /* hmac over header and data */ + ret = digest_update(d, buf, sizeof(*header) + backend_raw->size_data); + if (ret) + goto out_free; + + ret = digest_final(d, hmac); + if (ret < 0) + goto out_free; + } + fd = open(backend->path, O_WRONLY); if (fd < 0) goto out_free; @@ -1494,6 +1550,53 @@ return ret; } +static int state_backend_raw_file_init_digest(struct state *state, struct state_backend_raw *backend_raw) +{ + struct digest *digest; + struct property *p; + const char *algo; + const unsigned char *key; + int key_len, ret; + + p = of_find_property(state->root, "algo", NULL); + if (!p) /* does not exist */ + return 0; + + if (!IS_ENABLED(CONFIG_STATE_CRYPTO)) { + dev_err(&state->dev, + "algo %s specified, but crypto support for state framework (CONFIG_STATE_CRYPTO) not enabled.\n", + algo); + return -EINVAL; + } + + ret = of_property_read_string(state->root, "algo", &algo); + if (ret) + return ret; + + ret = keystore_get_secret(state->name, &key, &key_len); + if (ret == -ENOENT) /* -ENOENT == does not exist */ + return -EPROBE_DEFER; + else if (ret) + return ret; + + digest = digest_alloc(algo); + if (!digest) { + dev_info(&state->dev, "algo %s not found - probe deferred\n", algo); + return -EPROBE_DEFER; + } + + ret = digest_set_key(digest, key, key_len); + if (ret) { + digest_free(digest); + return ret; + } + + backend_raw->backend.digest = digest; + backend_raw->size_full = digest_length(digest); + + return 0; +} + /* * state_backend_raw_file - create a raw file backend store for a state instance * @@ -1534,8 +1637,14 @@ return -EINVAL; backend_raw = xzalloc(sizeof(*backend_raw)); - backend = &backend_raw->backend; + ret = state_backend_raw_file_init_digest(state, backend_raw); + if (ret) { + free(backend_raw); + return ret; + } + + backend = &backend_raw->backend; backend->save = state_backend_raw_save; backend->of_path = xstrdup(of_path); backend->path = xstrdup(path); @@ -1545,7 +1654,7 @@ backend_raw->size_data = sv->start + sv->size; backend_raw->offset = offset; backend_raw->size = size; - backend_raw->size_full = backend_raw->size_data + + backend_raw->size_full += backend_raw->size_data + sizeof(struct backend_raw_header); state->backend = backend; @@ -1581,6 +1690,8 @@ /* ignore return value of load() */ return 0; err: + digest_free(backend_raw->backend.digest); + free(backend_raw); return ret; }