Messages in this thread Patch in this message | | | From | Rusty Russell <> | Subject | Re: [PATCH] MODSIGN: Move the magic string to the end of a module and eliminate the search | Date | Mon, 22 Oct 2012 11:36:47 +1030 |
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David Howells <dhowells@redhat.com> writes: > Emit the magic string that indicates a module has a signature after the > signature data instead of before it. This allows module_sig_check() to be > made simpler and faster by the elimination of the search for the magic string. > Instead we just need to do a single memcmp(). > > This works because at the end of the signature data there is the fixed-length > signature information block. This block then falls immediately prior to the > magic number. > >>From the contents of the information block, it is trivial to calculate the size > of the signature data and thus the size of the actual module data.
Meh, I really wanted to separate the module signature locating (my problem) from the decoding and checking (your problem).
If we're going to require such a header, we can simplify further (untested!).
BTW, I'm not convinced your use of bitfields here is portable; it may be portable enough for Linux though.
Cheers, Rusty.
diff --git a/include/linux/module.h b/include/linux/module.h index 7760c6d..bfd1b2d 100644 --- a/include/linux/module.h +++ b/include/linux/module.h @@ -21,9 +21,6 @@ #include <linux/percpu.h> #include <asm/module.h> -/* In stripped ARM and x86-64 modules, ~ is surprisingly rare. */ -#define MODULE_SIG_STRING "~Module signature appended~\n" - /* Not Yet Implemented */ #define MODULE_SUPPORTED_DEVICE(name) @@ -656,4 +653,29 @@ static inline void module_bug_finalize(const Elf_Ehdr *hdr, static inline void module_bug_cleanup(struct module *mod) {} #endif /* CONFIG_GENERIC_BUG */ +#ifdef CONFIG_MODULE_SIG +#define MODULE_SIG_STRING "~Module signature appended~\n" + +/* + * Appended module signature information block. + * + * The constituents of the signature section are, in order: + * + * - Signer's name + * - Key identifier + * - Signature data + * - Information block + */ +struct module_signature { + enum pkey_algo algo : 8; /* Public-key crypto algorithm */ + enum pkey_hash_algo hash : 8; /* Digest algorithm */ + enum pkey_id_type id_type : 8; /* Key identifier type */ + u8 signer_len; /* Length of signer's name */ + u8 key_id_len; /* Length of key identifier */ + u8 __pad[3]; + __be32 sig_len; /* Length of signature data */ + char marker[sizeof(MODULE_SIG_STRING)-1]; +}; +#endif /* CONFIG_MODULE_SIG */ + #endif /* _LINUX_MODULE_H */ diff --git a/kernel/module.c b/kernel/module.c index 6085f5e..254d6a3 100644 --- a/kernel/module.c +++ b/kernel/module.c @@ -2424,14 +2424,17 @@ static int module_sig_check(struct load_info *info, const void *mod, unsigned long *_len) { int err = -ENOKEY; - unsigned long markerlen = sizeof(MODULE_SIG_STRING) - 1; + struct module_signature sig; unsigned long len = *_len; - if (len > markerlen && - memcmp(mod + len - markerlen, MODULE_SIG_STRING, markerlen) == 0) { - /* We truncate the module to discard the signature */ - *_len -= markerlen; - err = mod_verify_sig(mod, _len); + if (len > sizeof(sig)) { + memcpy(&sig, mod + len - sizeof(sig), sizeof(sig)); + + if (!memcmp(sig.marker, MODULE_SIG_STRING, sizeof(sig.marker))) { + /* We truncate the module to discard the signature */ + *_len -= sizeof(sig); + err = mod_verify_sig(mod, &sig, _len); + } } if (!err) { diff --git a/kernel/module_signing.c b/kernel/module_signing.c index d492a23..db8e836 100644 --- a/kernel/module_signing.c +++ b/kernel/module_signing.c @@ -17,26 +17,6 @@ #include "module-internal.h" /* - * Module signature information block. - * - * The constituents of the signature section are, in order: - * - * - Signer's name - * - Key identifier - * - Signature data - * - Information block - */ -struct module_signature { - enum pkey_algo algo : 8; /* Public-key crypto algorithm */ - enum pkey_hash_algo hash : 8; /* Digest algorithm */ - enum pkey_id_type id_type : 8; /* Key identifier type */ - u8 signer_len; /* Length of signer's name */ - u8 key_id_len; /* Length of key identifier */ - u8 __pad[3]; - __be32 sig_len; /* Length of signature data */ -}; - -/* * Digest the module contents. */ static struct public_key_signature *mod_make_digest(enum pkey_hash_algo hash, @@ -183,10 +163,10 @@ static struct key *request_asymmetric_key(const char *signer, size_t signer_len, /* * Verify the signature on a module. */ -int mod_verify_sig(const void *mod, unsigned long *_modlen) +int mod_verify_sig(const void *mod, + const struct module_signature *ms, unsigned long *_modlen) { struct public_key_signature *pks; - struct module_signature ms; struct key *key; const void *sig; size_t modlen = *_modlen, sig_len; @@ -194,44 +174,38 @@ int mod_verify_sig(const void *mod, unsigned long *_modlen) pr_devel("==>%s(,%lu)\n", __func__, modlen); - if (modlen <= sizeof(ms)) - return -EBADMSG; - - memcpy(&ms, mod + (modlen - sizeof(ms)), sizeof(ms)); - modlen -= sizeof(ms); - - sig_len = be32_to_cpu(ms.sig_len); + sig_len = be32_to_cpu(ms->sig_len); if (sig_len >= modlen) return -EBADMSG; modlen -= sig_len; if ((size_t)ms.signer_len + ms.key_id_len >= modlen) return -EBADMSG; - modlen -= (size_t)ms.signer_len + ms.key_id_len; + modlen -= (size_t)ms->signer_len + ms.key_id_len; *_modlen = modlen; sig = mod + modlen; /* For the moment, only support RSA and X.509 identifiers */ - if (ms.algo != PKEY_ALGO_RSA || - ms.id_type != PKEY_ID_X509) + if (ms->algo != PKEY_ALGO_RSA || + ms->id_type != PKEY_ID_X509) return -ENOPKG; - if (ms.hash >= PKEY_HASH__LAST || + if (ms->hash >= PKEY_HASH__LAST || !pkey_hash_algo[ms.hash]) return -ENOPKG; - key = request_asymmetric_key(sig, ms.signer_len, - sig + ms.signer_len, ms.key_id_len); + key = request_asymmetric_key(sig, ms->signer_len, + sig + ms->signer_len, ms->key_id_len); if (IS_ERR(key)) return PTR_ERR(key); - pks = mod_make_digest(ms.hash, mod, modlen); + pks = mod_make_digest(ms->hash, mod, modlen); if (IS_ERR(pks)) { ret = PTR_ERR(pks); goto error_put_key; } - ret = mod_extract_mpi_array(pks, sig + ms.signer_len + ms.key_id_len, + ret = mod_extract_mpi_array(pks, sig + ms->signer_len + ms->key_id_len, sig_len); if (ret < 0) goto error_free_pks;
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