[PATCH 1/2] efi_loader: add sha384/512 on certificate revocation
AKASHI Takahiro
takahiro.akashi at linaro.org
Tue Apr 19 03:46:43 CEST 2022
Ilias,
On Mon, Apr 18, 2022 at 09:07:22PM +0300, Ilias Apalodimas wrote:
> Currently we don't support sha384/512 for the X.509 certificate
> in dbx. Moreover if we come across such a hash we skip the check
> and approve the image, although the image might needs to be rejected.
>
> Rework the code a bit and fix it by adding an array of structs with the
> supported GUIDs, len and literal used in the U-Boot crypto APIs instead
> of hardcoding the GUID types.
>
> It's worth noting here that efi_hash_regions() can now be reused from
> efi_signature_lookup_digest() and add sha348/512 support there as well
>
> Signed-off-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
> ---
> changes since v2:
> - updated changelog (there was no v1)
> changes since RFC:
> - add an array of structs with the algo info info of a function
> - checking hash_calculate result in efi_hash_regions()
> include/efi_api.h | 6 +++
> include/efi_loader.h | 7 +++
> lib/efi_loader/efi_helper.c | 85 ++++++++++++++++++++++++++++++++++
> lib/efi_loader/efi_signature.c | 76 +++++++++++++++++++++---------
> 4 files changed, 151 insertions(+), 23 deletions(-)
>
> diff --git a/include/efi_api.h b/include/efi_api.h
> index 982c2001728d..b9a04958f9ba 100644
> --- a/include/efi_api.h
> +++ b/include/efi_api.h
> @@ -1873,6 +1873,12 @@ struct efi_system_resource_table {
> #define EFI_CERT_X509_SHA256_GUID \
> EFI_GUID(0x3bd2a492, 0x96c0, 0x4079, 0xb4, 0x20, \
> 0xfc, 0xf9, 0x8e, 0xf1, 0x03, 0xed)
> +#define EFI_CERT_X509_SHA384_GUID \
> + EFI_GUID(0x7076876e, 0x80c2, 0x4ee6, \
> + 0xaa, 0xd2, 0x28, 0xb3, 0x49, 0xa6, 0x86, 0x5b)
> +#define EFI_CERT_X509_SHA512_GUID \
> + EFI_GUID(0x446dbf63, 0x2502, 0x4cda, \
> + 0xbc, 0xfa, 0x24, 0x65, 0xd2, 0xb0, 0xfe, 0x9d)
> #define EFI_CERT_TYPE_PKCS7_GUID \
> EFI_GUID(0x4aafd29d, 0x68df, 0x49ee, 0x8a, 0xa9, \
> 0x34, 0x7d, 0x37, 0x56, 0x65, 0xa7)
> diff --git a/include/efi_loader.h b/include/efi_loader.h
> index af36639ec6a7..ce221ee9317b 100644
> --- a/include/efi_loader.h
> +++ b/include/efi_loader.h
> @@ -300,6 +300,8 @@ extern const efi_guid_t efi_guid_image_security_database;
> extern const efi_guid_t efi_guid_sha256;
> extern const efi_guid_t efi_guid_cert_x509;
> extern const efi_guid_t efi_guid_cert_x509_sha256;
> +extern const efi_guid_t efi_guid_cert_x509_sha384;
> +extern const efi_guid_t efi_guid_cert_x509_sha512;
> extern const efi_guid_t efi_guid_cert_type_pkcs7;
>
> /* GUID of RNG protocol */
> @@ -671,6 +673,11 @@ efi_status_t efi_file_size(struct efi_file_handle *fh, efi_uintn_t *size);
> /* get a device path from a Boot#### option */
> struct efi_device_path *efi_get_dp_from_boot(const efi_guid_t guid);
>
> +/* get len, string (used in u-boot crypto from a guid */
> +const char *guid_to_sha_str(const efi_guid_t *guid);
> +int guid_to_sha_len(const efi_guid_t *guid);
> +int algo_to_len(const char *algo);
> +
> /**
> * efi_size_in_pages() - convert size in bytes to size in pages
> *
> diff --git a/lib/efi_loader/efi_helper.c b/lib/efi_loader/efi_helper.c
> index 802d39ed97b6..c186ba4a3c01 100644
> --- a/lib/efi_loader/efi_helper.c
> +++ b/lib/efi_loader/efi_helper.c
> @@ -92,3 +92,88 @@ err:
> free(var_value);
> return NULL;
> }
> +
> +const struct guid_to_hash_map {
> + efi_guid_t guid;
> + const char algo[32];
> + u32 bits;
> +} guid_to_hash[] = {
> + {
> + EFI_CERT_X509_SHA256_GUID,
> + "sha256",
> + 256,
=> SHA256_SUM_LEN * 8
> + },
> + {
> + EFI_CERT_SHA256_GUID,
> + "sha256",
> + 256,
> + },
> + {
> + EFI_CERT_X509_SHA384_GUID,
> + "sha384",
> + 384,
> + },
> + {
> + EFI_CERT_X509_SHA512_GUID,
> + "sha512",
> + 512,
> + },
> +};
> +
> +#define MAX_GUID_TO_HASH_COUNT ARRAY_SIZE(guid_to_hash)
> +
> +/** guid_to_sha_str - return the sha string e.g "sha256" for a given guid
> + * used on EFI security databases
> + *
> + * @guid: guid to check
> + *
> + * Return: len or 0 if no match is found
> + */
> +const char *guid_to_sha_str(const efi_guid_t *guid)
> +{
> + size_t i;
> +
> + for (i = 0; i < MAX_GUID_TO_HASH_COUNT; i++) {
> + if (!guidcmp(guid, &guid_to_hash[i].guid))
> + return guid_to_hash[i].algo;
> + }
> +
> + return NULL;
> +}
> +
> +/** guid_to_sha_len - return the sha size in bytes for a given guid
> + * used on EFI security databases
> + *
> + * @guid: guid to check
> + *
> + * Return: len or 0 if no match is found
> + */
> +int guid_to_sha_len(const efi_guid_t *guid)
> +{
> + size_t i;
> +
> + for (i = 0; i < MAX_GUID_TO_HASH_COUNT; i++) {
> + if (!guidcmp(guid, &guid_to_hash[i].guid))
> + return guid_to_hash[i].bits / 8;
> + }
> +
> + return 0;
> +}
If we have algo_to_len(), we don't need guid_to_sha_len().
> +
> +/** algo_to_len - return the sha size in bytes for a given string
> + *
> + * @guid: string to check
> + *
> + * Return: len or 0 if no match is found
> + */
> +int algo_to_len(const char *algo)
This function seems to be quite generic and useful for others.
Why not implement it along with hash_calculate() in hash-checksum.c
(without using guid_to_hash[]).
> +{
> + size_t i;
> +
> + for (i = 0; i < MAX_GUID_TO_HASH_COUNT; i++) {
> + if (!strcmp(algo, guid_to_hash[i].algo))
> + return guid_to_hash[i].bits / 8;
> + }
> +
> + return 0;
> +}
> diff --git a/lib/efi_loader/efi_signature.c b/lib/efi_loader/efi_signature.c
> index 79ed077ae7dd..cf01f21b4d04 100644
> --- a/lib/efi_loader/efi_signature.c
> +++ b/lib/efi_loader/efi_signature.c
> @@ -24,6 +24,8 @@ const efi_guid_t efi_guid_sha256 = EFI_CERT_SHA256_GUID;
> const efi_guid_t efi_guid_cert_rsa2048 = EFI_CERT_RSA2048_GUID;
> const efi_guid_t efi_guid_cert_x509 = EFI_CERT_X509_GUID;
> const efi_guid_t efi_guid_cert_x509_sha256 = EFI_CERT_X509_SHA256_GUID;
> +const efi_guid_t efi_guid_cert_x509_sha384 = EFI_CERT_X509_SHA384_GUID;
> +const efi_guid_t efi_guid_cert_x509_sha512 = EFI_CERT_X509_SHA512_GUID;
> const efi_guid_t efi_guid_cert_type_pkcs7 = EFI_CERT_TYPE_PKCS7_GUID;
>
> static u8 pkcs7_hdr[] = {
> @@ -124,23 +126,32 @@ struct pkcs7_message *efi_parse_pkcs7_header(const void *buf,
> * Return: true on success, false on error
> */
> static bool efi_hash_regions(struct image_region *regs, int count,
> - void **hash, size_t *size)
> + void **hash, const char *hash_algo, int *len)
> {
> + int ret;
> +
> + if (!hash_algo || !len)
> + return false;
> +
> + *len = algo_to_len(hash_algo);
Please modify it this way;
int hash_len;
hash_len = algo_to_len(hash_algo);
if (len)
*len = hash_len;
Then use hash_len instead of *len hereafterr.
This way, we don't have to define a unused local variable below code.
> + if (!*len)
> + return false;
> +
> if (!*hash) {
> - *hash = calloc(1, SHA256_SUM_LEN);
> + *hash = calloc(1, *len);
> if (!*hash) {
> EFI_PRINT("Out of memory\n");
> return false;
> }
> }
> - if (size)
> - *size = SHA256_SUM_LEN;
>
> - hash_calculate("sha256", regs, count, *hash);
> + ret = hash_calculate(hash_algo, regs, count, *hash);
> + if (ret)
> + return false;
> #ifdef DEBUG
> EFI_PRINT("hash calculated:\n");
> print_hex_dump(" ", DUMP_PREFIX_OFFSET, 16, 1,
> - *hash, SHA256_SUM_LEN, false);
> + *hash, *len, false);
> #endif
>
> return true;
> @@ -190,7 +201,6 @@ bool efi_signature_lookup_digest(struct efi_image_regions *regs,
> struct efi_signature_store *siglist;
> struct efi_sig_data *sig_data;
> void *hash = NULL;
> - size_t size = 0;
> bool found = false;
> bool hash_done = false;
>
> @@ -200,6 +210,8 @@ bool efi_signature_lookup_digest(struct efi_image_regions *regs,
> goto out;
>
> for (siglist = db; siglist; siglist = siglist->next) {
> + int len = 0;
> + const char *hash_algo = NULL;
> /*
> * if the hash algorithm is unsupported and we get an entry in
> * dbx reject the image
> @@ -215,8 +227,14 @@ bool efi_signature_lookup_digest(struct efi_image_regions *regs,
> if (guidcmp(&siglist->sig_type, &efi_guid_sha256))
> continue;
>
> + hash_algo = guid_to_sha_str(&efi_guid_sha256);
> + /*
> + * We could check size and hash_algo but efi_hash_regions()
> + * will do that for us
> + */
> if (!hash_done &&
> - !efi_hash_regions(regs->reg, regs->num, &hash, &size)) {
> + !efi_hash_regions(regs->reg, regs->num, &hash, hash_algo,
> + &len)) {
> EFI_PRINT("Digesting an image failed\n");
> break;
> }
> @@ -229,8 +247,8 @@ bool efi_signature_lookup_digest(struct efi_image_regions *regs,
> print_hex_dump(" ", DUMP_PREFIX_OFFSET, 16, 1,
> sig_data->data, sig_data->size, false);
> #endif
> - if (sig_data->size == size &&
> - !memcmp(sig_data->data, hash, size)) {
> + if (sig_data->size == len &&
> + !memcmp(sig_data->data, hash, len)) {
> found = true;
> free(hash);
> goto out;
> @@ -263,8 +281,9 @@ static bool efi_lookup_certificate(struct x509_certificate *cert,
> struct efi_sig_data *sig_data;
> struct image_region reg[1];
> void *hash = NULL, *hash_tmp = NULL;
> - size_t size = 0;
> + int len = 0;
> bool found = false;
> + const char *hash_algo = NULL;
>
> EFI_PRINT("%s: Enter, %p, %p\n", __func__, cert, db);
>
> @@ -278,7 +297,11 @@ static bool efi_lookup_certificate(struct x509_certificate *cert,
> /* calculate hash of TBSCertificate */
> reg[0].data = cert->tbs;
> reg[0].size = cert->tbs_size;
> - if (!efi_hash_regions(reg, 1, &hash, &size))
> +
> + /* We just need any sha256 algo to start the matching */
> + hash_algo = guid_to_sha_str(&efi_guid_sha256);
Why not check if hash_algo is NULL?
> + len = guid_to_sha_len(&efi_guid_sha256);
=> len = algo_to_len(hash_algo);
Or even we don't need this line as efi_has_regions() will set it for us.
> + if (!efi_hash_regions(reg, 1, &hash, hash_algo, &len))
> goto out;
>
> EFI_PRINT("%s: searching for %s\n", __func__, cert->subject);
> @@ -290,6 +313,7 @@ static bool efi_lookup_certificate(struct x509_certificate *cert,
> for (sig_data = siglist->sig_data_list; sig_data;
> sig_data = sig_data->next) {
> struct x509_certificate *cert_tmp;
> + int len_tmp;
We don't need len_tmp if the change I mentioned above is made.
# we don't want to define a unused variable.
> cert_tmp = x509_cert_parse(sig_data->data,
> sig_data->size);
> @@ -300,12 +324,13 @@ static bool efi_lookup_certificate(struct x509_certificate *cert,
> cert_tmp->subject);
> reg[0].data = cert_tmp->tbs;
> reg[0].size = cert_tmp->tbs_size;
> - if (!efi_hash_regions(reg, 1, &hash_tmp, NULL))
> + if (!efi_hash_regions(reg, 1, &hash_tmp, hash_algo,
> + &len_tmp))
=> NULL
> goto out;
>
> x509_free_certificate(cert_tmp);
>
> - if (!memcmp(hash, hash_tmp, size)) {
> + if (!memcmp(hash, hash_tmp, len)) {
> found = true;
> goto out;
> }
> @@ -400,9 +425,10 @@ static bool efi_signature_check_revocation(struct pkcs7_signed_info *sinfo,
> struct efi_sig_data *sig_data;
> struct image_region reg[1];
> void *hash = NULL;
> - size_t size = 0;
> + int len = 0;
> time64_t revoc_time;
> bool revoked = false;
> + const char *hash_algo = NULL;
>
> EFI_PRINT("%s: Enter, %p, %p, %p\n", __func__, sinfo, cert, dbx);
>
> @@ -411,13 +437,14 @@ static bool efi_signature_check_revocation(struct pkcs7_signed_info *sinfo,
>
> EFI_PRINT("Checking revocation against %s\n", cert->subject);
> for (siglist = dbx; siglist; siglist = siglist->next) {
> - if (guidcmp(&siglist->sig_type, &efi_guid_cert_x509_sha256))
> + hash_algo = guid_to_sha_str(&siglist->sig_type);
> + if (!hash_algo)
> continue;
>
> /* calculate hash of TBSCertificate */
> reg[0].data = cert->tbs;
> reg[0].size = cert->tbs_size;
> - if (!efi_hash_regions(reg, 1, &hash, &size))
> + if (!efi_hash_regions(reg, 1, &hash, hash_algo, &len))
> goto out;
>
> for (sig_data = siglist->sig_data_list; sig_data;
> @@ -429,18 +456,18 @@ static bool efi_signature_check_revocation(struct pkcs7_signed_info *sinfo,
> * };
> */
> #ifdef DEBUG
> - if (sig_data->size >= size) {
> + if (sig_data->size >= len) {
> EFI_PRINT("hash in db:\n");
> print_hex_dump(" ", DUMP_PREFIX_OFFSET,
> 16, 1,
> - sig_data->data, size, false);
> + sig_data->data, len, false);
> }
> #endif
> - if ((sig_data->size < size + sizeof(time64_t)) ||
> - memcmp(sig_data->data, hash, size))
> + if ((sig_data->size < len + sizeof(time64_t)) ||
> + memcmp(sig_data->data, hash, len))
> continue;
>
> - memcpy(&revoc_time, sig_data->data + size,
> + memcpy(&revoc_time, sig_data->data + len,
> sizeof(revoc_time));
> EFI_PRINT("revocation time: 0x%llx\n", revoc_time);
> /*
> @@ -488,6 +515,7 @@ bool efi_signature_verify(struct efi_image_regions *regs,
> goto out;
>
> for (sinfo = msg->signed_infos; sinfo; sinfo = sinfo->next) {
> + int len;
ditto
> EFI_PRINT("Signed Info: digest algo: %s, pkey algo: %s\n",
> sinfo->sig->hash_algo, sinfo->sig->pkey_algo);
>
> @@ -500,7 +528,9 @@ bool efi_signature_verify(struct efi_image_regions *regs,
> */
> if (!msg->data &&
> !efi_hash_regions(regs->reg, regs->num,
> - (void **)&sinfo->sig->digest, NULL)) {
> + (void **)&sinfo->sig->digest,
> + guid_to_sha_str(&efi_guid_sha256),
> + &len)) {
=> NULL
-Takahiro Akashi
> EFI_PRINT("Digesting an image failed\n");
> goto out;
> }
> --
> 2.32.0
>
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