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efi_loader: image_loader: add digest-based verification for signed image

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In case that a type of certificate in "db" or "dbx" is
EFI_CERT_X509_SHA256_GUID, it is actually not a certificate which contains
a public key for RSA decryption, but a digest of image to be loaded.
If the value matches to a value calculated from a given binary image, it is
granted for loading.

With this patch, common digest check code, which used to be used for
unsigned image verification, will be extracted from
efi_signature_verify_with_sigdb() into efi_signature_lookup_digest(), and
extra step for digest check will be added to efi_image_authenticate().

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
This commit is contained in:
AKASHI Takahiro 2020-07-08 14:01:57 +09:00 committed by Heinrich Schuchardt
parent 11bafb2596
commit 7926dfb579
3 changed files with 102 additions and 78 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/efi_loader.h
View File

@ -765,6 +765,8 @@ struct efi_signature_store {
struct x509_certificate;
struct pkcs7_message;
bool efi_signature_lookup_digest(struct efi_image_regions *regs,
struct efi_signature_store *db);
bool efi_signature_verify_one(struct efi_image_regions *regs,
struct pkcs7_message *msg,
struct efi_signature_store *db);

44
lib/efi_loader/efi_image_loader.c
View File

@ -448,16 +448,16 @@ static bool efi_image_unsigned_authenticate(struct efi_image_regions *regs)
}
/* try black-list first */
if (efi_signature_verify_one(regs, NULL, dbx)) {
EFI_PRINT("Image is not signed and rejected by \"dbx\"\n");
if (efi_signature_lookup_digest(regs, dbx)) {
EFI_PRINT("Image is not signed and its digest found in \"dbx\"\n");
goto out;
}
/* try white-list */
if (efi_signature_verify_one(regs, NULL, db))
if (efi_signature_lookup_digest(regs, db))
ret = true;
else
EFI_PRINT("Image is not signed and not found in \"db\" or \"dbx\"\n");
EFI_PRINT("Image is not signed and its digest not found in \"db\" or \"dbx\"\n");
out:
efi_sigstore_free(db);
@ -605,6 +605,25 @@ static bool efi_image_authenticate(void *efi, size_t efi_size)
continue;
}
/*
* NOTE:
* UEFI specification defines two signature types possible
* in signature database:
* a. x509 certificate, where a signature in image is
* a message digest encrypted by RSA public key
* (EFI_CERT_X509_GUID)
* b. bare hash value of message digest
* (EFI_CERT_SHAxxx_GUID)
*
* efi_signature_verify() handles case (a), while
* efi_signature_lookup_digest() handles case (b).
*
* There is a third type:
* c. message digest of a certificate
* (EFI_CERT_X509_SHAAxxx_GUID)
* This type of signature is used only in revocation list
* (dbx) and handled as part of efi_signatgure_verify().
*/
/* try black-list first */
if (efi_signature_verify_one(regs, msg, dbx)) {
EFI_PRINT("Signature was rejected by \"dbx\"\n");
@ -616,11 +635,22 @@ static bool efi_image_authenticate(void *efi, size_t efi_size)
goto err;
}
/* try white-list */
if (!efi_signature_verify_with_sigdb(regs, msg, db, dbx)) {
EFI_PRINT("Signature was not verified by \"db\"\n");
if (efi_signature_lookup_digest(regs, dbx)) {
EFI_PRINT("Image's digest was found in \"dbx\"\n");
goto err;
}
/* try white-list */
if (efi_signature_verify_with_sigdb(regs, msg, db, dbx))
continue;
debug("Signature was not verified by \"db\"\n");
if (efi_signature_lookup_digest(regs, db))
continue;
debug("Image's digest was not found in \"db\" or \"dbx\"\n");
goto err;
}
ret = true;

134
lib/efi_loader/efi_signature.c
View File

@ -197,6 +197,68 @@ out:
return verified;
}
/**
* efi_signature_lookup_digest - search for an image's digest in sigdb
* @regs: List of regions to be authenticated
* @db: Signature database for trusted certificates
*
* A message digest of image pointed to by @regs is calculated and
* its hash value is compared to entries in signature database pointed
* to by @db.
*
* Return: true if found, false if not
*/
bool efi_signature_lookup_digest(struct efi_image_regions *regs,
struct efi_signature_store *db)
{
struct efi_signature_store *siglist;
struct efi_sig_data *sig_data;
void *hash = NULL;
size_t size = 0;
bool found = false;
EFI_PRINT("%s: Enter, %p, %p\n", __func__, regs, db);
if (!regs || !db || !db->sig_data_list)
goto out;
for (siglist = db; siglist; siglist = siglist->next) {
/* TODO: support other hash algorithms */
if (guidcmp(&siglist->sig_type, &efi_guid_sha256)) {
EFI_PRINT("Digest algorithm is not supported: %pUl\n",
&siglist->sig_type);
break;
}
if (!efi_hash_regions(regs->reg, regs->num, &hash, &size)) {
EFI_PRINT("Digesting an image failed\n");
break;
}
for (sig_data = siglist->sig_data_list; sig_data;
sig_data = sig_data->next) {
#ifdef DEBUG
EFI_PRINT("Msg digest in database:\n");
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)) {
found = true;
free(hash);
goto out;
}
}
free(hash);
hash = NULL;
}
out:
EFI_PRINT("%s: Exit, found: %d\n", __func__, found);
return found;
}
/**
* efi_signature_verify_with_list - verify a signature with signature list
* @regs: List of regions to be authenticated
@ -226,46 +288,6 @@ bool efi_signature_verify_with_list(struct efi_image_regions *regs,
EFI_PRINT("%s: Enter, %p, %p, %p, %p\n", __func__,
regs, signed_info, siglist, valid_cert);
if (!signed_info) {
void *hash = NULL;
size_t size;
EFI_PRINT("%s: unsigned image\n", __func__);
/*
* verify based on calculated hash value
* TODO: support other hash algorithms
*/
if (guidcmp(&siglist->sig_type, &efi_guid_sha256)) {
EFI_PRINT("Digest algorithm is not supported: %pUl\n",
&siglist->sig_type);
goto out;
}
if (!efi_hash_regions(regs->reg, regs->num, &hash, &size)) {
EFI_PRINT("Digesting unsigned image failed\n");
goto out;
}
/* go through the list */
for (sig_data = siglist->sig_data_list; sig_data;
sig_data = sig_data->next) {
#ifdef DEBUG
EFI_PRINT("Msg digest in database:\n");
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)) {
verified = true;
free(hash);
goto out;
}
}
free(hash);
goto out;
}
EFI_PRINT("%s: signed image\n", __func__);
if (guidcmp(&siglist->sig_type, &efi_guid_cert_x509)) {
EFI_PRINT("Signature type is not supported: %pUl\n",
&siglist->sig_type);
@ -412,19 +434,6 @@ bool efi_signature_verify_one(struct efi_image_regions *regs,
if (!db->sig_data_list)
goto out;
/* for unsigned image */
if (!msg) {
EFI_PRINT("%s: Verify unsigned image with db\n", __func__);
for (siglist = db; siglist; siglist = siglist->next)
if (efi_signature_verify_with_list(regs, NULL, NULL,
siglist, &cert)) {
verified = true;
break;
}
goto out;
}
/* for signed image or variable */
EFI_PRINT("%s: Verify signed image with db\n", __func__);
for (sinfo = msg->signed_infos; sinfo; sinfo = sinfo->next) {
EFI_PRINT("Signed Info: digest algo: %s, pkey algo: %s\n",
@ -468,26 +477,9 @@ bool efi_signature_verify_with_sigdb(struct efi_image_regions *regs,
EFI_PRINT("%s: Enter, %p, %p, %p, %p\n", __func__, regs, msg, db, dbx);
if (!db)
if (!regs || !msg || !db || !db->sig_data_list)
goto out;
if (!db->sig_data_list)
goto out;
/* for unsigned image */
if (!msg) {
EFI_PRINT("%s: Verify unsigned image with db\n", __func__);
for (siglist = db; siglist; siglist = siglist->next)
if (efi_signature_verify_with_list(regs, NULL, NULL,
siglist, &cert)) {
verified = true;
break;
}
goto out;
}
/* for signed image or variable */
EFI_PRINT("%s: Verify signed image with db\n", __func__);
for (info = msg->signed_infos; info; info = info->next) {
EFI_PRINT("Signed Info: digest algo: %s, pkey algo: %s\n",
info->sig->hash_algo, info->sig->pkey_algo);