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efi_loader: signature: correct a behavior against multiple signatures

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Under the current implementation, all the signatures, if any, in
a signed image must be verified before loading it.

Meanwhile, UEFI specification v2.8b section 32.5.3.3 says,
    Multiple signatures are allowed to exist in the binary’s certificate
    table (as per PE/COFF Section “Attribute Certificate Table”). Only
    one hash or signature is required to be present in db in order to pass
    validation, so long as neither the SHA-256 hash of the binary nor any
    present signature is reflected in dbx.

This patch makes the semantics of signature verification compliant with
the specification mentioned above.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Reported-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
This commit is contained in:
AKASHI Takahiro 2020-08-14 14:39:23 +09:00 committed by Heinrich Schuchardt
parent f68a6d5835
commit 52956e535e
3 changed files with 30 additions and 88 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

9
include/efi_loader.h
View file

@ -773,13 +773,16 @@ 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);
bool efi_signature_verify(struct efi_image_regions *regs,
struct pkcs7_message *msg,
struct efi_signature_store *db,
struct efi_signature_store *dbx);
static inline bool efi_signature_verify_one(struct efi_image_regions *regs,
struct pkcs7_message *msg,
struct efi_signature_store *db)
{
return efi_signature_verify(regs, msg, db, NULL);
}
bool efi_signature_check_signers(struct pkcs7_message *msg,
struct efi_signature_store *dbx);

33
lib/efi_loader/efi_image_loader.c
View file

@ -546,6 +546,11 @@ static bool efi_image_authenticate(void *efi, size_t efi_size)
goto err;
}
if (efi_signature_lookup_digest(regs, dbx)) {
EFI_PRINT("Image's digest was found in \"dbx\"\n");
goto err;
}
/*
* go through WIN_CERTIFICATE list
* NOTE:
@ -553,10 +558,9 @@ static bool efi_image_authenticate(void *efi, size_t efi_size)
* in PE header, or as pkcs7 SignerInfo's in SignedData.
* So the verification policy here is:
* - Success if, at least, one of signatures is verified
* - unless
* any of signatures is rejected explicitly, or
* none of digest algorithms are supported
* - unless signature is rejected explicitly with its digest.
*/
for (wincert = wincerts, wincerts_end = (u8 *)wincerts + wincerts_len;
(u8 *)wincert < wincerts_end;
wincert = (WIN_CERTIFICATE *)
@ -627,32 +631,29 @@ static bool efi_image_authenticate(void *efi, size_t efi_size)
/* try black-list first */
if (efi_signature_verify_one(regs, msg, dbx)) {
EFI_PRINT("Signature was rejected by \"dbx\"\n");
goto err;
continue;
}
if (!efi_signature_check_signers(msg, dbx)) {
EFI_PRINT("Signer(s) in \"dbx\"\n");
goto err;
}
if (efi_signature_lookup_digest(regs, dbx)) {
EFI_PRINT("Image's digest was found in \"dbx\"\n");
goto err;
continue;
}
/* try white-list */
if (efi_signature_verify(regs, msg, db, dbx))
continue;
if (efi_signature_verify(regs, msg, db, dbx)) {
ret = true;
break;
}
debug("Signature was not verified by \"db\"\n");
if (efi_signature_lookup_digest(regs, db))
continue;
if (efi_signature_lookup_digest(regs, db)) {
ret = true;
break;
}
debug("Image's digest was not found in \"db\" or \"dbx\"\n");
goto err;
}
ret = true;
err:
efi_sigstore_free(db);

76
lib/efi_loader/efi_signature.c
View file

@ -174,6 +174,8 @@ static bool efi_lookup_certificate(struct x509_certificate *cert,
if (IS_ERR_OR_NULL(cert_tmp))
continue;
EFI_PRINT("%s: against %s\n", __func__,
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))
@ -266,7 +268,7 @@ out:
* protocol at this time and any image will be unconditionally revoked
* when this match occurs.
*
* Return: true if check passed, false otherwise.
* Return: true if check passed (not found), false otherwise.
*/
static bool efi_signature_check_revocation(struct pkcs7_signed_info *sinfo,
struct x509_certificate *cert,
@ -336,70 +338,6 @@ out:
return !revoked;
}
/**
* efi_signature_verify_one - verify signatures with database
* @regs: List of regions to be authenticated
* @msg: Signature
* @db: Signature database
*
* All the signature pointed to by @msg against image pointed to by @regs
* will be verified by signature database pointed to by @db.
*
* Return: true if verification for one of signatures passed, false
* otherwise
*/
bool efi_signature_verify_one(struct efi_image_regions *regs,
struct pkcs7_message *msg,
struct efi_signature_store *db)
{
struct pkcs7_signed_info *sinfo;
struct x509_certificate *signer;
bool verified = false;
int ret;
EFI_PRINT("%s: Enter, %p, %p, %p\n", __func__, regs, msg, db);
if (!db)
goto out;
if (!db->sig_data_list)
goto out;
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",
sinfo->sig->hash_algo, sinfo->sig->pkey_algo);
EFI_PRINT("Verifying certificate chain\n");
signer = NULL;
ret = pkcs7_verify_one(msg, sinfo, &signer);
if (ret == -ENOPKG)
continue;
if (ret < 0 || !signer)
goto out;
if (sinfo->blacklisted)
continue;
EFI_PRINT("Verifying last certificate in chain\n");
if (signer->self_signed) {
if (efi_lookup_certificate(signer, db)) {
verified = true;
goto out;
}
} else if (efi_verify_certificate(signer, db, NULL)) {
verified = true;
goto out;
}
EFI_PRINT("Valid certificate not in db\n");
}
out:
EFI_PRINT("%s: Exit, verified: %d\n", __func__, verified);
return verified;
}
/*
* efi_signature_verify - verify signatures with db and dbx
* @regs: List of regions to be authenticated
@ -462,7 +400,7 @@ bool efi_signature_verify(struct efi_image_regions *regs,
if (efi_lookup_certificate(signer, db))
if (efi_signature_check_revocation(sinfo,
signer, dbx))
continue;
break;
} else if (efi_verify_certificate(signer, db, &root)) {
bool check;
@ -470,13 +408,13 @@ bool efi_signature_verify(struct efi_image_regions *regs,
dbx);
x509_free_certificate(root);
if (check)
continue;
break;
}
EFI_PRINT("Certificate chain didn't reach trusted CA\n");
goto out;
}
verified = true;
if (sinfo)
verified = true;
out:
EFI_PRINT("%s: Exit, verified: %d\n", __func__, verified);
return verified;