[edk2-devel] [PATCH 6/9] SecurityPkg/DxeImageVerificationLib: Differentiate error and search result in IsCertHashFoundInDatabase(CVE-2019-14575)
Yao, Jiewen
jiewen.yao at intel.com
Thu Feb 13 10:11:11 UTC 2020
Comment below:
1) I think the function name - IsCertHashFoundInDatabase() and the implementation { DbxList = SignatureList; DbxSize = SignatureListSize; } bring some confusion to me.
If this is a *generic* database search function, I recommend we use a generic name - not use DbxList/DbxSize in the function implementation.
If the input SignatureList of the function must be *Dbx*, I recommend we use IsCertHashFoundInDbx() as the function name.
Either change is OK for me.
2) Now we have to check 2 output: Status and IsFound in IsCertHashFoundInDatabase().
I am struggling to understand the different between 2 different ways of error handling:
===========================
Status = IsCertHashFoundInDatabase (Cert, CertSize, (EFI_SIGNATURE_LIST *)Data, DataSize, &RevocationTime, &IsFound);
if (EFI_ERROR (Status) || IsFound) {
//
// Check the timestamp signature and signing time to determine if the image can be trusted.
//
IsForbidden = TRUE;
if (!EFI_ERROR (Status) && PassTimestampCheck (AuthData, AuthDataSize, &RevocationTime)) {
IsForbidden = FALSE;
============================
and
============================
VerifyStatus = FALSE;
//
// Here We still need to check if this RootCert's Hash is revoked
//
Status = IsCertHashFoundInDatabase (RootCert, RootCertSize, (EFI_SIGNATURE_LIST *)DbxData, DbxDataSize, &RevocationTime, &IsFound);
if (EFI_ERROR (Status)) {
goto Done;
}
if (!IsFound) {
VerifyStatus = TRUE;
goto Done;
}
//
// Check the timestamp signature and signing time to determine if the RootCert can be trusted.
//
VerifyStatus = PassTimestampCheck (AuthData, AuthDataSize, &RevocationTime);
if (!VerifyStatus) {
===============================
I *believe* the logic behind is same. If so, we can use a consistent way to check the 2 output and decide if PassTimestampCheck() is required.
Or, can we create a one single function to perform such check for both IsCertHashFoundInDatabase() and PassTimestampCheck() ?
If I am wrong, there is *difference* between them. Then I think we need much better description to help reviewer to catch the difference.
Thank you
Yao Jiewen
> -----Original Message-----
> From: Wang, Jian J <jian.j.wang at intel.com>
> Sent: Thursday, February 6, 2020 10:20 PM
> To: devel at edk2.groups.io
> Cc: Yao, Jiewen <jiewen.yao at intel.com>; Zhang, Chao B
> <chao.b.zhang at intel.com>; Laszlo Ersek <lersek at redhat.com>
> Subject: [PATCH 6/9] SecurityPkg/DxeImageVerificationLib: Differentiate error
> and search result in IsCertHashFoundInDatabase(CVE-2019-14575)
>
> REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1608
>
> To avoid false-negative issue in check hash against dbx, both error
> condition (as return value) and check result (as out parameter) of
> IsCertHashFoundInDatabase() are added. So the caller of this function
> will know exactly if a failure is caused by a black list hit or
> other error happening, and enforce a more secure operation to prevent
> secure boot from being bypassed. For a white list check (db), there's
> no such necessity.
>
> Cc: Jiewen Yao <jiewen.yao at intel.com>
> Cc: Chao Zhang <chao.b.zhang at intel.com>
> Signed-off-by: Jian J Wang <jian.j.wang at intel.com>
> Signed-off-by: Laszlo Ersek <lersek at redhat.com>
> ---
> .../DxeImageVerificationLib.c | 68 +++++++++++--------
> 1 file changed, 41 insertions(+), 27 deletions(-)
>
> diff --git
> a/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c
> b/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c
> index 8739d1fa29..a5dfee0f8e 100644
> --- a/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c
> +++ b/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c
> @@ -822,22 +822,23 @@ AddImageExeInfo (
> @param[in] SignatureList Pointer to the Signature List in forbidden database.
>
> @param[in] SignatureListSize Size of Signature List.
>
> @param[out] RevocationTime Return the time that the certificate was
> revoked.
>
> + @param[out] IsFound Search result. Only valid if EFI_SUCCESS returned.
>
>
>
> - @return TRUE The certificate hash is found in the forbidden database.
>
> - @return FALSE The certificate hash is not found in the forbidden database.
>
> + @retval EFI_SUCCESS Finished the search without any error.
>
> + @retval Others Error occurred in the search of database.
>
>
>
> **/
>
> -BOOLEAN
>
> +EFI_STATUS
>
> IsCertHashFoundInDatabase (
>
> IN UINT8 *Certificate,
>
> IN UINTN CertSize,
>
> IN EFI_SIGNATURE_LIST *SignatureList,
>
> IN UINTN SignatureListSize,
>
> - OUT EFI_TIME *RevocationTime
>
> + OUT EFI_TIME *RevocationTime,
>
> + OUT BOOLEAN *IsFound
>
> )
>
> {
>
> - BOOLEAN IsFound;
>
> - BOOLEAN Status;
>
> + EFI_STATUS Status;
>
> EFI_SIGNATURE_LIST *DbxList;
>
> UINTN DbxSize;
>
> EFI_SIGNATURE_DATA *CertHash;
>
> @@ -851,21 +852,22 @@ IsCertHashFoundInDatabase (
> UINT8 *TBSCert;
>
> UINTN TBSCertSize;
>
>
>
> - IsFound = FALSE;
>
> + Status = EFI_ABORTED;
>
> + *IsFound = FALSE;
>
> DbxList = SignatureList;
>
> DbxSize = SignatureListSize;
>
> HashCtx = NULL;
>
> HashAlg = HASHALG_MAX;
>
>
>
> if ((RevocationTime == NULL) || (DbxList == NULL)) {
>
> - return FALSE;
>
> + return EFI_INVALID_PARAMETER;
>
> }
>
>
>
> //
>
> // Retrieve the TBSCertificate from the X.509 Certificate.
>
> //
>
> if (!X509GetTBSCert (Certificate, CertSize, &TBSCert, &TBSCertSize)) {
>
> - return FALSE;
>
> + return Status;
>
> }
>
>
>
> while ((DbxSize > 0) && (SignatureListSize >= DbxList->SignatureListSize)) {
>
> @@ -895,16 +897,13 @@ IsCertHashFoundInDatabase (
> if (HashCtx == NULL) {
>
> goto Done;
>
> }
>
> - Status = mHash[HashAlg].HashInit (HashCtx);
>
> - if (!Status) {
>
> + if (!mHash[HashAlg].HashInit (HashCtx)) {
>
> goto Done;
>
> }
>
> - Status = mHash[HashAlg].HashUpdate (HashCtx, TBSCert, TBSCertSize);
>
> - if (!Status) {
>
> + if (!mHash[HashAlg].HashUpdate (HashCtx, TBSCert, TBSCertSize)) {
>
> goto Done;
>
> }
>
> - Status = mHash[HashAlg].HashFinal (HashCtx, CertDigest);
>
> - if (!Status) {
>
> + if (!mHash[HashAlg].HashFinal (HashCtx, CertDigest)) {
>
> goto Done;
>
> }
>
>
>
> @@ -923,7 +922,8 @@ IsCertHashFoundInDatabase (
> //
>
> // Hash of Certificate is found in forbidden database.
>
> //
>
> - IsFound = TRUE;
>
> + Status = EFI_SUCCESS;
>
> + *IsFound = TRUE;
>
>
>
> //
>
> // Return the revocation time.
>
> @@ -938,12 +938,14 @@ IsCertHashFoundInDatabase (
> DbxList = (EFI_SIGNATURE_LIST *) ((UINT8 *) DbxList + DbxList-
> >SignatureListSize);
>
> }
>
>
>
> + Status = EFI_SUCCESS;
>
> +
>
> Done:
>
> if (HashCtx != NULL) {
>
> FreePool (HashCtx);
>
> }
>
>
>
> - return IsFound;
>
> + return Status;
>
> }
>
>
>
> /**
>
> @@ -1216,6 +1218,7 @@ IsForbiddenByDbx (
> {
>
> EFI_STATUS Status;
>
> BOOLEAN IsForbidden;
>
> + BOOLEAN IsFound;
>
> UINT8 *Data;
>
> UINTN DataSize;
>
> EFI_SIGNATURE_LIST *CertList;
>
> @@ -1344,12 +1347,13 @@ IsForbiddenByDbx (
> //
>
> CertPtr = CertPtr + sizeof (UINT32) + CertSize;
>
>
>
> - if (IsCertHashFoundInDatabase (Cert, CertSize, (EFI_SIGNATURE_LIST *)Data,
> DataSize, &RevocationTime)) {
>
> + Status = IsCertHashFoundInDatabase (Cert, CertSize, (EFI_SIGNATURE_LIST
> *)Data, DataSize, &RevocationTime, &IsFound);
>
> + if (EFI_ERROR (Status) || IsFound) {
>
> //
>
> // Check the timestamp signature and signing time to determine if the image
> can be trusted.
>
> //
>
> IsForbidden = TRUE;
>
> - if (PassTimestampCheck (AuthData, AuthDataSize, &RevocationTime)) {
>
> + if (!EFI_ERROR (Status) && PassTimestampCheck (AuthData, AuthDataSize,
> &RevocationTime)) {
>
> IsForbidden = FALSE;
>
> //
>
> // Pass DBT check. Continue to check other certs in image signer's cert list
> against DBX, DBT
>
> @@ -1392,6 +1396,7 @@ IsAllowedByDb (
> {
>
> EFI_STATUS Status;
>
> BOOLEAN VerifyStatus;
>
> + BOOLEAN IsFound;
>
> EFI_SIGNATURE_LIST *CertList;
>
> EFI_SIGNATURE_DATA *CertData;
>
> UINTN DataSize;
>
> @@ -1495,17 +1500,26 @@ IsAllowedByDb (
> // The image is signed and its signature is found in 'db'.
>
> //
>
> if (DbxData != NULL) {
>
> + VerifyStatus = FALSE;
>
> //
>
> // Here We still need to check if this RootCert's Hash is revoked
>
> //
>
> - if (IsCertHashFoundInDatabase (RootCert, RootCertSize,
> (EFI_SIGNATURE_LIST *)DbxData, DbxDataSize, &RevocationTime)) {
>
> - //
>
> - // Check the timestamp signature and signing time to determine if the
> RootCert can be trusted.
>
> - //
>
> - VerifyStatus = PassTimestampCheck (AuthData, AuthDataSize,
> &RevocationTime);
>
> - if (!VerifyStatus) {
>
> - DEBUG ((DEBUG_INFO, "DxeImageVerificationLib: Image is signed and
> signature is accepted by DB, but its root cert failed the timestamp check.\n"));
>
> - }
>
> + Status = IsCertHashFoundInDatabase (RootCert, RootCertSize,
> (EFI_SIGNATURE_LIST *)DbxData, DbxDataSize, &RevocationTime, &IsFound);
>
> + if (EFI_ERROR (Status)) {
>
> + goto Done;
>
> + }
>
> +
>
> + if (!IsFound) {
>
> + VerifyStatus = TRUE;
>
> + goto Done;
>
> + }
>
> +
>
> + //
>
> + // Check the timestamp signature and signing time to determine if the
> RootCert can be trusted.
>
> + //
>
> + VerifyStatus = PassTimestampCheck (AuthData, AuthDataSize,
> &RevocationTime);
>
> + if (!VerifyStatus) {
>
> + DEBUG ((DEBUG_INFO, "DxeImageVerificationLib: Image is signed and
> signature is accepted by DB, but its root cert failed the timestamp check.\n"));
>
> }
>
> }
>
>
>
> --
> 2.24.0.windows.2
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