From a83dbf008cc73406cbdc0d5ac3164cc19fff6683 Mon Sep 17 00:00:00 2001 From: Jian J Wang Date: Mon, 16 Sep 2019 16:52:58 +0800 Subject: [PATCH] SecurityPkg/DxeImageVerificationLib: Differentiate error/search result (1) (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 Cc: Chao Zhang Signed-off-by: Jian J Wang Signed-off-by: Laszlo Ersek Reviewed-by: Jiewen Yao --- .../DxeImageVerificationLib.c | 64 ++++++++++++------- 1 file changed, 42 insertions(+), 22 deletions(-) diff --git a/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c b/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c index 8739d1fa29..85261ba7f2 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 @param[out] RevocationTime Return the time that the certificate was revoked.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; @@ -1344,20 +1347,29 @@ 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)) { // - // Check the timestamp signature and signing time to determine if the image can be trusted. + // Error in searching dbx. Consider it as 'found'. RevocationTime might + // not be valid in such situation. // IsForbidden = TRUE; + } else if (IsFound) { + // + // Found Cert in dbx successfully. Check the timestamp signature and + // signing time to determine if the image can be trusted. + // if (PassTimestampCheck (AuthData, AuthDataSize, &RevocationTime)) { IsForbidden = FALSE; // // Pass DBT check. Continue to check other certs in image signer's cert list against DBX, DBT // continue; + } else { + IsForbidden = TRUE; + DEBUG ((DEBUG_INFO, "DxeImageVerificationLib: Image is signed but signature failed the timestamp check.\n")); + goto Done; } - DEBUG ((DEBUG_INFO, "DxeImageVerificationLib: Image is signed but signature failed the timestamp check.\n")); - goto Done; } } @@ -1392,6 +1404,7 @@ IsAllowedByDb ( { EFI_STATUS Status; BOOLEAN VerifyStatus; + BOOLEAN IsFound; EFI_SIGNATURE_LIST *CertList; EFI_SIGNATURE_DATA *CertData; UINTN DataSize; @@ -1498,7 +1511,14 @@ IsAllowedByDb ( // // Here We still need to check if this RootCert's Hash is revoked // - if (IsCertHashFoundInDatabase (RootCert, RootCertSize, (EFI_SIGNATURE_LIST *)DbxData, DbxDataSize, &RevocationTime)) { + Status = IsCertHashFoundInDatabase (RootCert, RootCertSize, (EFI_SIGNATURE_LIST *)DbxData, DbxDataSize, &RevocationTime, &IsFound); + if (EFI_ERROR (Status)) { + // + // Error in searching dbx. Consider it as 'found'. RevocationTime might + // not be valid in such situation. + // + VerifyStatus = FALSE; + } else if (IsFound) { // // Check the timestamp signature and signing time to determine if the RootCert can be trusted. // -- 2.39.2