From adc6898366298d1f64b91785e50095527f682758 Mon Sep 17 00:00:00 2001 From: Jian J Wang Date: Thu, 10 Oct 2019 15:49:55 +0800 Subject: [PATCH] SecurityPkg/DxeImageVerificationLib: refactor db/dbx fetching code (CVE-2019-14575) REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1608 The dbx fetching code inside the while/for-loop causes code hard to understand. Since there's no need to get dbx more than once, this patch simplify the code logic by moving related code to be outside the while- loop. db fetching code is also refined accordingly to reduce the indent level of code. More comments are also added or refined to explain more details. Cc: Jiewen Yao Cc: Chao Zhang Signed-off-by: Jian J Wang Reviewed-by: Jiewen Yao --- .../DxeImageVerificationLib.c | 144 ++++++++++-------- 1 file changed, 83 insertions(+), 61 deletions(-) diff --git a/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c b/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c index ed5dbf26b0..8739d1fa29 100644 --- a/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c +++ b/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c @@ -1412,76 +1412,92 @@ IsAllowedByDb ( RootCertSize = 0; VerifyStatus = FALSE; + // + // Fetch 'db' content. If 'db' doesn't exist or encounters problem to get the + // data, return not-allowed-by-db (FALSE). + // DataSize = 0; Status = gRT->GetVariable (EFI_IMAGE_SECURITY_DATABASE, &gEfiImageSecurityDatabaseGuid, NULL, &DataSize, NULL); - if (Status == EFI_BUFFER_TOO_SMALL) { - Data = (UINT8 *) AllocateZeroPool (DataSize); - if (Data == NULL) { - return VerifyStatus; + ASSERT (EFI_ERROR (Status)); + if (Status != EFI_BUFFER_TOO_SMALL) { + return VerifyStatus; + } + + Data = (UINT8 *) AllocateZeroPool (DataSize); + if (Data == NULL) { + return VerifyStatus; + } + + Status = gRT->GetVariable (EFI_IMAGE_SECURITY_DATABASE, &gEfiImageSecurityDatabaseGuid, NULL, &DataSize, (VOID *) Data); + if (EFI_ERROR (Status)) { + goto Done; + } + + // + // Fetch 'dbx' content. If 'dbx' doesn't exist, continue to check 'db'. + // If any other errors occured, no need to check 'db' but just return + // not-allowed-by-db (FALSE) to avoid bypass. + // + DbxDataSize = 0; + Status = gRT->GetVariable (EFI_IMAGE_SECURITY_DATABASE1, &gEfiImageSecurityDatabaseGuid, NULL, &DbxDataSize, NULL); + ASSERT (EFI_ERROR (Status)); + if (Status != EFI_BUFFER_TOO_SMALL) { + if (Status != EFI_NOT_FOUND) { + goto Done; + } + // + // 'dbx' does not exist. Continue to check 'db'. + // + } else { + // + // 'dbx' exists. Get its content. + // + DbxData = (UINT8 *) AllocateZeroPool (DbxDataSize); + if (DbxData == NULL) { + goto Done; } - Status = gRT->GetVariable (EFI_IMAGE_SECURITY_DATABASE, &gEfiImageSecurityDatabaseGuid, NULL, &DataSize, (VOID *) Data); + Status = gRT->GetVariable (EFI_IMAGE_SECURITY_DATABASE1, &gEfiImageSecurityDatabaseGuid, NULL, &DbxDataSize, (VOID *) DbxData); if (EFI_ERROR (Status)) { goto Done; } + } - // - // Find X509 certificate in Signature List to verify the signature in pkcs7 signed data. - // - CertList = (EFI_SIGNATURE_LIST *) Data; - while ((DataSize > 0) && (DataSize >= CertList->SignatureListSize)) { - if (CompareGuid (&CertList->SignatureType, &gEfiCertX509Guid)) { - CertData = (EFI_SIGNATURE_DATA *) ((UINT8 *) CertList + sizeof (EFI_SIGNATURE_LIST) + CertList->SignatureHeaderSize); - CertCount = (CertList->SignatureListSize - sizeof (EFI_SIGNATURE_LIST) - CertList->SignatureHeaderSize) / CertList->SignatureSize; + // + // Find X509 certificate in Signature List to verify the signature in pkcs7 signed data. + // + CertList = (EFI_SIGNATURE_LIST *) Data; + while ((DataSize > 0) && (DataSize >= CertList->SignatureListSize)) { + if (CompareGuid (&CertList->SignatureType, &gEfiCertX509Guid)) { + CertData = (EFI_SIGNATURE_DATA *) ((UINT8 *) CertList + sizeof (EFI_SIGNATURE_LIST) + CertList->SignatureHeaderSize); + CertCount = (CertList->SignatureListSize - sizeof (EFI_SIGNATURE_LIST) - CertList->SignatureHeaderSize) / CertList->SignatureSize; - for (Index = 0; Index < CertCount; Index++) { - // - // Iterate each Signature Data Node within this CertList for verify. - // - RootCert = CertData->SignatureData; - RootCertSize = CertList->SignatureSize - sizeof (EFI_GUID); + for (Index = 0; Index < CertCount; Index++) { + // + // Iterate each Signature Data Node within this CertList for verify. + // + RootCert = CertData->SignatureData; + RootCertSize = CertList->SignatureSize - sizeof (EFI_GUID); + // + // Call AuthenticodeVerify library to Verify Authenticode struct. + // + VerifyStatus = AuthenticodeVerify ( + AuthData, + AuthDataSize, + RootCert, + RootCertSize, + mImageDigest, + mImageDigestSize + ); + if (VerifyStatus) { // - // Call AuthenticodeVerify library to Verify Authenticode struct. + // The image is signed and its signature is found in 'db'. // - VerifyStatus = AuthenticodeVerify ( - AuthData, - AuthDataSize, - RootCert, - RootCertSize, - mImageDigest, - mImageDigestSize - ); - if (VerifyStatus) { + if (DbxData != NULL) { // // Here We still need to check if this RootCert's Hash is revoked // - DbxDataSize = 0; - Status = gRT->GetVariable (EFI_IMAGE_SECURITY_DATABASE1, &gEfiImageSecurityDatabaseGuid, NULL, &DbxDataSize, NULL); - if (Status != EFI_BUFFER_TOO_SMALL) { - if (Status != EFI_NOT_FOUND) { - VerifyStatus = FALSE; - } - goto Done; - } - DbxData = (UINT8 *) AllocateZeroPool (DbxDataSize); - if (DbxData == NULL) { - // - // Force not-allowed-by-db to avoid bypass - // - VerifyStatus = FALSE; - goto Done; - } - - Status = gRT->GetVariable (EFI_IMAGE_SECURITY_DATABASE1, &gEfiImageSecurityDatabaseGuid, NULL, &DbxDataSize, (VOID *) DbxData); - if (EFI_ERROR (Status)) { - // - // Force not-allowed-by-db to avoid bypass - // - VerifyStatus = FALSE; - goto Done; - } - 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. @@ -1491,17 +1507,23 @@ IsAllowedByDb ( DEBUG ((DEBUG_INFO, "DxeImageVerificationLib: Image is signed and signature is accepted by DB, but its root cert failed the timestamp check.\n")); } } - - goto Done; } - CertData = (EFI_SIGNATURE_DATA *) ((UINT8 *) CertData + CertList->SignatureSize); + // + // There's no 'dbx' to check revocation time against (must-be pass), + // or, there's revocation time found in 'dbx' and checked againt 'dbt' + // (maybe pass or fail, depending on timestamp compare result). Either + // way the verification job has been completed at this point. + // + goto Done; } - } - DataSize -= CertList->SignatureListSize; - CertList = (EFI_SIGNATURE_LIST *) ((UINT8 *) CertList + CertList->SignatureListSize); + CertData = (EFI_SIGNATURE_DATA *) ((UINT8 *) CertData + CertList->SignatureSize); + } } + + DataSize -= CertList->SignatureListSize; + CertList = (EFI_SIGNATURE_LIST *) ((UINT8 *) CertList + CertList->SignatureListSize); } Done: -- 2.39.2