Re: [PATCH 6/9] SecurityPkg/DxeImageVerificationLib: Differentiate error and search result in IsCertHashFoundInDatabase(CVE-2019-14575)

["Wang, Jian J" <jian.j.wang@intel.com>]

Jiewen,

Thanks for the comments.

1) You're right. IsCertHashFoundInDatabase is quite general and cause confusions between
db and dbx situation. Since it's not newly introduced in this patch series, do you think it's ok
to fix it in separate patch series later? Or do you prefer fix it in this patch series? I'm ok with
both.

2) I checked both code again. I think you're right. Both callings are for dbx, any error Status
should be taken as IsFound(==TRUE). What about following change for the second case?
Please help double check if any logic hole here.

            Status = IsCertHashFoundInDatabase (...);
            if (EFI_ERROR (Status) || IsFound) {
              //
              // Check the timestamp signature and signing time to determine if the RootCert can be trusted.
              //
              VerifyStatus = PassTimestampCheck (AuthData, AuthDataSize, &RevocationTime);
              if (!VerifyStatus) {
                DEBUG ((...));
              }
            } else  {
              VerifyStatus = TRUE;
            }

             goto Done;

Regards,
Jian

> -----Original Message-----
> From: Yao, Jiewen <jiewen.yao@intel.com>
> Sent: Thursday, February 13, 2020 6:11 PM
> To: Wang, Jian J <jian.j.wang@intel.com>; devel@edk2.groups.io
> Cc: Zhang, Chao B <chao.b.zhang@intel.com>; Laszlo Ersek
> <lersek@redhat.com>
> Subject: RE: [PATCH 6/9] SecurityPkg/DxeImageVerificationLib: Differentiate
> error and search result in IsCertHashFoundInDatabase(CVE-2019-14575)
> 
> 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@intel.com>
> > Sent: Thursday, February 6, 2020 10:20 PM
> > To: devel@edk2.groups.io
> > Cc: Yao, Jiewen <jiewen.yao@intel.com>; Zhang, Chao B
> > <chao.b.zhang@intel.com>; Laszlo Ersek <lersek@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@intel.com>
> > Cc: Chao Zhang <chao.b.zhang@intel.com>
> > Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
> > Signed-off-by: Laszlo Ersek <lersek@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