Re: [PATCH] SecurityPkg: fix sha256 signature check

[Laszlo Ersek <lersek@redhat.com>]

On 05/10/18 00:09, James Bottomley wrote:
> commit c035e37335ae43229d7e68de74a65f2c01ebc0af
> Author: Zhang Lubo <lubo.zhang@intel.com>
> Date:   Thu Jan 5 14:58:05 2017 +0800
> 
>     SecurityPkg: enhance secure boot Config Dxe & Time Based AuthVariable.
> 
> Added a check for sha256 being the ownly allowed signature hash.
> Unfortuantely this commit assumed the form of the signature data was a
> raw SignedData sequence.  Most tools actually generate a ContentInfo
> sequence instead which contains a header identifying the content as
> pkcs7-SignedData.  Fix this check to allow either format to work.
> 
> This fix is needed at least for efitools because we generate signed
> variable updates with the ContentInfo header.
> 
> Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
> ---
>  CryptoPkg/Library/OpensslLib/openssl              |  2 +-
>  SecurityPkg/Library/AuthVariableLib/AuthService.c | 11 ++++++++++-
>  2 files changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/CryptoPkg/Library/OpensslLib/openssl b/CryptoPkg/Library/OpensslLib/openssl
> index b2758a2292..d4e4bd2a81 160000
> --- a/CryptoPkg/Library/OpensslLib/openssl
> +++ b/CryptoPkg/Library/OpensslLib/openssl
> @@ -1 +1 @@
> -Subproject commit b2758a2292aceda93e9f44c219b94fe21bb9a650
> +Subproject commit d4e4bd2a8163f355fa8a3884077eaec7adc75ff7

This hunk should not be necessary; please see edk2 commit b85b20fba42e
("CryptoPkg/OpensslLib: Update OpenSSL version to 1.1.0h", 2018-04-15).

(I'll let the SecurityPkg maintainers review the rest.)

Thanks,
Laszlo

> diff --git a/SecurityPkg/Library/AuthVariableLib/AuthService.c b/SecurityPkg/Library/AuthVariableLib/AuthService.c
> index 213a524f27..855ea3350a 100644
> --- a/SecurityPkg/Library/AuthVariableLib/AuthService.c
> +++ b/SecurityPkg/Library/AuthVariableLib/AuthService.c
> @@ -1908,10 +1908,19 @@ VerifyTimeBasedPayload (
>    //    in VARIABLE_AUTHENTICATION_2 descriptor.
>    //    This field has the fixed offset (+13) and be calculated based on two bytes of length encoding.
>    //
> +  // However the data may also begin
> +  //   ContentInfo ::= SEQUENCE {
> +  //	   contentType ContentType,
> +  //	   content
> +  //	     [0] EXPLICIT ANY DEFINED BY contentType OPTIONAL }
> +  //
> +  // In which case the fixed offset is +32
> +  //
>    if ((Attributes & EFI_VARIABLE_TIME_BASED_AUTHENTICATED_WRITE_ACCESS) != 0) {
>      if (SigDataSize >= (13 + sizeof (mSha256OidValue))) {
>        if (((*(SigData + 1) & TWO_BYTE_ENCODE) != TWO_BYTE_ENCODE) || 
> -           (CompareMem (SigData + 13, &mSha256OidValue, sizeof (mSha256OidValue)) != 0)) {
> +	  (CompareMem (SigData + 13, &mSha256OidValue, sizeof (mSha256OidValue)) != 0 &&
> +	   CompareMem (SigData + 32, &mSha256OidValue, sizeof (mSha256OidValue)) != 0)) {
>            return EFI_SECURITY_VIOLATION;
>          }
>      }
>