Re: [edk2-devel] [PATCH v7 11/14] SecurityPkg: Allow VariablePolicy state to delete authenticated variables

["Yao, Jiewen" <jiewen.yao@intel.com>]

Hi Bret
I have minor comment below. Please let me know your thought.

 
> -----邮件原件-----
> 发件人: bounce+27952+64723+4905953+8761045@groups.io
> <bounce+27952+64723+4905953+8761045@groups.io> 代表 Bret Barkelew
> 发送时间: 2020年8月28日 13:51
> 收件人: devel@edk2.groups.io
> 抄送: Jiewen Yao <jiewen.yao@intel.com>; Jian J Wang
> <jian.j.wang@intel.com>; Chao Zhang <chao.b.zhang@intel.com>
> 主题: [edk2-devel] [PATCH v7 11/14] SecurityPkg: Allow VariablePolicy state
> to delete authenticated variables
> 
> https://bugzilla.tianocore.org/show_bug.cgi?id=2522
> 
> Causes AuthService to check
> IsVariablePolicyEnabled() before enforcing
> write protections to allow variable deletion
> when policy engine is disabled.
> 
> Only allows deletion, not modification.
> 
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Cc: Jian J Wang <jian.j.wang@intel.com>
> Cc: Chao Zhang <chao.b.zhang@intel.com>
> Cc: Bret Barkelew <brbarkel@microsoft.com>
> Signed-off-by: Bret Barkelew <brbarkel@microsoft.com>
> ---
>  SecurityPkg/Library/AuthVariableLib/AuthService.c       | 22
> ++++++++++++++++----
>  SecurityPkg/Library/AuthVariableLib/AuthVariableLib.inf |  2 ++
>  2 files changed, 20 insertions(+), 4 deletions(-)
> 
> diff --git a/SecurityPkg/Library/AuthVariableLib/AuthService.c
> b/SecurityPkg/Library/AuthVariableLib/AuthService.c
> index 2f60331f2c04..aca9a5620c28 100644
> --- a/SecurityPkg/Library/AuthVariableLib/AuthService.c
> +++ b/SecurityPkg/Library/AuthVariableLib/AuthService.c
> @@ -19,12 +19,16 @@
>    to verify the signature.
> 
> 
> 
>  Copyright (c) 2009 - 2019, Intel Corporation. All rights reserved.<BR>
> 
> +Copyright (c) Microsoft Corporation.
> 
>  SPDX-License-Identifier: BSD-2-Clause-Patent
> 
> 
> 
>  **/
> 
> 
> 
>  #include "AuthServiceInternal.h"
> 
> 
> 
> +#include <Protocol/VariablePolicy.h>
> 
> +#include <Library/VariablePolicyLib.h>
> 
> +
> 
>  //
> 
>  // Public Exponent of RSA Key.
> 
>  //
> 
> @@ -217,9 +221,12 @@ NeedPhysicallyPresent(
>    IN     EFI_GUID       *VendorGuid
> 
>    )
> 
>  {
> 
> -  if ((CompareGuid (VendorGuid, &gEfiSecureBootEnableDisableGuid) &&
> (StrCmp (VariableName, EFI_SECURE_BOOT_ENABLE_NAME) == 0))
> 
> -    || (CompareGuid (VendorGuid, &gEfiCustomModeEnableGuid) && (StrCmp
> (VariableName, EFI_CUSTOM_MODE_NAME) == 0))) {
> 
> -    return TRUE;
> 
> +  // If the VariablePolicy engine is disabled, allow deletion of any
> authenticated variables.
> 
> +  if (IsVariablePolicyEnabled()) {
> 
> +    if ((CompareGuid (VendorGuid, &gEfiSecureBootEnableDisableGuid) &&
> (StrCmp (VariableName, EFI_SECURE_BOOT_ENABLE_NAME) == 0))
> 
> +      || (CompareGuid (VendorGuid, &gEfiCustomModeEnableGuid) && (StrCmp
> (VariableName, EFI_CUSTOM_MODE_NAME) == 0))) {
> 
> +      return TRUE;
> 
> +    }
> 
>    }

[Jiewen] Looks good.

> 
> 
>    return FALSE;
> 
> @@ -842,7 +849,8 @@ ProcessVariable (
>               &OrgVariableInfo
> 
>               );
> 
> 
> 
> -  if ((!EFI_ERROR (Status)) && IsDeleteAuthVariable
> (OrgVariableInfo.Attributes, Data, DataSize, Attributes) &&
> UserPhysicalPresent()) {
> 
> +  // If the VariablePolicy engine is disabled, allow deletion of any
> authenticated variables.
> 
> +  if ((!EFI_ERROR (Status)) && IsDeleteAuthVariable
> (OrgVariableInfo.Attributes, Data, DataSize, Attributes) &&
> (UserPhysicalPresent() || !IsVariablePolicyEnabled())) {
> 

[Jiewen] Looks good.

>      //
> 
>      // Allow the delete operation of common authenticated variable(AT or
> AW) at user physical presence.
> 
>      //
> 
> @@ -1960,6 +1968,12 @@ VerifyTimeBasedPayload (
> 
> 
>    CopyMem (Buffer, PayloadPtr, PayloadSize);
> 
> 
> 
> +  // If the VariablePolicy engine is disabled, allow deletion of any
> authenticated variables.
> 
> +  if (PayloadSize == 0 && (Attributes & EFI_VARIABLE_APPEND_WRITE) == 0 &&
> !IsVariablePolicyEnabled()) {
> 
> +    VerifyStatus = TRUE;
> 
> +    goto Exit;
> 
> +  }
> 

[Jiewen] I checked the programming context. 
If we are going to skip the check, I feel the GetScratchBuffer() and CopyMem () may be avoided.
Also, I do not find any those data are used at Exit.

How about we move the check just after getting PayloadSize?
  //
  // Find out the new data payload which follows Pkcs7 SignedData directly.
  //
  PayloadPtr = SigData + SigDataSize;
  PayloadSize = DataSize - OFFSET_OF_AUTHINFO2_CERT_DATA - (UINTN) SigDataSize;
I hope it can make logic clearer.


One more thing is about below action at Exit.
Pkcs7FreeSigners (TopLevelCert);
Pkcs7FreeSigners (SignerCerts);

With new short path, we can come here with NULL point for Pkcs7FreeSigners().
I don't know the result if we pass a NULL pointer according to Pkcs7FreeSigners() API definition.
/**
  Wrap function to use free() to free allocated memory for certificates.
  If this interface is not supported, then ASSERT().
  @param[in]  Certs        Pointer to the certificates to be freed.
**/
VOID
EFIAPI
Pkcs7FreeSigners (
  IN  UINT8        *Certs
  );

I notice the current openssl version BaseCryptoLib implementation will check NULL and return.
We are safe in the default one. But I am not sure about other implementation.

I recommend we either document NULL pointer behavior in Pkcs7FreeSigners(), or add NULL pointer check at Exit to avoid calling Pkcs7FreeSigners().

With above two update, reviewed-by: Jiewen Yao <Jiewen.yao@intel.com>


> +
> 
>    if (AuthVarType == AuthVarTypePk) {
> 
>      //
> 
>      // Verify that the signature has been made with the current Platform
> Key (no chaining for PK).
> 
> diff --git a/SecurityPkg/Library/AuthVariableLib/AuthVariableLib.inf
> b/SecurityPkg/Library/AuthVariableLib/AuthVariableLib.inf
> index 8d4ce14df494..8eadeebcebd7 100644
> --- a/SecurityPkg/Library/AuthVariableLib/AuthVariableLib.inf
> +++ b/SecurityPkg/Library/AuthVariableLib/AuthVariableLib.inf
> @@ -3,6 +3,7 @@
>  #
> 
>  #  Copyright (c) 2015 - 2016, Intel Corporation. All rights reserved.<BR>
> 
>  #  Copyright (c) 2018, ARM Limited. All rights reserved.<BR>
> 
> +#  Copyright (c) Microsoft Corporation.
> 
>  #
> 
>  #  SPDX-License-Identifier: BSD-2-Clause-Patent
> 
>  #
> 
> @@ -41,6 +42,7 @@ [LibraryClasses]
>    MemoryAllocationLib
> 
>    BaseCryptLib
> 
>    PlatformSecureLib
> 
> +  VariablePolicyLib
> 
> 
> 
>  [Guids]
> 
>    ## CONSUMES            ## Variable:L"SetupMode"
> 
> --
> 2.28.0.windows.1
> 
> 
> -=-=-=-=-=-=
> Groups.io Links: You receive all messages sent to this group.
> 
> View/Reply Online (#64723): https://edk2.groups.io/g/devel/message/64723
> Mute This Topic: https://groups.io/mt/76468137/4905953
> Group Owner: devel+owner@edk2.groups.io
> Unsubscribe: https://edk2.groups.io/g/devel/unsub
> [gaoliming@byosoft.com.cn]
> -=-=-=-=-=-=
> 
>