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

["Bret Barkelew" <bret.barkelew@microsoft.com>]

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These are both great points and I’ll make both changes.

Thanks!

- Bret

From: Yao, Jiewen via groups.io<mailto:jiewen.yao=intel.com@groups.io>
Sent: Tuesday, September 15, 2020 7:52 PM
To: Yao, Jiewen<mailto:jiewen.yao@intel.com>; gaoliming<mailto:gaoliming@byosoft.com.cn>; devel@edk2.groups.io<mailto:devel@edk2.groups.io>; Wang, Jian J<mailto:jian.j.wang@intel.com>; bret@corthon.com<mailto:bret@corthon.com>; Bi, Dandan<mailto:dandan.bi@intel.com>
Cc: Wu, Hao A<mailto:hao.a.wu@intel.com>; liming.gao<mailto:liming.gao@intel.com>; Justen, Jordan L<mailto:jordan.l.justen@intel.com>; 'Laszlo Ersek'<mailto:lersek@redhat.com>; 'Ard Biesheuvel'<mailto:ard.biesheuvel@arm.com>; 'Andrew Fish'<mailto:afish@apple.com>; Ni, Ray<mailto:ray.ni@intel.com>
Subject: [EXTERNAL] Re: [edk2-devel] [PATCH v7 11/14] SecurityPkg: Allow VariablePolicy state to delete authenticated variables

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://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla.tianocore.org%2Fshow_bug.cgi%3Fid%3D2522&amp;data=02%7C01%7Cbret.barkelew%40microsoft.com%7C8f1aee9f15a14900a3d508d859eb7222%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637358215630854973&amp;sdata=JyDdXC9JRdBdqfmhAc6fI4R5xhh70wcD0NnNIgwfF3w%3D&amp;reserved=0
>
> 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
>
>
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