From ff8b6134756fca6b0c55fedc76aeb5000f783875 Mon Sep 17 00:00:00 2001
From: Laszlo Ersek <lersek@redhat.com>
Date: Fri, 31 Jan 2020 12:42:48 +0100
Subject: [PATCH 12/12] SecurityPkg/DxeImageVerificationHandler: fix "defer"
 vs. "deny" policies
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RH-Author: Laszlo Ersek <lersek@redhat.com>
Message-id: <20200131124248.22369-13-lersek@redhat.com>
Patchwork-id: 93620
O-Subject: [RHEL-8.2.0 edk2 PATCH 12/12] SecurityPkg/DxeImageVerificationHandler: fix "defer" vs. "deny" policies
Bugzilla: 1751993
RH-Acked-by: Philippe Mathieu-Daudé <philmd@redhat.com>
RH-Acked-by: Vitaly Kuznetsov <vkuznets@redhat.com>

In DxeImageVerificationHandler(), we should return EFI_SECURITY_VIOLATION
for a rejected image only if the platform sets
DEFER_EXECUTE_ON_SECURITY_VIOLATION as the policy for the image's source.
Otherwise, EFI_ACCESS_DENIED must be returned.

Right now, EFI_SECURITY_VIOLATION is returned for all rejected images,
which is wrong -- it causes LoadImage() to hold on to rejected images (in
untrusted state), for further platform actions. However, if a platform
already set DENY_EXECUTE_ON_SECURITY_VIOLATION, the platform will not
expect the rejected image to stick around in memory (regardless of its
untrusted state).

Therefore, adhere to the platform policy in the return value of the
DxeImageVerificationHandler() function.

Furthermore, according to "32.4.2 Image Execution Information Table" in
the UEFI v2.8 spec, and considering that edk2 only supports (AuditMode==0)
at the moment:

> When AuditMode==0, if the image's signature is not found in the
> authorized database, or is found in the forbidden database, the image
> will not be started and instead, information about it will be placed in
> this table.

we have to store an EFI_IMAGE_EXECUTION_INFO record in both the "defer"
case and the "deny" case. Thus, the AddImageExeInfo() call is not being
made conditional on (Policy == DEFER_EXECUTE_ON_SECURITY_VIOLATION); the
documentation is updated instead.

Cc: Chao Zhang <chao.b.zhang@intel.com>
Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2129
Fixes: 5db28a6753d307cdfb1cfdeb2f63739a9f959837
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20200116190705.18816-12-lersek@redhat.com>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>
[lersek@redhat.com: push with Mike's R-b due to Chinese New Year
 Holiday: <https://edk2.groups.io/g/devel/message/53429>; msgid
 <d3fbb76dabed4e1987c512c328c82810@intel.com>]
(cherry picked from commit 8b0932c19f31cbf9da26d3b8d4e8d954bdbb5269)

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 .../Library/DxeImageVerificationLib/DxeImageVerificationLib.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c b/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c
index 015a5b6..dbfbfcb 100644
--- a/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c
+++ b/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c
@@ -1548,7 +1548,8 @@ Done:
                                  execution table.
   @retval EFI_ACCESS_DENIED      The file specified by File and FileBuffer did not
                                  authenticate, and the platform policy dictates that the DXE
-                                 Foundation many not use File.
+                                 Foundation may not use File. The image has
+                                 been added to the file execution table.
 
 **/
 EFI_STATUS
@@ -1872,7 +1873,8 @@ DxeImageVerificationHandler (
 
 Failed:
   //
-  // Policy decides to defer or reject the image; add its information in image executable information table.
+  // Policy decides to defer or reject the image; add its information in image
+  // executable information table in either case.
   //
   NameStr = ConvertDevicePathToText (File, FALSE, TRUE);
   AddImageExeInfo (Action, NameStr, File, SignatureList, SignatureListSize);
@@ -1885,7 +1887,10 @@ Failed:
     FreePool (SignatureList);
   }
 
-  return EFI_SECURITY_VIOLATION;
+  if (Policy == DEFER_EXECUTE_ON_SECURITY_VIOLATION) {
+    return EFI_SECURITY_VIOLATION;
+  }
+  return EFI_ACCESS_DENIED;
 }
 
 /**
-- 
1.8.3.1