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SecurityPkg/DxeImageVerificationHandler: fix "defer" vs. "deny" policies 

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: 5db28a6753
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>]
This commit is contained in:
Laszlo Ersek 2020-01-16 14:45:38 +01:00 committed by mergify[bot]
parent 6aa31db5eb
commit 8b0932c19f
1 changed files with 8 additions and 3 deletions
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11
SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c
View File

@ -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;
}
/**