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[PATCH] SecurityPkg: check return value of GetEfiGlobalVariable2() in DxeImageVerificationHandler()
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Jon Maloy
Fixes: CVE-2019-14560
GetEfiGlobalVariable2() is used in some instances when looking up the SecureBoot UEFI variable. The API can fail in certain circumstances, for example, if AllocatePool() fails or if gRT->GetVariable() fails. In the case of secure boot checks, it is critical that this return value is checked. if an attacker can cause the API to fail, it would currently constitute a secure boot bypass. This return value check is missing in the function DxeImageVerificationHandler(), so we add it here. This commit is almost identical to one suggested by Jian J Wang <jian.j.wang@...> on 2019-09-09, but that one was for some reason never posted to the edk2-devel list. We now make a new attempt to get it reviewed and applied. Cc: Jiewen Yao <jiewen.yao@...> Cc: Jian J Wang <jian.j.wang@...> Cc: Min Xu <min.m.xu@...> Cc: devel@edk2.groups.io Signed-off-by: Jon Maloy <jmaloy@...> --- .../DxeImageVerificationLib.c | 39 +++++++++++-------- 1 file changed, 23 insertions(+), 16 deletions(-) diff --git a/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c b/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c index 66e2f5eaa3c0..4ae0bd8b20db 100644 --- a/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c +++ b/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c @@ -1686,6 +1686,7 @@ DxeImageVerificationHandler ( RETURN_STATUS PeCoffStatus; EFI_STATUS HashStatus; EFI_STATUS DbStatus; + EFI_STATUS SecBootStatus; BOOLEAN IsFound; SignatureList = NULL; @@ -1742,23 +1743,29 @@ DxeImageVerificationHandler ( CpuDeadLoop (); } - GetEfiGlobalVariable2 (EFI_SECURE_BOOT_MODE_NAME, (VOID **)&SecureBoot, NULL); - // - // Skip verification if SecureBoot variable doesn't exist. - // - if (SecureBoot == NULL) { - return EFI_SUCCESS; - } + SecBootStatus = GetEfiGlobalVariable2 (EFI_SECURE_BOOT_MODE_NAME, (VOID **)&SecureBoot, NULL); + if (!EFI_ERROR (SecBootStatus)) { + if (SecureBoot == NULL) { + // + // Skip verification if SecureBoot variable doesn't exist. + // + return EFI_SUCCESS; + } else { + // + // Skip verification if SecureBoot is disabled but not AuditMode + // + if (*SecureBoot == SECURE_BOOT_MODE_DISABLE) { + FreePool (SecureBoot); + return EFI_SUCCESS; + } + FreePool (SecureBoot); + } + } else { + // + // Assume SecureBoot enabled in the case of error. + // + } - // - // Skip verification if SecureBoot is disabled but not AuditMode - // - if (*SecureBoot == SECURE_BOOT_MODE_DISABLE) { - FreePool (SecureBoot); - return EFI_SUCCESS; - } - - FreePool (SecureBoot); // // Read the Dos header. -- 2.35.3 |
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Yao, Jiewen
Thanks for the patch.
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Would you please share the info that, how this patch is tested? Have you created a situation to cause GetEfiGlobalVariable2() returns failure here? -----Original Message----- |
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