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View Code? Open in Web Editor NEWSecure EFI Loader designed to authenticate the non-PE files
License: BSD 3-Clause "New" or "Revised" License
Secure EFI Loader designed to authenticate the non-PE files
License: BSD 3-Clause "New" or "Revised" License
Secure EFI Loader ================= The SELoader is designed to authenticate the non-PE files, such as grub configuration, initrd, grub modules, which cannot be verified by the MOK Verify Protocol registered by shim loader. In order to conveniently authenticate the PE file with gBS->LoadImage() and gBS->StartImage(), the SELoader hooks EFI Security2 Architectural Protocol and employs MOK Verify Protocol to verify the PE file. If only UEFI Secure Boot is enabled, the SELoader just simplily calls gBS->LoadImage() and gBS->StartImage() to allow BIOS to verify PE file. The SELoader publishes MOK2 Verify Protocol which provides a flexible interface to allow the bootloader to verify the file, file buffer or memory buffer without knowing the file format. In order to establish the chain of trust, the SELoader is required to be signed by a private key corresponding to a DB certificate, the shim certificate, the vendor certificate or a shim MOK certificate. The specific key is determined by the Secure Boot scheme you will use. Using UEFI Secure Boot, MOK Verify Protocol and the SELoader together, the boot process is completely trustworthy. ESP Layout ---------- A typical ESP layout for x86-64 looks like below, e.g, . ├── EFI │ └── BOOT │ ├── bootx64.efi │ ├── grub.cfg │ ├── grub.cfg.p7b │ ├── grubx64.efi │ ├── Hash2DxeCrypto.efi │ ├── LockDown.efi │ ├── mmx64.efi │ ├── Pkcs7VerifyDxe.efi │ ├── SELoaderx64.efi │ └── x86_64-efi │ ├── ... │ ├── mok2verify.mod │ └── ... ├── images │ ├── bzImage │ ├── bzImage.p7b │ ├── initrd │ └── initrd.p7b └── startup.nsh where: - bootx64.efi The first stage shim loader, signed by DB key and authenticated by UEFI BIOS boot manager. - SELoaderx64.efi The second stage loader, authenticated by the shim loader with the vendor certificate, shim certificate, MOK certificate or DB certificate. - grubx64.efi The third stage loader, authenticated by the SELoader with the same objects as mentioned in SELoaderx64.efi. - grub.cfg grub configuration file. - grub.cfg.p7b The signature file of grub.cfg, authenticated by the SELoader. - mok2verify.mod Providing MOK2 Verify Protocol support, allowing the grub loader to call SELoader to verify grub.cfg.p7b, bzImage.p7b and initrd.p7b. - bzImage Linux kernel. - bzImage.p7b The signature file of bzImage, authenticated by the SELoader. - initrd initramfs image. - initrd.p7b The signature file of initrd, authenticated by the SELoader. - LockDown.efi Run the automatical certificate provision for UEFI Secure Boot. - mmx64.efi MOK Secure Boot manager, authenticated by the shim loader. - Pkcs7VerifyDxe.efi Providing EFI Pkcs7 Verify Protocol support, authenticated by the SELoader. - Hash2DxeCrypto.efi Providing EFI Hash2 Protocol support, authenticated by the SELoader. - startup.nsh UEFI shell bootstrap script. All efi binaries are signed with either DB.key or vendor_cert.key per the secure boot scheme you choose. Refer to meta-secure-env for practical secure boot implementation, and the signing tool sbsigntool. Note that the SELoader can be also used alone without the shim loader. EFI Pkcs7 Verify Protocol ------------------------- The SELoader employs EFI PKCS7 Verify Protocol available since UEFI Specification version 2.5 to verify the signature to prove the integrity of checked file. If your BIOS doesn't support this protocol, it is recommended to update the BIOS to the latest. If the latest still doesn't support the protocol, the SELoader is able to load the Pkcs7VerifyDxe.efi driver if available. Usually, the Pkcs7VerifyDxe.efi driver is located in the directory where the SELoader resides on ESP. You can build the Pkcs7VerifyDxe.efi driver from the scratch if you would like to do it. Refer to Bin/README for the instructions. Known Issues ------------ - The PKCS#7 detached signature format (.p7s) is not supported. References ---------- libsign - the signing tool used to generate SELoader PKCS#7 signature https://github.com/jiazhang0/libsign grub - Mok2Verify patch to verify the grub.cfg, linux kernel and initrd https://github.com/jiazhang0/meta-secure-core/blob/master/meta-efi-secure-boot/recipes-bsp/grub/grub-efi/mok2verify-support-to-verify-non-PE-file-with-PKCS-7.patch shim - implement MOK verify protocol https://github.com/rhboot/shim meta-secure-core - a practical secure boot implementation based on oe-core https://github.com/jiazhang0/meta-secure-core SecureCore - a complete OpenEmbedded/Poky-compatible reference implementation based on meta-secure-core https://github.com/jiazhang0/SecureCore
While linking SELoader I get the following error:
Efi/Lib/libSELoader.a(Image.o): In function LoadImage':Image.c:(.text+0x26): undefined reference to
gEfiLoadedImageProtocolGuid'
x86_64-poky-linux-ld:Efi/Lib/libSELoader.a(Image.o): relocation R_X86_64_PC32 against undefined hidden symbol `gEfiLoadedImageProtocolGuid' can not be used when making a shared object
x86_64-poky-linux-ld: final link failed: Bad value
I can see why this happens:
In Src/Efi/Lib/Image.c EfiLoadedImageProtocolGuid declaration is dependent on:
#if GNU_EFI_VERSION <= 303
Then in LoadImage(), EfiLoadedImageProtocolGuid is accessed unconditionally:
Status = EfiProtocolOpen(gThisImage, &gEfiLoadedImageProtocolGuid,
(VOID **)&LoadedImage);
Causing the undefined symbol.
Therefore if the GNU_EFI_VERSION is > 303, linking will fail.
Is this the correct behaviour? Should versions of gnu-efi above 3.0.3 be supported with some alternative? Or is it intended, that only versions below 3.0.3 are supported (despite Mak.env having a default of 3.0.5)?
Hi Jia,
I'm running into a problem, with upstream SecureCore on qemu, grubx64.efi and grub.cfg.p7b checking are bypassed. For example, if grub.cfg.p7b is removed or grubx64.efi is signed by a unknown key, seloader can boot grub, which is not an expected behavior.
Sounds in MokVerifyProtocolInstalled(), seloader can't locate gEfiMokVerifyProtocolGuid, see:
Status = EfiProtocolLocate(&gEfiMokVerifyProtocolGuid,
(VOID **)&MokVerifyProtocol);
I guess gEfiMokVerifyProtocolGuid is installed by shim loader, but why this protocol is not located by seloader?
Can you help with this?
Thanks,
Yunguo
Does this support opening files in locations other than where the module itself resides? For example, if I have (hd0,gpt1) as where SELoader (and shim and everything else reside) and wish to have GRUB load from a FAT partition that's on (hd0,gpt2) instead AFAICT SELoader (and Mok2Verify) is passing back FILE_NOT_FOUND even if yes, the file really does exist. Any pointers greatly appreciated, thanks!
It doesn't seem to verify grub modules even though README claims it. Am I missing something?
I'm also thinking about fonts. How do you handle them?
I tried to workaround the issue with grub-mkstandalone but it didn't work with secure booting. Probably the problem is that SELoader doesn't support separated filesystems. Right?
Is it enough to embed all needed modules with grub-mkimage?
The SELoader built failed with gnu-efi 3.0.8:
| /build/tmp-glibc/work/core2-64-wrs-linux/seloader/0.4.5+gitAUTOINC+9c2723afae-r0/recipe-sysroot/usr/lib64/libefi.a(str.o): In function StrnCpy': | /usr/src/debug/gnu-efi/3.0.8-r0/gnu-efi-3.0.8//lib/str.c:124: multiple definition of
StrnCpy'
| /build/tmp-glibc/work/core2-64-wrs-linux/seloader/0.4.5+gitAUTOINC+9c2723afae-r0/git/Src/Efi/Lib/BaseLibrary/libBaseLibrary.a(StrnCpy.o):StrnCpy.c:(.text+0x0): first defined here
| /build/tmp-glibc/work/core2-64-wrs-linux/seloader/0.4.5+gitAUTOINC+9c2723afae-r0/git/Rules.mk:9: recipe for target 'SELoader.so' failed
| make[2]: *** [SELoader.so] Error 1
This is because gnu-efi 3.0.8 also define StrnCpy function in the following commit:
commit 9485c65f6d28b71ff697849c1c8d47fd077ccd07
Author: Peter Jones [email protected]
Date: Tue Mar 13 15:20:28 2018 -0400
gnu-efi: add some more common string functions.
This adds bounded string helper functions:
StrnLen()
StrnCpy()
StrnCat()
StpnCpy()
And the unbounded function StpCpy().
Signed-off-by: Peter Jones <[email protected]>
Signed-off-by: Nigel Croxon <[email protected]>
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