mirror of
https://github.com/nsacyber/Hardware-and-Firmware-Security-Guidance
synced 2025-08-30 06:07:41 +00:00
Update Windows.md
get-filehash does not provide the appropriate hash for use with secure boot. Get-AppLockerFileInformation does properly process and hash PE files.
This commit is contained in:
43313EB9AA87E7039F8F3948282E61C0CB12372C5499884609A01B2BCA37B973
GitHub
parent
ba934975bd
commit
ed059faed9
@ -1,66 +1,69 @@
|
||||
|
||||
# UEFI Secure Boot Customization for Windows
|
||||
- 1\. Recipes
|
||||
- 1.1. Trust a Driver
|
||||
- 1.2. Distrust a Driver
|
||||
- 1.3. Trust a Boot Component
|
||||
- 1.4. Distrust a Boot Component
|
||||
- 1.5. Edit PK, KEK, DB, or DBX
|
||||
- 1.1. Trust a Boot Component
|
||||
- 1.2. Distrust a Boot Component
|
||||
- 1.3. Edit PK, KEK, DB, or DBX
|
||||
- 2\. Scripts and Commands
|
||||
- 2.1. Create Certificates and Keys
|
||||
- 2.2. Convert from PVK to PFX
|
||||
- 2.3. Sign an EFI Binary or Bootloader
|
||||
- 2.4. Sign a Driver
|
||||
- 2.5. Create Hashes
|
||||
- 2.6. Create EFI Signature List (ESL)
|
||||
- 2.7. Extract Certificates and Hashes from an ESL
|
||||
- 2.8. Backup Secure Boot Values
|
||||
- 2.9. Check a Signature
|
||||
- 2.10. Remove a Signature
|
||||
- 2.4. Create Hashes
|
||||
- 2.5. Create EFI Signature List (ESL)
|
||||
- 2.6. Extract Certificates and Hashes from an ESL
|
||||
- 2.7. Backup Secure Boot Values
|
||||
- 2.8. Check a Signature
|
||||
- 2.9. Remove a Signature
|
||||
- 3\. Examples
|
||||
- 3.1. Trust or Distrust a Driver
|
||||
- 3.2. Modify Hyper-V VM Secure Boot Values
|
||||
- 3.3. Dual Boot a Custom Linux Distribution
|
||||
- 3.4. Mitigate BootHole
|
||||
- 3.1. Modify Hyper-V VM Secure Boot Values
|
||||
- 3.2. Dual Boot a Custom Linux Distribution
|
||||
- 3.3. Mitigate BootHole
|
||||
|
||||
## 1\. Recipes
|
||||
### 1.1. Trust a Driver
|
||||
|
||||
### 1.2. Distrust a Driver
|
||||
Windows drivers are usually signed by one of several trusted sources. Some infrastructure administrators may detect faults, instability, vulnerabilities, user errors, or other issues that necessitate blocking a driver. To block a trusted driver at boot time, create a SHA-256 hash of the driver. Load the hash into Secure Boot's DBX.
|
||||
|
||||
### 1.3. Trust a Boot Component
|
||||
### 1.1. Trust a Boot Component
|
||||
The Windows boot manager includes a signature from Microsoft. The signature is compatible with the standard Secure Boot implementation offered by most vendors. Some users may want to add dual-boot support to allow the use of Linux on the same system as Windows. Other users may want to take advantage of type-1 hypervisor products that must execute at boot time.
|
||||
|
||||
Boot components that change frequently should be signed. The certificate used to validate signatures should be placed in the DB (except when using Linux Shim; then MOK is an option). Boot components that rarely change may be hashed -- SHA-256 -- and the hash placed in the DB.
|
||||
|
||||
### 1.4. Distrust a Boot Component
|
||||
### 1.2. Distrust a Boot Component
|
||||
To distrust a boot component, perform one of the following actions:
|
||||
- Remove the certificate that can validate the component's signature from the DB or MOK.
|
||||
- Remove the SHA-256 hash of the component from the DB or MOK.
|
||||
- Create a SHA-256 hash of the component and add the hash to the DBX or MOKX.
|
||||
|
||||
### 1.5. Edit PK, KEK, DB, or DBX
|
||||
### 1.3. Edit PK, KEK, DB, or DBX
|
||||
If a PK is not present, then Secure Boot must be in Setup Mode to allow initial values to be set. Administrators should place trusted hashes and certificates into the DB, untrusted hashes and certificates into the DBX, and place certificates for trustworthy update signers in the KEK. The PK certificate should be set last -- setting the PK locks out unsigned changes to the KEK, DB, and DBX.
|
||||
|
||||
Systems that already have a PK may perform runtime updates. Any changes to the KEK must be signed by the PK. Any changes to the DB or DBX must be signed by a KEK.
|
||||
|
||||
## 2\. Scripts and Commands
|
||||
### 2.1. Create Certificates and Keys
|
||||
The built-in makecert command can be used instead of OpenSSL. Use the following commands to create a KEK certificate and a DB certificate. CER denotes DER-encoded certificates. Keys are stored as PVK private keys.
|
||||
```
|
||||
makecert -n "CN=Custom KEK" -a sha256 -r -sv KEK.pvk KEK.cer
|
||||
makecert -n "CN=Custom DBK" -a sha256 -r -sv DBK.pvk DBK.cer
|
||||
```
|
||||
|
||||
### 2.2. Convert from PVK to PFX
|
||||
Some tools require a PKCS#12 key format. The Windows PVK format may not be accepted. Convert the PVK files to PFX using the following commands.
|
||||
```
|
||||
pvk2pfx -pvk KEK.pvk -spc KEK.cer -pfx KEK.pfx -f
|
||||
pvk2pfx -pvk DBK.pvk -spc DBK.cer -pfx DBK.pfx -f
|
||||
```
|
||||
|
||||
### 2.3. Sign an EFI Binary or Bootloader
|
||||
The following command signs the pre-bootloader, Shim. Instructing a Windows system to boot to Shim involves utilizing BCDEdit (see section 3).
|
||||
```
|
||||
signtool sign /f DBK.pfx /fd sha256 shimx64.efi
|
||||
```
|
||||
|
||||
### 2.4. Sign a Driver
|
||||
### 2.4. Create Hashes
|
||||
The alternative to signing bootable content is to create a hash. Hashes must be in the SHA-256 format. EFI binaries are considered PE (Portable Executable) files that contain a DOS/WINNT header, obey a structural schema, and omit some information from the contents that should be hashed. Use PowerShell Get-AppLockerFileInformation to compute the correct hashes.
|
||||
|
||||
### 2.5. Create Hashes
|
||||
Earlier versions of this repository and the UEFI Secure Boot Customization technical report erroneously advise the use of sha256sum, get-filehash, and other whole-file hashing mechanisms. Only use solutions that are aware of the PE COFF file format and Microsoft Authenticode signing paradigms.
|
||||
```
|
||||
get-filehash -algorithm SHA256 shimx64.efi | select -ExpandProperty hash > shimx64.txt
|
||||
$hashString = get-filehash -algorithm SHA256 shimx64.efi | select -ExpandProperty hash
|
||||
$hashString = Get-AppLockerFileInformation shimx64.efi | select -ExpandProperty hash | select -ExpandProperty HashDataString
|
||||
$hashString.Trim("0x") > shimx64.txt
|
||||
$hashBytes = [byte[]]::new($hashString.length / 2)
|
||||
For($i=0; $i -lt $hashString.length; $i+=2) {
|
||||
$hashBytes[$i/2] = [convert]::ToByte($hashString,Substring($i, 2), 16)
|
||||
@ -68,11 +71,11 @@ For($i=0; $i -lt $hashString.length; $i+=2) {
|
||||
$hashBytes | set-content shimx64.hsh -encoding byte
|
||||
```
|
||||
|
||||
### 2.6. Create EFI Signature List (ESL)
|
||||
### 2.5. Create EFI Signature List (ESL)
|
||||
|
||||
### 2.7. Extract Certificates and Hashes from an ESL
|
||||
### 2.6. Extract Certificates and Hashes from an ESL
|
||||
|
||||
### 2.8. Backup Secure Boot Values
|
||||
### 2.7. Backup Secure Boot Values
|
||||
```
|
||||
Get-SecureBootUEFI -Name PK -OutputFilePath PK.esl
|
||||
Get-SecureBootUEFI -Name KEK -OutputFilePath KEK.esl
|
||||
@ -80,21 +83,19 @@ Get-SecureBootUEFI -Name DB -OutputFilePath DB.esl
|
||||
Get-SecureBootUEFI -Name DBX -OutputFilePath DBX.esl
|
||||
```
|
||||
|
||||
### 2.9. Check a Signature
|
||||
### 2.8. Check a Signature
|
||||
```
|
||||
Get-AuthenticodeSignature -FilePath shimx64.efi
|
||||
```
|
||||
|
||||
### 2.10. Remove a Signature
|
||||
### 2.9. Remove a Signature
|
||||
```
|
||||
signtool remove /s shimx64.efi
|
||||
```
|
||||
|
||||
## 3\. Examples
|
||||
### 3.1. Trust or Distrust a Driver
|
||||
### 3.1. Modify Hyper-V VM Secure Boot Values
|
||||
|
||||
### 3.2. Modify Hyper-V VM Secure Boot Values
|
||||
### 3.2. Dual Boot a Custom Linux Distribution
|
||||
|
||||
### 3.3. Dual Boot a Custom Linux Distribution
|
||||
|
||||
### 3.4. Mitigate BootHole
|
||||
### 3.3. Mitigate BootHole
|
||||
|
||||
Loading…
x
Reference in New Issue
Block a user