KernelModule file is a file that can be loaded into the kernel at runtime, it's a binary file that contains the code and data that can be loaded into the kernel and run. And for the security concern we need to sign and verify the KernelModule file to make sure the file was not tampered.
There are two files located in the kernel repository that can be used to sign and verify the KernelModule file, they are scripts/sign-file.c and scripts/extract-module-sig.pl.
The sign-file.c is used to sign the KernelModule file and the scripts/extract-module-sig.pl is used to extract the certificate from the signed KernelModule file.
The layout of signed KernelModule file is describe as below:
- The raw content of kernel module file.
- The CMS signature, and signature is a DER encoded PKCS#7 structure. The PKCS#7 structure contains the certificate and the signature of the file.
- The ModuleSignature structure is appended after in the PKCS#7 structure, which contains the information of the signature.
- The Module Magic string ("
Module signature appended\n"), and it will be appended after the ModuleSignature structure, which is used to identify the signature.
For Ubuntu, you can locate the sign-file tool with command:
tommylike@ubuntu ~ /usr/src/linux-headers-$(uname -r)/scripts/sign-file
Usage: scripts/sign-file [-dp] <hash algo> <key> <x509> <module> [<dest>]
scripts/sign-file -s <raw sig> <hash algo> <x509> <module> [<dest>]sign-file support detached(-pd) and attached(-p) signature, considering you have generated the x509 key and cert, the command would as simple as:
tommylike@ubuntu ~ /usr/src/linux-headers-$(uname -r)/scripts/sign-file -dp sha256 new.key new.crt simple.koCommand used to check the cms signature in text format:
tommylike@ubuntu ~/sign-kernelmodule openssl pkcs7 -in simple.ko.p7s -inform DER -text
-----BEGIN PKCS7-----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-----END PKCS7-----or in ASN.1 format:
tommylike@ubuntu ~/sign-kernelmodule openssl asn1parse -inform der -in simple.ko.p7s
0:d=0 hl=4 l= 458 cons: SEQUENCE
4:d=1 hl=2 l= 9 prim: OBJECT :pkcs7-signedData
15:d=1 hl=4 l= 443 cons: cont [ 0 ]
19:d=2 hl=4 l= 439 cons: SEQUENCE
23:d=3 hl=2 l= 1 prim: INTEGER :01
26:d=3 hl=2 l= 13 cons: SET
28:d=4 hl=2 l= 11 cons: SEQUENCE
30:d=5 hl=2 l= 9 prim: OBJECT :sha256
41:d=3 hl=2 l= 11 cons: SEQUENCE
43:d=4 hl=2 l= 9 prim: OBJECT :pkcs7-data
54:d=3 hl=4 l= 404 cons: SET
58:d=4 hl=4 l= 400 cons: SEQUENCE
62:d=5 hl=2 l= 1 prim: INTEGER :01
65:d=5 hl=2 l= 107 cons: SEQUENCE
67:d=6 hl=2 l= 102 cons: SEQUENCE
69:d=7 hl=2 l= 14 cons: SET
71:d=8 hl=2 l= 12 cons: SEQUENCE
73:d=9 hl=2 l= 3 prim: OBJECT :commonName
78:d=9 hl=2 l= 5 prim: UTF8STRING :infra
85:d=7 hl=2 l= 14 cons: SET
87:d=8 hl=2 l= 12 cons: SEQUENCE
89:d=9 hl=2 l= 3 prim: OBJECT :organizationalUnitName
94:d=9 hl=2 l= 5 prim: UTF8STRING :Infra
101:d=7 hl=2 l= 15 cons: SET
103:d=8 hl=2 l= 13 cons: SEQUENCE
105:d=9 hl=2 l= 3 prim: OBJECT :organizationName
110:d=9 hl=2 l= 6 prim: UTF8STRING :Huawei
118:d=7 hl=2 l= 17 cons: SET
120:d=8 hl=2 l= 15 cons: SEQUENCE
122:d=9 hl=2 l= 3 prim: OBJECT :localityName
127:d=9 hl=2 l= 8 prim: UTF8STRING :ShenZhen
137:d=7 hl=2 l= 19 cons: SET
139:d=8 hl=2 l= 17 cons: SEQUENCE
141:d=9 hl=2 l= 3 prim: OBJECT :stateOrProvinceName
146:d=9 hl=2 l= 10 prim: UTF8STRING :Guang Dong
158:d=7 hl=2 l= 11 cons: SET
160:d=8 hl=2 l= 9 cons: SEQUENCE
162:d=9 hl=2 l= 3 prim: OBJECT :countryName
167:d=9 hl=2 l= 2 prim: PRINTABLESTRING :CN
171:d=6 hl=2 l= 1 prim: INTEGER :00
174:d=5 hl=2 l= 11 cons: SEQUENCE
176:d=6 hl=2 l= 9 prim: OBJECT :sha256
187:d=5 hl=2 l= 13 cons: SEQUENCE
189:d=6 hl=2 l= 9 prim: OBJECT :rsaEncryption
200:d=6 hl=2 l= 0 prim: NULL
202:d=5 hl=4 l= 256 prim: OCTET STRING [HEX DUMP]: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 support sign KernelModule file within the command as following:
RUST_BACKTRACE=full RUST_LOG=debug ./target/debug/client --config /path/to/client.toml add --key-name default-x509 --file-type kernel-module --key-type x509 .data/simple.koSignatrust supports to resign a signed KernelModule file, that's to say instead of append the cert and metadata at the end of file, signatrust will try to parse the kernel module file and replace the signature when resigning.
if you add the --detached flag, the signature will be detached from the file as sign-file tool, and the signature will be output to the file with the same name as the file to be signed, but with the extension .p7s appended to the file name.
RUST_BACKTRACE=full RUST_LOG=debug ./target/debug/client --config /path/to/client.toml add --key-name default-x509 --file-type kernel-module --key-type x509 --detached .data/simple.koIn order to verify the signature of KernelModule file, you need to extract the signature from the file first, and then verify the signature with the extracted signature and the original file.
- Download the certificate from signatrust control-server and save it into local file(new.cert as below) in pem format:
curl -X 'POST' \
'https://localhost:8080/api/v1/keys/<key-id-or-name>/certificate' \
-H 'accept: application/json' \
-H 'Authorization: cBnLPLXl1fA7fKDZnjg9fd9dSWw2RXtUH3MGFUtq' \
-d ''- Extract the signature from the KernelModule file or use detached signature(.p7s)
tommylike@ubuntu ~/sign-kernelmodule perl extract-module-sig.pl -s simple.ko > detached.p7s
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
LANGUAGE = (unset),
LC_ALL = (unset),
LC_TERMINAL = "iTerm2",
LC_CTYPE = "UTF-8",
LANG = "en_US.UTF-8"
are supported and installed on your system.
perl: warning: Falling back to a fallback locale ("en_US.UTF-8").
Read 15805 bytes from module file
Found magic number at 15805
Found PKCS#7/CMS encapsulation
Found 461 bytes of signature [308201c906092a864886f70d010702a0]- Verify the signature
openssl smime -verify -binary -inform DER -in detached.p7s -content simple.ko -certfile new.crt -nointern -noverify
......
......
Verification successful- Display signature In order to view the detail of signature, we can convert signature into cms format and view detail with openssl cms sub command.
openssl cms -verify -noverify -in detached.p7s -inform DER -cmsout -out detached.cms
openssl cms -cmsout -print -noout -in detached.cms
CMS_ContentInfo:
contentType: pkcs7-signedData (1.2.840.113549.1.7.2)
d.signedData:
version: 1
digestAlgorithms:
algorithm: sha256 (2.16.840.1.101.3.4.2.1)
parameter: <ABSENT>
encapContentInfo:
eContentType: pkcs7-data (1.2.840.113549.1.7.1)
eContent: <ABSENT>
certificates:
<EMPTY>
crls:
<EMPTY>
signerInfos:
version: 1
d.issuerAndSerialNumber:
issuer: CN=Infra, OU=Infra, O=Huawei, L=ShenZhen, ST=GuangDong, C=CN
serialNumber: 0xB2A68D95D9B92D92E48FDB184FA0BC8B
digestAlgorithm:
algorithm: sha256 (2.16.840.1.101.3.4.2.1)
parameter: <ABSENT>
signedAttrs:
object: contentType (1.2.840.113549.1.9.3)
value.set:
OBJECT:pkcs7-data (1.2.840.113549.1.7.1)
object: signingTime (1.2.840.113549.1.9.5)
value.set:
UTCTIME:Jul 21 08:49:06 2023 GMT
object: messageDigest (1.2.840.113549.1.9.4)
value.set:
OCTET STRING:
0000 - ff 87 d2 69 59 94 92 d3-28 a9 53 39 81 ...iY...(.S9.
000d - 8e b3 95 ff 97 82 59 e4-f2 19 07 52 bc ......Y....R.
001a - 32 ad 97 df cd e6 2.....
signatureAlgorithm:
algorithm: rsaEncryption (1.2.840.113549.1.1.1)
parameter: NULL
signature:
0000 - 1d b0 07 d7 23 cd 0e 39-47 7f 64 2a b0 57 7c ....#..9G.d*.W|
000f - b8 8a 38 33 4b 36 ea 7a-23 9a ba ac 5a 9f c1 ..83K6.z#...Z..
001e - 48 4e ca 65 86 3e c2 27-1f 2e bd 02 7b 75 8c HN.e.>.'....{u.
002d - fd d1 d0 06 32 65 58 10-bf 8f c4 4c a2 6a 77 ....2eX....L.jw
003c - 9f 36 df c6 ab 90 02 de-54 b1 96 a9 50 0a b7 .6......T...P..
004b - f7 2e 5d 72 b1 07 0a 78-ae a3 c3 06 1e a0 9c ..]r...x.......
005a - c3 e8 7e 10 5f 97 39 5b-fe 86 9b 58 cf f5 d2 ..~._.9[...X...
0069 - 3c 61 a0 ca cc 12 48 3c-d4 86 1c 1b fb 3a 47 <a....H<.....:G
0078 - 2f 31 01 45 a2 ce 32 cc-09 9b 24 18 95 3c ed /1.E..2...$..<.
0087 - d1 bf c6 b4 9c 4f 73 dd-10 ab c0 d7 42 ba 13 .....Os.....B..
0096 - 51 d0 e7 6f 60 84 80 56-ba 33 3f 09 ef 2a 6d Q..o`..V.3?..*m
00a5 - c7 84 1c 9e 64 07 bf 9d-ea 1c 9c 59 14 39 77 ....d......Y.9w
00b4 - 12 92 d4 8d cf 0c 6f c4-bd 9a ca 3e ec 54 1a ......o....>.T.
00c3 - ed 5a 87 8c 47 33 53 58-b8 5b 98 ff bb aa 1b .Z..G3SX.[.....
00d2 - cf f3 23 cb a4 48 93 4b-87 fe 7d ba da 96 6d ..#..H.K..}...m
00e1 - 56 57 6e 7d 25 4c e7 6e-39 27 c3 f3 06 58 72 VWn}%L.n9'...Xr
00f0 - 2f d8 27 cc ce 78 22 18-df 8a c2 91 29 87 a2 /.'..x".....)..
00ff - 62 b
unsignedAttrs:
<EMPTY>