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1 | # shim, a first-stage UEFI bootloader | |
2 | ||
3 | shim is a trivial EFI application that, when run, attempts to open and | |
4 | execute another application. It will initially attempt to do this via the | |
5 | standard EFI `LoadImage()` and `StartImage()` calls. If these fail (because Secure | |
6 | Boot is enabled and the binary is not signed with an appropriate key, for | |
7 | instance) it will then validate the binary against a built-in certificate. If | |
8 | this succeeds and if the binary or signing key are not forbidden then shim | |
9 | will relocate and execute the binary. | |
10 | ||
11 | shim will also install a protocol which permits the second-stage bootloader | |
12 | to perform similar binary validation. This protocol has a GUID as described | |
13 | in the shim.h header file and provides a single entry point. On 64-bit systems | |
14 | this entry point expects to be called with SysV ABI rather than MSABI, so calls | |
15 | to it should not be wrapped. | |
16 | ||
17 | On systems with a TPM chip enabled and supported by the system firmware, | |
18 | shim will extend various PCRs with the digests of the targets it is | |
19 | loading. A full list is in the file [README.tpm](README.tpm) . | |
20 | ||
21 | To use shim, simply place a DER-encoded public certificate in a file such as | |
22 | pub.cer and build with `make VENDOR_CERT_FILE=pub.cer`. | |
23 | ||
24 | There are a couple of build options, and a couple of ways to customize the | |
25 | build, described in [BUILDING](BUILDING). | |
26 | ||
27 | See the [test plan](testplan.txt), and file a ticket if anything fails! |