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UEFI 2.x section 3.1.2 provides for "short-form device path", where the first element specified is a "hard drive media device path", so that you can move a disk around on different buses without invalidating your device path. Fallback has not been using this option, though in most cases efibootmgr has. Note that we still keep the full device path, because LoadImage() isn't necessarily the layer where HD() works - one some systems BDS is responsible for resolving the full path and passes that to LoadImage() instead. So we have to do LoadImage() with the full path. |
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|---|---|---|
| Cryptlib | ||
| include | ||
| lib | ||
| .gitignore | ||
| cert.S | ||
| COPYRIGHT | ||
| crypt_blowfish.c | ||
| crypt_blowfish.h | ||
| elf_ia32_efi.lds | ||
| elf_ia64_efi.lds | ||
| elf_x86_64_efi.lds | ||
| fallback.c | ||
| make-certs | ||
| Makefile | ||
| MokManager.c | ||
| MokVars.txt | ||
| netboot.c | ||
| netboot.h | ||
| PasswordCrypt.c | ||
| PasswordCrypt.h | ||
| README | ||
| replacements.c | ||
| replacements.h | ||
| shim.c | ||
| shim.h | ||
| TODO | ||
| ucs2.h | ||
| version.c.in | ||
| version.h | ||
shim is a trivial EFI application that, when run, attempts to open and execute another application. It will initially attempt to do this via the standard EFI LoadImage() and StartImage() calls. If these fail (because secure boot is enabled and the binary is not signed with an appropriate key, for instance) it will then validate the binary against a built-in certificate. If this succeeds and if the binary or signing key are not blacklisted then shim will relocate and execute the binary. shim will also install a protocol which permits the second-stage bootloader to perform similar binary validation. This protocol has a GUID as described in the shim.h header file and provides a single entry point. On 64-bit systems this entry point expects to be called with SysV ABI rather than MSABI, and so calls to it should not be wrapped. To use shim, simply place a hex dump of the public certificate in cert.h and build it with make.