# pvimg

`pvimg create` takes a kernel, key files, optionally an initrd image, optionally
a file containing the kernel command line parameters, and generates a single,
bootable image file. The generated image file consists of a concatenation of a
plain text boot loader, the encrypted components for kernel, initrd, kernel
command line, and the integrity-protected Secure Execution header, containing
the metadata necessary for running the guest in protected mode. See [Memory
Layout](#memory-layout) for details about the internal structure of the created
image.

It is possible to use the generated image as a kernel for zipl or for a direct
kernel boot using QEMU.

## Getting started

If all dependencies are met a simple `make` call in the source tree should be
enough for building `pvimg`.

## Details

The main idea of `pvimg create` is:

1. Generate all keys, IVs, and other information needed for the encryption of
   the components and the generation of the PV header
2. add stub stage3a (so we can calculate the memory addresses)
3. add components: prepare the components (alignment and encryption) and add
   them to the memory layout
4. build and add stage3b: generate the stage3b and add it to the memory layout
5. generate the Secure Execution header: generate the hashes (pld, ald, and tld)
   of the components and create the header and IPIB
6. parameterize the stub stage3a: uses the address of the IPIB and Secure
   Execution header
8. write the final image to the specified output path and generate the boot
   image metadata at address `0xc000`. The address `0xc000` is chosen as this is
   the `BSS` section of the stage3a loader and will therefore zeroed out as soon
   as the stage3a is executed and has therefore no leftovers in the memory.

### Boot Loader

The boot loader consists of two parts:

1. stage3a boot loader (cleartext), this loader is responsible for the
   transition into the protected mode by doing `diag308` subcode 8 and 10 calls.
2. stage3b boot loader (encrypted), this loader is very similar to the normal
   zipl stage3 boot loader. It will be loaded by the Ultravisor after the
   successful transition into protected mode. Like the zipl stage3 boot loader
   it moves the kernel and patches in the values for initrd and kernel command
   line.

The loaders have the following constraints:

1. It must be possible to place stage3a and stage3b at a location greater than
   0x10000 because the zipl stage3 loader zeroes out everything at addresses
   lower than 0x10000 of the image.
2. As the stage3 loader of zipl assumes that the passed kernel image looks like
   a normal kernel image, the zipl stage3 loader modifies the content at the
   memory area 0x10400 - 0x10800, therefore we leave this area unused in our
   stage3a loader.
3. The default entry address used by the zipl stage3 loader is 0x10000 so we add
   a simple branch to 0x11000 at 0x10000 so the zipl stage3 loader can modify
   the area 0x10400 - 0x10800 without affecting the stage3a loader.

#### Stage3b

The `stage3b.bin` is linked at address 0x9000, therefore it will not work at
another address. The relocation support for the stage3b loader, so that it can
be loaded at addresses != 0x9000, is added in the loader with the name
`stage3b_reloc.bin`. By default, if we're talking about stage3b we refer to
`stage3b_reloc.bin.`

### Memory Layout

The memory layout of the bootable file looks like:

| Start                    | End        | Use                                                                   |
|--------------------------|------------|-----------------------------------------------------------------------|
| 0                        | 0x7        | Short PSW, starting instruction at 0x11000                            |
| 0x0c000                  | 0x0cfff    | Image metadata, e.g. it includes the file offset of the SE-header     |
| 0x10000                  | 0x10012    | Branch to 0x11000                                                     |
| 0x10013                  | 0x10fff    | Left intentionally unused                                             |
| 0x11000                  | 0x12fff    | Stage3a                                                               |
| 0x14000                  | 0x1[45]fff | SE-header used for the diag308 call (size can be either 1 or 2 pages) |
| `NEXT_PAGE_ALIGNED_ADDR` |            | Encrypted kernel                                                      |
| `NEXT_PAGE_ALIGNED_ADDR` |            | Encrypted kernel parameters                                           |
| `NEXT_PAGE_ALIGNED_ADDR` |            | Encrypted initrd                                                      |
| `NEXT_PAGE_ALIGNED_ADDR` |            | Encrypted stage3b_reloc                                               |
| `NEXT_PAGE_ALIGNED_ADDR` |            | IPIB used as argument for the diag308 call                            |